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Eocladoxylon ( Protopteridium ) minutum (Halle) Koidzumi from the Middle Devonian of Yunnan, China: An Early Rhacophyton ‐Like Plant?
Abstract
New specimens of Eocladoxylon (Protopteridium) minutum (Halle) Koidzumi collected from the Middle Devonian Xichong Formation, Yunnan province, China, demonstrate three orders of branching. Sterile branching systems have a pinnate two-dimensional branching pattern with alternate insertion of lower orders. Up to several times deeply dissected, overall wedge-shaped, flattened appendages are inserted alternately on the third order of branching. Second and third orders of branching have an opposite pair of similar appendages inserted at the base, perpendicular to the plane of the remaining branching system. Fertile appendages, consisting of a dichotomous axial system and terminal pairs of sporangia attached closely in groups of eight, replace the sterile appendages in fertile branches. Anatomy of a probable second-order axis demonstrates a bipolar clepsydroid vascular system. The sterile branching system and anatomy bear some similarity to the Late Devonian fernlike plant Rhacophyton. Eocladoxylon is neither a cladoxylopsid nor a progymnosperm, as was previously believed. The potential for an ancestor/descendant relationship between Iridopteridales and Rhacophyton via Eocladoxylon is briefly discussed in the context of the geographical isolation of the Middle Devonian flora of South China.
... Moniliform "ferns" consist primarily of assemblages of compressed and/or anatomically preserved plant fragments that occur in deposits ranging from the Middle Devonian to the Permian ( Fig. 4.2.2). Representatives with the simplest structure have features that intergrade with trimerophyte-grade euphyllophytes (e.g., Hilton, 1999), whereas, those with somewhat more complex structure intergrade with each other and with plants that represent lignophytes and equisetophytes (e.g., Berry & Wang, 2006). As a result, moniliform fossils sometimes are allied with modern ferns and at other times are regarded as ancestral (or sister groups) to equisetophytes (Stein 1982), but hypothesized sister group relationships with modern euphyllophytes have not been confirmed for any of the Devonian moniliforms. ...
... To complicate identification and classification of moniliform plants further, a large percentage of species are known only from small segments of the branching systems. Some generic and specific concepts are based on compression/impression fossils that show primarily gross morphology, while others are derived from segments of permineralized axes that show primarily internal anatomy and branching pattern for only one or two branching orders (e.g., Stein & Hueber 1989;Berry & Wang, 2006). Only a few are known from a variety of modes of preservation that represent all of the organs of the sporophyte. ...
... In our current treatment, moniliforms are organized as cladoxylopsids/iridopterids, stauropterids, and zygopterids ( Fig. 4.2.1), but many of the most ancient moniliform fossils are hard to classify with precision (see Berry & Wang, 2006, for an illustration of the difficulties). ...
Introduction Ferns traditionally have been identified as megaphyllous plants that reproduce by sporangia borne on leaves (i.e., fronds; Bower 1923; Kaplan and Groff, 1995). Although not all species have the entire set of characters, ferns typically are recognized by sporophytes that display unipolar growth (Rothwell, 1995), are dominated by fronds (Kaplan and Groff, 1995), and are devoid of secondary growth. Many have highly branched fronds, mesarch xylem maturation, and a rhizome stele that is dissected by leaf gaps. Plants that display various combinations of these features occur in the fossil record from the Middle Devonian (i.e., 390 million years ago) to the Recent, but there has been considerable systematic turnover with several prominent clades replacing one another through geological time (Rothwell, 1999). In practice, botanists have traditionally recognized as “ferns” those species that are left over after all other euphyllophytes have been removed to clades with clearly identifiable synapomorphies (Rothwell, 1999). Up to the present, attempts to define ferns within a phylogenetic framework have met with only limited success (Figure 13.1) due to a combination of (1) limited information about many extinct ferns and fern-like plants, and (2) the restricted taxon sampling available for phylogenetic analyses that include only living species. The paleontological record of ferns is incomplete, and thus far has been sampled for only a small fraction of the available fossils (Stockey and Rothwell, 2006). This leaves us with an often confusing picture of inadequately known extinct species that can be difficult to comprehend and appreciate. © Cambridge University Press 2008 and Cambridge University Press 2009.
... Rhacophytales (sensu Taylor et al., 2009) consists of Chlidanophyton (Gensel, 1973), Ellesmeris (Hill et al., 1997), Eocladoxylon (Berry and Wang, 2006), Protocephalopteris (Schweitzer, 1968), Protopteridophyton (Li and Hsü, 1987) and Rhacophyton (Andrews and Phillips, 1968). Chlidanophyton, Eocladoxylon and Protopteridophyton are of unknown affinity at the ordinal level because they combine the morphological and/or anatomical features of multiple plant groups (Gensel, 1973;Li and Hsü, 1987;Berry and Wang, 2006). ...
... Rhacophytales (sensu Taylor et al., 2009) consists of Chlidanophyton (Gensel, 1973), Ellesmeris (Hill et al., 1997), Eocladoxylon (Berry and Wang, 2006), Protocephalopteris (Schweitzer, 1968), Protopteridophyton (Li and Hsü, 1987) and Rhacophyton (Andrews and Phillips, 1968). Chlidanophyton, Eocladoxylon and Protopteridophyton are of unknown affinity at the ordinal level because they combine the morphological and/or anatomical features of multiple plant groups (Gensel, 1973;Li and Hsü, 1987;Berry and Wang, 2006). Here we consider these three genera as fern-like plants with terminal sporangia on branches. ...
... The stem of Shougangia may be prostrate where adventitious roots occur only on one side and at a wide angle (Figs 3, 7A, B). Leclercq and Banks (1962); 4, Hilton et al. (2003); 5, Xue and Hao (2008); 6, Leclercq (1951); 7, Andrews and Phillips (1968); 8, Cornet et al. (1976); 9, Hill et al. (1997); 10, Gensel (1973); 11, Hilton (1999); 12, Berry and Wang (2006); 13, Li and Hsü (1987);14, Taylor et al. (2009);15, Wang (2003); 16, Phillips and Galtier (2005); 17, Skog and Gensel (1980); 18, Knaus (1995); 19, Galtier (1988); 20, Stewart and Rothwell (1993); 21, Wang et al. (2014); 22, Wang and Liu (2015). ...
With the exception of angiosperms, the main euphyllophyte lineages (i.e. ferns sensu lato, progymnosperms and gymnosperms) had evolved laminate leaves by the Late Devonian. The evolution of laminate leaves, however, remains unclear for early-diverging ferns, largely represented by fern-like plants. This study presents a novel fern-like taxon with pinnules, which provides new insights into the early evolution of laminate leaves in early-diverging ferns.
Macrofossil specimens were collected from the Upper Devonian (Famennian) Wutong Formation of Anhui and Jiangsu Provinces, South China. A standard degagement technique was employed to uncover compressed plant portions within the rock matrix.
A new fern-like taxon, SHOUGANGIA BELLA GEN ET SP NOV: , is described and represents an early-diverging fern with highly derived features. It has a partially creeping stem with adventitious roots only on one side, upright primary and secondary branches arranged in helices, tertiary branches borne alternately or (sub)oppositely, laminate and usually lobed leaves with divergent veins, and complex fertile organs terminating tertiary branches and possessing multiple divisions and numerous terminal sporangia.
Shougangia bella provides unequivocal fossil evidence for laminate leaves in early-diverging ferns. It suggests that fern-like plants, along with other euphyllophyte lineages, had independently evolved megaphylls by the Late Devonian, possibly in response to a significant decline in atmospheric CO2 concentration. Among fern-like plants, planate ultimate appendages are homologous with laminate pinnules, and in the evolution of megaphylls, fertile organs tend to become complex.
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... As in Xinghangia, Eocladoxylon [19], Melvillipteris [6] and Protopteridophyton [20] show elongate and sometimes paired sporangia terminating in three-dimensionally dichotomous axes; Ellesmeris [18], Eocladoxylon, Melvillipteris and Rhacophyton possess basal aphlebiae; Ellesmeris, Eocladoxylon and Rhacophyton demonstrate clepsydroid xylem. However, all of these plants lack triseriate branching and some present quadriseriate branching; Rhacophyton has fertile organs paired at the branch base, and such arrangement occurs sometimes in Eocladoxylon; the fertile organs of Rhacophyton are very complex and unique, with pinnate segments, and those of Protopteridophyton are quadriseriate in arrangement and also complex. ...
... By contrast, in R. zygopteroides, the primary branches are helical on the main axis (probably) containing an actinostele [15]. Alternate branching and clepsydroid stele are also seen in Eocladoxylon [19] and now, in Xinhangia. As to the triseriate primary or secondary branches of Xinhangia, the unpaired branches and the common base of the paired branches are alternately attached. ...
Palaeozoic fern-like plants show great diversity in their morphology and/or anatomy. Within this group, a novel taxon, Xinhangia spina gen. et sp. nov., is now reported from the Upper Devonian (Famennian) Wutong Formation of Anhui Province, China. The primary and secondary branches are borne alternately and sometimes in a triseriate pattern. Spines are evident on the main axes or stems and on the primary branches. Vegetative ultimate appendages with recurved tips are alternate, usually dichotomous 1–2 times, and sometimes as an aphlebia located at the base of primary or secondary branches. Fertile ultimate appendages are alternate, usually dichotomous 1–2 times, and terminate in elongated and paired sporangia. The stele has a clepsydroid-like primary xylem with each end bearing a protoxylem strand. The secondary xylem surrounding the primary xylem illustrates uniseriate rays. With rare divisions in both the vegetative and fertile ultimate appendages, Xinhangia represents a morphologically primitive plant. It is of uncertain affinity at the class or order level. The stelar architecture suggests that the clepsydroid stele may not be emphasized in discussing the relationship among fern-like plants such as rhacophytaleans.
... axillar branching) is rare in Polypodiopsida except of Equisetidae, similarly to the presence of strobilus of metamorphosed appendages, hence very probable phylogenetic position of Stauropteridales is in this subclass. Morphologically closest group are the rhacophytaleans (Psilophytidae) with frequent quadriseriate branching, but unmetamorphosed fertile appendages (Andrews, Phillips 1968;Gensel 1973;Hilton 1999;Berry, Wang 2006;Xue, Basinger 2015). I have proposed the absence of an extensive metamorphosis of fertile appendages as a main criterion to distinguish the Lycopodiopsida from other vascular plants (Hrabovský 2020). ...
... It is believed that the most primitive order of ferns, Zygopteridales, has evolved from rhacophytes (Stewart, Rothwell 1993;Taylor et al. 2009). But the position of their fertile appendages does not match the position of fertile pinnules in Zygopteridales (Andrews, Phillips 1968;Gensel 1973;Galtier, Scott 1979;Hilton 1999;Galtier 2004Galtier , 2005Berry, Wang 2006;Xue, Basinger 2015) and the similarity between rhacophytes and zygopterids is comparable to their similarity with stauropterids caused by convergent evolution among related phylogenetic clades. Leaves of Zygopteridales grow from a phyllophore in pairs in a quadriseriate arrangement. ...
The possible relationships between microphyllous and megaphyllous leaves were presented in the previous part of this series. Leaves could be comprehended as single or branched microphylls or as compound systems of microphylls. The primitive forms of such compound systems, called appendages, led to the proposal of various phylogenetic trees based on their anatomy and morphology. This paper reevaluates the plesiomorphy of enigmatic Silurian or Devonian rhyniophytes and zosterophylls, as well as the predecessors of sphenophytes and modern ferns. According to the features of leaf morphology, there is no need to create hypothetical phylogenetic groups for fossil plants other than the recent groups revealed by molecular phylogeny. Thus, many polysporangiatophytes with unknown phylogenetic placement can be placed within sphenopsids, ophioglossids and true ferns.
... Their ultimate appendages were formed by undivided (Rhacophyton, Fig. 9.4) or dichotomously divided brachyblast (Eocladoxylon, Fig. 9.1; Melvillipteris, Fig. 9.2; Chlidanophyton, Fig. 9.3) bearing usually few-times divided archaeophylls (cf. Andrews, Phillips 1968;Gensel 1973;Hilton 1999;Berry, Wang 2006;Xue, Basinger 2015). Sometimes the appendages were transformed into sphenopteroid pinnules (Ellesmeris, Fig. 9.5; Hill et al. 1997). ...
... Fig. 9. Leaf evolution in psilophytes -rhacophytes: 1. Eocladoxylon minutum, sterile and fertile appendage; 2. Melvillipteris quadriseriata, sterile and fertile appendage; 3. Chlidanophyton dublinensis, fertile and sterile appendage; 4. Rhacophyton ceratangium, sterile appendages (pinnules); 5. Ellesmeris sphenopteroides, Sphenopteris-like pinnule. Modified after Berry, Wang (2006) (1), Xue, Basinger (2015) (2), Gensel (1973), Hilton (1999) (3), Andrews, Phillips (1968) (4) and Hill et al. (1997) (5). Author: M. Hrabovský. ...
Leaf evolution was discussed by many authors. There are two main theories about leaf origin. The telome theory is the most comprehensive. Another theory opposing the previous one is the enation theory. The telome theory was based on the "telomes" of rhyniophytes and the enation theory on the "enations" of zosterophyllophytes. We propose an adjusted theory based on appendages of cladoxylopsids, psilophytes and protolepidodendraleans. This presented theory is based on homological series found in these fossil groups. We recognize 12 groups of vascular plants, where leaves evolved independently. Three groups (Lycopodiidae-lycophytes, Archaeopterididae-archaeopterids and Psilophytidae-psilphytes) are morphologically very close and we classify them within the class Lycopodiopsida in a morphogenetic system. Finally, we adjust the morphological terminology for basic types of leaves.
... Among them, the Early Devonian (Pragian) euphyllophytes, e.g., Eophyllophyton (Hao 1988;Hao and Beck 1993;Hao et al. 2003), Yunia (Hao and Beck 1991), Celatheca (Hao and Gensel 1995), and Hedeia (Hao and Gensel 1998;Wang et al. 2002), display highly derived characters and cannot be readily assigned to known categories at class level. Middle Devonian (Givetian) euphyllophytes lack recognizable aneurophytalean progymnosperms, pseudosporochnaleans, and typical iridopteridaleans that are numerous in Laurussia and Gondwana (Berry and Wang 2006). Late Devonian (Famennian) euphyllophytes, e.g., the endemic Hamatophyton (Gu and Zhi 1974;Li et al. 1995;Wang et al. 2006) and Rotafolia (Wang et al. 2005), are widespread in Hubei, Jiangsu, Hunan, Anhui, and Zhejiang provinces. ...
... Anapaulia (Berry and Edwards 1996) has sporangia terminating recurved tips of ultimate appendages. Axial spines are uncertain in Metacladophyton (Wang and Geng 1997) but have been confirmed (Berry and Wang 2006), even on fertile axes (Wang and Lin 2007). In contrast, Tenuisa has subopposite or alternate laterals and sporangial pedicels, and it lacks axial spines. ...
Tenuisa frasniana gen. et sp. nov. is reported from the Late Devonian (Frasnian) Hunan Province of South China. Its axes are naked and narrow. Fertile stem is pseudomonopodial in branching and bears distichous lateral units. Fertile lateral units are subopposite and pseudomonopodial in the proximal part of stem, while they are alternate and isotomous two to four times in the distal part. They have tiny terminal sporangia that are paired and fusiform and that possess pedicels. Sterile ultimate units are dichotomous and terminate in tips recurving oppositely. Tenuisa resembles Psilophyton in pseudomonopodial fertile stem with alternate and dichotomous lateral units terminated by paired and vertically elongate sporangia. However, fertile lateral units are subopposite and pseudomonopodial on the basal part of stem, sporangial pedicels are present, and neither sporangial pairs nor sporangia themselves are twisted. This new plant differs from iridopteridalean cladoxylopsids mainly in the absence of whorled laterals and axial spines, and it differs from pseudosporochnalean cladoxylopsids in the absence of digitate lateral branches and the presence of sterile ultimate units with recurved tips. Because of these morphological differences and a lack of anatomical information, Tenuisa frasniana is currently left as incertae sedis within Euphyllophytina (sensu Kenrick and Crane).
... This character distinguishes the Iridopteridales from the Cladoxylopsida where, in both pseudosporochnalean and nonpseudosporochnalean 1093 taxa, branch vascular supplies are made up of several traces originating from several xylem ribs. Berry and Wang (2006a) also mentioned the lack of aphlebiae in all known Iridopteridales to date. ...
... The monospecific genus Metacladophyton (Wang and Geng 1997) is a Givetian taxon from Hubei Province, China, showing iridopteridalean characters according to Berry and Wang (2006a) and Wang and Berry (2006) but interpreted as a relative of the Pseudosporochnales by Cordi and Stein (2005). Metacladophyton tetraxylum consists of stems up to 1.5 cm wide that show long internodes separating whorls of two to seven first-order branches. ...
A new permineralized specimen of Polyxylon australe collected from the type locality at Barraba in New South Wales, Australia, represents a portion of stem showing a node in its proximal part. Analysis of its primary vascular system and pattern of branch trace emission indicates that the plant had a hierarchized architecture. The stem, ca. 2.5 cm wide, is radially symmetrical and bears a whorl of nine or 10 branches followed by a long internode. The bilateral symmetry of first-order branches, assessed from trace arrangement in individual branch bases, is a trait previously reported in three other nonpseudosporochnalean cladoxylopsid genera, Pietzschia, Cladoxylon, and Panxia. Xylem maturation in the stele of the new stem is exarch, but at node level, one mesarch strand of protoxylem differentiates around a cavity filled with thin-walled cells. The diagnosis of P. australe is emended, and the significance of architectural characters for distinguishing the Cladoxylopsida from the Iridopteridales is discussed. Polyxylon is the second and the best-known cladoxylopsid genus reported from the Devonian of Australia.
... Their comparisons remain valid and applicable to M. sonidia n. sp. Besides Melvillipteris, many other plant genera (e.g., Rhacophyton Crépin; Cephalopteris Nathorst; Protocephalopteris Ananiev; Ellesmeris Hill, Scheckler, and Basinger; Chlidanophyton Gensel; Eocladoxylon Koidzumi; Protopteridophyton Li and Hsü) were collectively included in the Rhacophytales (Hilton, 1999;Berry and Wang, 2006;Taylor et al., 2009), and the quadriseriate branching in these taxa may be a shared derived character (synapomorphy) (Xue and Basinger, 2016). However, taxonomic assignment of Melvillipteris to the Rhacophytales remains uncertain and requires further phylogenetic analyses. ...
The Silurian and Devonian plant fossil record is the basis for our understanding of the early evolution of land plants, yet our appreciation of early global phytogeographic evolution has been constrained by the focus of most studies on deposits from Europe, North America, and, more recently, South China. Devonian plants have been recorded rarely from northeastern China, and among previous records, few plants have been illustrated and formally described. In this article, megafossil plants representing a Late Devonian-aged (probably Famennian) flora are described from a locality at northern Sonid Zuoqi, Inner Mongolia, NE China. The flora includes Melvillipteris sonidia new species, Archaeopteris sp., and fragments of some other plants. The new plant shows main axes and two orders of lateral branches. The first-order branches of this plant show a typical zigzag appearance and are borne in pairs on main axes. Second-order branches are straight or slightly flexed, and are borne helically or alternately on first-order branches. Sterile ultimate appendages and fertile structures of M . sonidia n. sp. are borne alternately on second-order branches. An associated palynological assemblage, as well as U-Pb ages of detrital zircon grains from adjacent horizons, are also reported, indicating a Late Devonian age in accord with the megafossil plants. The present study contributes to our appreciation of the Devonian floristic diversity of the Xing'an Block, and, through our review of the record of early vascular plants from NE China, more broadly to the understanding of the mid-latitude vegetation of the Northern Hemisphere during the Late Devonian.
... Longostachys and several other Upper Devonian and Carboniferous upright lycopsids exhibit an unifacial vascular cambium. Unifacial vascular cambia also are found in Carboniferous calamitaleans and in the Upper Devonian Rhacophyton, which is of uncertain affinity and perhaps best treated as its own family, although similarities to some Iridopteridales as noted by Berry and Wang (2006) are intriguing. As mentioned, a limited amount of secondary xylem has been suggested to occur in some Devonian cladoxylopsids other than cf. ...
... Koidzumi (1943) rejected its assignment to the genus Protopteridium Krejči and created a new generic name, Eocladoxylon Koidzumi, for this plant. Berry and Wang (2006a) presented detailed information of its morphology and anatomy, based on specimens from Xichong, Zhanyi, Yunnan Province. ...
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The radiation of vascular plants during the mid to late Paleozoic has been considered one of the most important drivers of change in Earth's terrestrial environments. Non-marine deposits of the South China Block document plant diversification through the crucial Silurian and Devonian periods in a series of well-preserved fossil assemblages when this block occupied a paleoequatorial to low-latitude position and was isolated from the Laurussia paleocontinent. Significant plant fossils include the Pridoli and Early Devonian assemblages, from Yunnan and Sichuan provinces, southwestern China, and the Pragian Posongchong Flora from the Posongchong Formation of Wenshan, Yunnan. The Middle Devonian (Givetian) Haikou Formation and correlative strata supported diverse lycopsids and euphyllophytes, documenting landscapes with the first tree-like plants in South China. The Late Devonian Huangjiadeng, Xiejingsi and Wutong formations, particular the latter, preserve an abundance of lycopsids, fern-like plants, sphenopsids and seed plants, revealing complex plant communities. The taxonomic diversity in South China is characterized by a gradual increase from the Pridoli, with great diversification during the Pragian, a gap in the Emsian-Eifelian record, and a moderate increase in the Givetian and Frasnian, followed by a 2–3 times increase in the Famennian. Although the raw diversity pattern is somewhat obscured by different sampling intensity, the apparent increases during the Pragian and Famennian seem to be bona fide radiation events. Phytogeographically, the endemism of Early and Middle Devonian floras of South China has been supported by increasing paleobotanical data. The Late Devonian floras of South China began to share some, primarily arborescent species with other parts of the world. Axial diameter, leaf size, and multiple-character-based morphological disparity (mean pairwise dissimilarity) show stepwise evolutionary increase through the Devonian in parallel with the rise of taxonomic diversity. New integrative studies will further illuminate the terrestrialization process and the environmental impact of vascular plants.
... As the descendant of the aneurophytes, the spermatophytes were widespread in the Late Devonian (Famennian) of Laurussia. However, surprisingly, the aneurophytes have not been reported from South China [72,73]. There are now three genera of seed plants known from the Famennian of China or eastern Asia, i.e., Cosmosperma [2], Kongshania [3] and Yiduxylon (this paper). ...
Many ovules of Late Devonian (Famennian) seed plants have been well studied. However, because few taxa occur with anatomically preserved stems and/or petioles, the vascular system of these earliest spermatophytes is little understood and available data come mostly from Euramerica. There remains great controversy over the anatomical differentiation of Late Devonian and Carboniferous seed plant groups of Buteoxylonales, Calamopityales and Lyginopteridales. Protostele evolution of these early spermatophytes needs more research.
A new taxon Yiduxylon trilobum gen. et sp. nov. with seed plant affinities has been discovered in the Upper Devonian (Famennian) Tizikou Formation of Hubei Province, China. It is represented by stems, helically arranged and bifurcate fronds with two orders of pinnae and planate pinnules. Both secondary pinnae and pinnules are borne alternately. Stems contain a small protostele with three primary xylem ribs possessing a single peripheral protoxylem strand. Thick secondary xylem displays multiseriate bordered pitting on the tangential and radial walls of the tracheids, and has biseriate to multiseriate and high rays. A narrow cortex consists of inner cortex without sclerotic nests and sparganum-type outer cortex with peripheral bands of vertically aligned sclerenchyma cells. Two leaf traces successively arise tangentially from each primary xylem rib and they divide once to produce four circular-oval traces in the stem cortex. Four vascular bundles occur in two C-shaped groups at each petiole base with ground tissue and peripheral bands of sclerenchyma cells.
Yiduxylon justifies the assignment to a new genus mainly because of the protostele with protoxylem strands only near the periphery of primary xylem ribs, leaf trace origination and petiolar vascular supply structure. It shares many definitive characters with Calamopityales and Lyginopteridales, further underscoring the anatomical similarities among early seed plants. The primary vascular system, pycnoxylic-manoxylic secondary xylem with bordered pits on both tangential and radial walls of a tracheid and leaf trace divergence of Yiduxylon suggest transitional features between the early spermatophytes and ancestral aneurophyte progymnosperms.
... Axes of the latter plant were regarded to be nearly naked (Wang and Geng 1997, p. 95). However, the existence of the spines has been only mentioned (Berry and Stein 2000, p. 825) or confirmed (Berry and Wang 2006a). In our scrutiny of the figures (e.g., Wang and Geng 1997, pl. 1, fig. ...
The Late Devonian (earliest Frasnian) plant Metacladophyton ziguinum sp. nov. is described from Hubei Province, south China. Sterile main axes and first‐ and second‐order lateral axes possess linear spines that are sometimes dichotomous. Paired second‐order axes have a common base and occur oppositely and decussately on first‐order axes to form four vertical rows. With paired tips curving in opposite directions, sterile ultimate appendages are dichotomous, attached irregularly to first‐order axes and alternately/suboppositely to second‐order ones. Fertile ultimate appendages bifurcate equally three to five times and terminate in ovoid and erect sporangia in pairs. Metacladophyton ziguinum combines a protostele in the lateral axis and a dissected stele in the main axis. The primary xylem is U shaped and radially five ribbed in the protostele and consists of four V/U‐shaped or straplike ribs radially arranged in dissected stele. The mesarch primary xylem bears one or two protoxylem lacunae near the rib tip and is surrounded by secondary xylem containing uniseriate rays observed in transverse, tangential, and radial sections. The tracheid wall bears elliptical or circular bordered pits. In the protostele, a slightly ribbed column bearing an oval central hole originates from a nearly circular column via radial elongation of the primary xylem; through further radial elongation of the xylem and radial separation of the xylem between two adjacent ribs, the slightly ribbed column becomes a highly ribbed and U‐shaped column. In this process of stelar development, the secondary xylem occurs much earlier, gradually occupies the stelar center, and envelops the primary xylem. Metacladophyton ziguinum is assigned to Cladoxylopsida (sensu Berry and Stein), comprising Iridopteridales and Pseudosporochnales because of deeply bifurcate primary xylem ribs. In terms of a whole‐plant scenario of M. ziguinum, the dissected stele is suggested to be a synapomorphy of Cladoxylopsida, many members of which need better understanding in the morphological and/or anatomical characters. Based on anatomical evidence in M. ziguinum, one model is proposed explaining origination of the ribbed primary xylem, and an unequivocal secondary xylem is shown for first time in Cladoxylopsida. Metacladophyton ziguinum shows similarities with Iridopteridales in spiny axes, ultimate appendages with recurved tips, the protostele, permanent protoxylem strands, and larger metaxylem tracheids occurring along midplanes of ribs.
... determined by the index fish Bothriolepis and spore assemblages Geminospora lemurata-Cristatisporites triangulatus or Archaeozonotriletes variabilis- Cymbosporites magnificus (Lu & ouYang 1978; Cai 2000; tian & Zhu 2005). Besides Minarodendron cathaysiense (this study), other plants such as Psilophyton striatum Wang & BerrY, Eocladoxylon minutum (haLLe) KoiDZuMi and Rhipidophyton acanthum BerrY & Wang have been described from the Haikou Formation (corresponding to the upper part of the Xichong Formation) at the Xichong section in Zhanyi (Wang & BerrY 2001; BerrY & Wang 2006a, 2006b). These plants, together with those from other sections mainly in eastern Yunnan (e.g., Yuguangia ordinata hao et al. ...
Based on specimens from the Middle Devonian (Givetian) of Zhanyi County, Yunnan Province, China, we reinvestigate the morphology and anatomy of the protolepidodendralean lycopsid Minarodendron cathaysiense (Schweitzer & Cai) Li. New features of this plant include the stem up to 60 mm wide, axes dichotomizing as many as seven times, and microphylls with entire margins. Present anatomical characters conform to those known previously. The proportion of cortex area to stem (axis) area in cross section is proposed as an index to characterize the growth habit of the protolepidodendralean and isoëtalean lycopsids of the Middle Devonian to Carboniferous age. The thick stem and axes as well as high cortex proportion suggest that M. cathaysiense was probably a small tree. The Protolepidodendrales may have developed an arborescent habit in the late Middle Devonian.
... It is not certain, however, that the Sierra de Perijá terrane was already part of Gondwana in the Middle Devonian . Pseudosporochnaleans are unknown in North China (Cai & Wang 1995) and all previous records of Pseudosporochnus from South China have recently been dismissed (Berry & Wang 2006a). The closest genus found in South China is Rhipidophyton, which is common in Yunnan where it is represented by axes measuring up to 9 cm in diameter (Berry & Wang 2006b). ...
This paper reviews information on the Devonian trees that evolved in the euphyllophyte clade with special focus on the Middle Devonian Pseudosporochnales. The morphology of pseudosporochnalean trees shows analogies with that of extant tree ferns, including the possession of an adventitious root system of limited extent at the base of the trunk. Direct evidence on how these trees were constructed is scarce. We propose a growth model integrating information from younger representatives of the same class known to reach large diameters. According to this model, trunk width in its aerial part results from the large size of its primary body where living tissues are abundant, a condition reached early during growth. Secondary xylem contributes little to trunk diameter. This model sharply diverges from that of the Late Devonian archaeopteridalean trees characterized by an extended root system and where trunk diameter and mechanical support are achieved by the substantial development of secondary vascular tissues. These differences suggest that pseudosporochnalean trees may have had a lesser impact on Devonian environments than the Archaeopteridales. The important investment in living tissues in the Pseudosporochnales probably made them vulnerable to drought and cold.
... Thus, a close relationship between Denglongia and Rhacophyton is possible. Considering the possible relationship between Rhacophyton and 1329 XUE & HAO-NEW CLADOXYLOPSID FROM THE UPPER DEVONIAN OF SOUTH CHINA the Iridopteridales suggested by Berry and Stein (2000) and Berry and Wang (2006a), Rhacophyton might have evolved to a quadriseriate branching pattern from an iridopteridalean-type ancestor, but Denglongia maintained whorled branching, as in iridopteridaleans. The elongate and fusiform sporangia and the pinnate branching pattern in fertile structures of Denglongia also recall those of the aneurophytalean progymnosperms. ...
Denglongia hubeiensis gen. et sp. nov. is described from the Late Devonian Huangjiadeng Formation (Frasnian) of Hubei Province, South China. Main axes and two orders of lateral branches are recognized. The main axis is nodose and has a ridged surface, with a preserved length of up to 34 cm. Four to six first-order branches, sterile or fertile, are inserted at nodes of the main axis in a whorled pattern. Dense aerial roots occur at basal nodes of main axes, and sparse ones occur at some nodes of first-order branches. Some first-order branches bear only ultimate appendages; others bear ultimate appendages proximally and then in turn bear whorls of second-order branches distally, with an internode length of 40-60 mm. Sterile ultimate appendages are alternately or suboppositely borne on proximal portions of sterile first-order branches. One or two pairs of umbrella-shaped fertile structures are borne at the same position as sterile appendages but on fertile first-order branches. Second-order branches occur in whorls, with three or four at each node, and bear only sterile ultimate appendages. The fertile structure has an initial dichotomy that forms two sister components, each with lateral branches alternately arranged in a pinnate pattern. Each lateral branch dichotomizes several times, bearing small, fusiform sporangia in clusters of two to four on short branchlets along the inner side of the lateral branch. The plant is anisosporous. It is referred to a new genus and species, D. hubeiensis gen. et sp. nov. Its similarity to and divergence from iridopterid-cladoxylopsids, Rhacophyton, progymnosperms, and related plants are discussed. At present, Denglongia is assigned to Cladoxylopsida sensu lato in view of an iterative architecture and whorled organotaxis.
Shougangia bella from the Late Devonian (Famennian) of South China is a fern-like plant known for its morphology and now provided with anatomy and a reconstruction. Its stems contain a dissected stele with a four-ribbed and an elongate-curved primary xylem segments changing to three elongate and slightly curved segments. Primary branches have a dissected stele with three similar primary xylem segments as in stems. The primary xylem of the stems and primary branches is mesarch, and individual primary xylem segments bear peripheral protoxylem strands and are surrounded by secondary xylem. Shougangia is anatomically compared with fern-like plants, zygopterid ferns and early seed plants, verifying its uncertain affinity at class and order levels as suggested by morphology, or representing a new order within the Cladoxylopsida. On the basis of anatomy and branching pattern, it is emphasized that most fern-like plants appear evolutionarily closely related to iridopteridaleans. Secondary xylem is involved not only in mechanical support, but also more likely in enhancing water supply for fern-like plants including Shougangia. By the Late Devonian, besides the abrupt drop of atmospheric CO2 levels, the presence of secondary xylem may correlate well with the primary radiation of leaves (megaphylls) of euphyllophytes (e.g. fern-like plants, sphenopsids, progymnosperms and seed plants). © The Trustees of the Natural History Museum, London 2017. All rights reserved.
This book provides up-to-date coverage of fossil plants from Precambrian life to flowering plants, including fungi and algae. It begins with a discussion of geologic time, how organisms are preserved in the rock record, and how organisms are studied and interpreted and takes the student through all the relevant uses and interpretations of fossil plant. With new chapters on additional flowering plant families, paleoecology and the structure of ancient plant communities, fossil plants as proxy records for paleoclimate, new methodologies used in phylogenetic reconstruction and the addition of new fossil plant discoveries since 1993, this book provides the most comprehensive account of the geologic history and evolution of microbes, algae, fungi, and plants through time. * Major revision of a 1993 classic reference * Lavishly illustrated with 1800 images and user friendly for use by paleobotanists, biologists, geologists and other related scientists * Includes an expanded glossary with an extensive up-to-date bibliography and a comprehensive index * Provides extensive coverage of fungi and other microbes, and major groups of land plants both living and extinct.
Kunia venusta gen. et sp. nov. is reported from the late Middle Devonian (Givetian) Haikou Formation near Kunming City, Yunnan Province, China. This plant has three orders of naked axes that divide pseudomonopodially. The second-and third-order axes occur in a helix. Fertile appendages are distantly spaced and helically inserted to the third-order axis; they comprise equally dichotomous branches terminated by two clusters of paired and fusiform sporangia. Sterile appendages are dichotomous and distally recurved. A comparison is made with the basal euphyllophytes including the trimerophytes, cladoxylopsids, zygopterids, stauropterids, and some relevant genera of uncertain affinity. The new plant resembles them in dichotomous appendages with terminal elongated sporangia, but differs mainly in the three orders of pseudomonopodial axes bearing helical laterals. It is thus placed in the Euphyllophytina as incertae sedis. It is suggested that an evolutionary divergence in the branching pattern and appendage morphology might have occurred in the Middle Devonian euphyllophytes, that is, maintaining three dimensions versus yielding more or less planation.
Archaeopteris macilenta is one of the most widespread plants in the Late Devonian. Based on fossils from the Frasnian Huangjiadeng Formation, Yichang District of Hubei Province, for the first time we study in detail the anatomy of this progymnosperm plant in South China. Ultimate axes are protostelic with three xylem sympodia and lack secondary tissue. Penultimate axes are eustelic, bearing eight sympodia and a thin band of secondary xylem. Radially symmetrical sympodia of mesarch primary xylem produce traces of appendages in a spiral arrangement. Archaeopteris macilenta and A. halliana (A. roemeriana) are dominant in the Frasnian and Famennian, respectively. Comparisons with these two species from other tectonic plates indicate consistent stelar architectures. Global spread, continuous occurrence, and identical anatomy during the Late Devonian indicate that Archaeopteris survived the Frasnian-Famennian extinction event. In this time, endemic genera and cosmopolitan taxa, including Archaeopteris, suggest the palaeogeographic isolation of South China and certain associations with other plates.
: New materials from the Upper Devonian (Famennian) Wutong Formation of Chizhou District, Anhui Province, South China, allow description of fertile and sterile characters of Archaeopteris halliana. This plant has penultimate axes attached by sterile leaves and paired ultimate branches in the same ontogenetic spiral. Sterile leaves are narrowly cuneate in shape and bear distal margins dissected deeply. These leaves are spirally arranged on sterile ultimate axes. Non-laminated sporophylls occur spirally on the ultimate axes and bifurcate once or twice. Elongate sporangia with longitudinal dehiscence are borne adaxially below or above the dividing points of the sporophylls. Despite the leaf shape resembling that of Archaeopteris macilenta, our plant is assigned to A. halliana because of its non-laminated sporophylls. Fertile characters should be given priority or enough consideration in identifying species of Archaeopteris.
A previous study of the Late Devonian cladoxylopsid Denglongia hubeiensis Xue et Hao provided a detailed morphological description, while new material from the type locality of the Huangjiadeng Formation, Hubei Province, China, reported here reveals details of anatomy. Main axes are actinostelic in transverse sections, showing a primary xylem column with five or six xylem ribs separated by deep embayments. First-order axes have a deeply ribbed primary xylem column with four xylem ribs. Each stelar rib has two permanent, mesarch protoxylem strands near its periphery. Tracheids interpreted as protoxylem show annular or helical thickenings. Metaxylem tracheids have scalariform and elliptical bordered pits. Anatomically, Denglongia is more similar to the iridopteridaleans than to other plants in the actinostele, the peripheral protoxylem strands, the disintegration of protoxylem tracheids, and the pitting pattern of metaxylem tracheids. The phylogeny of the Cladoxylopsida was evaluated by parsimony and Bayesian cladistic analyses. The results showed that the Pseudosporochnales constitute a very robust monophyletic group supported by a suite of characters: the presence of arborescence; digitate branching; straight tips of sterile ultimate appendages; dissected primary xylem; elliptical to strap-shaped primary xylem strands; and sclereids in the cortex. The monophyly of the Iridopteridales is questioned in that the previously suggested defining characters, whorled branching and peripheral protoxylem strands, are considered more plesiomorphic in the cladistic context. The relationship between the iridopteridaleans and the sphenophyllaleans is weakly supported. The Bayesian analysis recognized a tentative "iridopteridalean-based group," in which the iridopteridaleans, Denglongia, Metacladophyton Wang et Geng, Polypetalophyton Geng, and their probable relatives are nested within an unresolved polytomy.
Over the past 10 years, significant progress has been made in our understanding of late Mid Devonian floras of Yunnan Province, China. Based on new collections and a restudy of existing specimens, most of the old taxa have been emended, and some new taxa described. The late Mid Devonian Xichong flora of Yunnan is dominated by lycopsids, including prelycopsids, homosporous and herbaceous protolepidodendrids. The ‘fern’-like and cladoxylopsid plants are important and are mainly endemic. A few small plants have also been reported. The Xichong flora is divided into two ecological levels: small tree and ground cover levels. The palaeoclimate of late Mid Devonian Yunnan belonged to the tropical zone. There are noticeable differences between the fossil plants of Yunnan and those of the late Mid Devonian in Laurussia and Venezuela. The Xichong flora is a special, endemic flora in a palaeogeographically isolated tropical area, controlled by local palaeoclimate. The sequence of floras developed in pre-Carboniferous time in South China includes the Posongchong (Pragian), the Xichong (late Givetian) and the Wutung (late Famennian) floras. These floras are treated as pre-Cathaysian floras. Further work is required to establish how much influence these pre-Cathaysian floras had in the Carboniferous-Permian development of the Cathaysian Flora. Copyright © 2007 John Wiley & Sons, Ltd.
A new plant is described on the basis of compression fossils from the Xichong Formation, Middle Devonian (upper Givetian) of Yunnan Province, China. The plant has a stout stem (up to 90 mm diameter). Lateral sterile branches are ramified in a series of perpendicular dichotomies (proximally close and ‘digitate’), terminating in recurved tips, and lack appendages. Fertile branches are unramified, and have fertile appendages attached in a helical pattern. The fertile appendages are composed of a central axis to which is attached proximally a pair of sporangia, and which distally becomes flattened or broadened with a shallow terminal dissection and two pairs of sporangia attached on each side of the dissection in a fan-like arrangement. Sterile and fertile branching systems are not found in organic connection, but are inferred to belong to the same plant both because of close association and because both sterile branching systems and fertile appendages bear characteristic narrow spines. Although the affinities of this plant are not certain, we assign it to Cladoxylopsida on the basis of the ‘digitate’ branching from which we infer an underlying highly dissected vascular system. However the plant lacks many characteristics of the best defined group of Middle Devonian Cladoxylopsida, Pseudosporochnales, including sterile appendages, straight tips and distinctive sclerid nests within the cortex. After consideration, previous records of Pseudosporochnus in South China are discounted as the digitate branches featured probably represent our new plant. The new plant, named Rhipidophyton acanthum Berry et Wang gen. et sp. nov, further highlights the phytogeographic isolation of the Yunnan Middle Devonian flora, and suggests greater diversity of Middle Devonian cladoxylopsid bauplans than previously recognised.
Plant fossils from the Avon Gorge originally identified asRhacophytonsp. have been subjected to a detailed morphological study incorporating examination of both previously known material and new specimens. A single taxon,Chlidanophyton dublinensis, dominates the assemblage accounting for over 90% of the fossils encountered. Other plant organs identified include dispersed acupulate preovules and five less frequently occurring organs of which four are of unknown affinities; the leaf genusPlatyphyllum, Alicornopterissptwo kinds of novel and frequently dichotomizing branching structures and the spermatophyte synangiumTelangiopsis.Possible whole plant relationships between the components of the fossil assemblage are discussed and the stratigraphic, systematic and evolutionary position of the component taxa are considered.
An investigation of the fossil plant Polypetalophyton wufengensis Geng ex Hilton, Geng et Kenrick provides new data on an early woody member of the Late Paleozoic group Cladoxylopsida. The morphology and anatomy of the lateral branch system have been studied in detail. Branches were produced in an irregular helix, but ultimate appendages were borne in a pinnate arrangement on a frondlike system. Vegetative "pinnules" were dichotomous and planar (Sphenopteridium-type), whereas fertile "pinnules" were decussately branched and bore fusiform sporangia terminally. Anatomically, Polypetalophyton is unusual because it has a stele that consists of several primary vascular segments, each of which consists of tracheids and parenchyma surrounded by wood comprising radially aligned tracheids with ray-like slits. Polypetalophyton is clearly most closely related to the extinct Cladoxylopsida, which is a poorly understood group of considerable phylogenetic significance. Comparisons are made with Pseudosporochnales and Iridopteridales, and it is argued that Polypetalophyton resembles most closely the former. Polypetalophyton differs from the handful of well-known members of this group in possessing radially aligned xylem and in lacking sclereid nests in the stem cortex. It is also unique in its plagiotropic pinnate frondlike branching system, which we interpret to be the functional equivalent of a leaf or frond. Polypetalophyton represents the first evidence of Sphenopteridium-type foliage occurring within Cladoxylopsids and demonstrates that this kind of foliage has evolved independently within at least three distinct plant clades: Zygopterids, Cladoxylopsids, and seed plants. The name Polypetalophyton wufengensis is validated through the designation of a type specimen.
A reinvestigation of the permineralized axis Iridopteris eriensis Arnold, from type and new material, was conducted as part of a comprehensive study of all members of the Iridopteridineae of Arnold. The information presented here suggests that Iridopteris was a highly distinctive Middle Devonian plant with (1) a five-ribbed, mesarch, primary xylem column and apparent bilateral symmetry; (2) simple protoxylem strands, or cavities representing protoxylem strands, grouped in multiples near the tips of primary xylem ribs; (3) traces of two distinct sizes; (4) whorled order of trace departure; (5) metaxylem tracheids with circular to elongate elliptical bordered pit pairs with elliptical apertures; and (6) a distinct boundary between stele and cortex apparently comprised of a single layer of cells with dark materials in their lumina. Accumulating evidence suggests that a taxonomically distinct group of Middle and lower Upper Devonian plants has only partially been recognized. The Iridopteridales is here establ...
from which leaf traces arise in a spiral sequence. The anatomy of the "rachis" and of the "'pinnae" is shown to be similar to that of the stem, Callixylon, which bore these "fronds." Branching, epidermal pattern and stomates are described for the spirally arranged leaves (fertile pinnules). Attachment and dehiscence of sporangia as well as their stomates are reported. Archaeopteris is retained in the Class Progymnospermopsida which includes plants with gymnospermous anatomy and pteridophytic reproduction. It is suggested that Actinopodium, Svalbardia and Siderella are related closely to Archaeopteris and that this group of genera shows evolutionary stages in webbing of leaves and planation of branch systems. The opportunities for ontogenetic studies of the arborescent genus Archaeopteris are pointed out.
The first permineralized Devonian plant fossil is reported here from the Middle or lowermost Upper Devonian of western Venezuela. Two orders of branching plus dichotomous ultimate appendages are known from compressions. A branch of the first order contains a mesarch actinostele with six primary xylem ribs, each with a protoxylem strand near the rib tip (peripheral edge). Compressions of first-order branches demonstrate three equally spaced lateral organs (higher-order branches and dichotomous ultimate appendages) attached in whorls, with every other whorl displaying laterals placed in identical orientations and intermediate Whorls with laterals offset exactly halfway between. The permineralized specimen partly confirms the presence of whorls and indicates that vascular traces are derived from every other primary xylem rib in each whorl, with intervening ribs producing traces in whorls above and below. Second-order branches have only ultimate appendages that are attached in a nonwhorled, three-dimensional, or alternate arrangement. Sterile ultimate appendages dichotomize up to six times and terminate in recurved tips. Fertile ultimate appendages have paired sporangia distally; these sporangia are often upright but are otherwise similar to sterile examples. The stelar anatomy demonstrates an iridopteridalean affinity for these plants, resembling Arachnoxylon kopfii Read in arrange ment and number of xylem ribs although it is smaller in size. Among iridopteridaleans, the branching pattern and mode of trace departure is unique, and we therefore name the plant Compsocradus laevigatus gen. et sp. nov.
Small plant fragments previously attributed to Dimeripteris cornuta SCHWEITZER and CAI and new specimens are described from the Middle Devonian (Givetian) Xichong Formation of Wuding, Yunnan Province, southwest China. A predominantly trifurcate branching pattern is recognized in lower orders of branching. Erect fusiform sporangia are borne in pairs terminally on a short pedicel on up to three times dichotomously-branching fertile unit. The beaked tips of the paired sporangia point outwards. This plant is distinguished from known plants by the trifurcate branching pattern and sporangia morphology, but is of problematic affinity. The plant is named Tauritheca cornuta (SCHWEITZER and CAI) WANG and BERRY nov. gen. and nov. comb.
Compression fossils of a new plant, Anapaulia moodyi Berry et Edwards, gen. et sp. nov., are described from the Middle or Upper Devonian of western Venezuela. The main novel characteristic of this plant is that the monopodial main axis has both large second-order axes as well as smaller dichotomizing branches inserted in a predominantly whorled arrangement, the whorls being separated by long internodes. Third-order axes and small fourth-order axes are borne in compressed helices and helices. Small ultimate branching systems, which dichotomize up to four times, are borne on the third- and fourth-order axes in helices and compressed helices. Elliptical sporangia are borne upon the recurved tips of ultimate branching systems otherwise similar to the sterile examples. The entire plant up to the second or third divisions of the ultimate branching systems is covered with fine spines. The nature of the whorled arrangement of branching in the first-order axes sets the plant apart from the Trimerophytina and other contemporary and earlier land plants. A close comparison can be drawn with permineralized stems from the Middle Devonian of North America belonging to Iridopteridales Stein, which show anatomical traits which may correspond to the branching patterns found in Anapaulia. There are morphological similarities to compression fossils of the iridopteridalean Ibyka Skog et Banks, for which both permineralizations and a limited amount of compression material was described. Anapaulia is thus tentatively assigned to the Iridopteridales.
Petrifactions of Rhacophyton ceratangium were collected from the Upper Devonian Hampshire Formation near Valley Head, West Virginia. The approximate age of the locality is latest Cassadagan to earliest Bradfordian, equivalent to the upper middle Famennian (Fa2c) in European terminology. Ground thin sections were prepared from the limonitized petrifactions, and a pyritized specimen was prepared and examined under the SEM. The rachides of R. ceratangium were found to be bipolar or clepsydroid in cross-section, with secondary xylem present or absent. Vascular rays in the secondary xylem are demonstrated in this species for the first time. Pitting of tracheids was found to be scaliformly bordered. Emission of pinna traces was found to be etapterid. Peripheral loops, when present, were filled with parenchyma, or replaced by a decay gap or lacuna. Pinna traces bifurcate at an early stage in their development, and the clepsydroid anatomy is repeated in at least one order of branching. R. ceratangium was compared to the other anatomiccally known species within the genus.
Certain characters of the branching patterns of Hyenia vogtii Høeg (Pseudosporochnus vogtii (Høeg) Schweitzer) from the Middle Devonian (Givetian) of Spitsbergen, Svalbard, are clarified. Branching is predominantly whorled. In a whorl, dichotomous appendages form the majority of the subtending organs, but the position of an appendage may be taken by a branch. This pattern is typical of plants of the Middle and Late Devonian group Iridopteridales and fits within the generic circumscription of the genus Ibyka Skog and Banks to which it is transferred under the name Ibyka vogtii (Høeg) Berry comb. nov.
A new plant is described from the Middle Devonian (Givetian) Xichong Formation of Wuding, Yunnan Province, Southwest China. The plant has small axes covered in deltoid spines and a predominantly dichotomous (anisodichotomous) pattern of branching. Elongate sporangia with small distal spines are carried terminally in clusters on short branches which have a number of close distal dichotomies. These plants, superficially similar to the predominantly Lower Devonian genus Psilophyton, can be distinguished from it by the anisodichotomous nature of the lateral branching systems, by the spiny extensions to the sporangia and by the details of the sporangial attachments. The plant is named Tsaia denticulata Wang et Berry gen. et sp. nov.
Eight structurally preserved specimens originally called Cladoxylon onteorense nom. nud. Hueber 1959, from Hensonville, New York, Cladoxylon dichotomum nom. nud. Hueber 1960 from East Ashland, N.Y., and Cladoxylon hueberi Matten 1974 from East Ashland and Cairo, N.Y., are analyzed in detail for their morphological and systematic significance. The type of C. hueberi from East Ashland, by far the most important specimen, provides the first opportunity in any Devonian member of the Cladoxylopsida for a realistic three-dimensional assessment of the primary xylem system. A main axis contains a highly dissected primary xylem system with 40–50 longitudinally anastomosing primary xylem segments. Distally, the main axis dichotomizes producing two equal branches with 20–25 xylem segments each. The outermost primary xylem consists of a system of radially oriented tracheid plates variously interconnected toward the inside, each with a conspicuous protoxylem strand near the xylem periphery. Traces to densely and three-dimensionally, but not helically, arranged lateral appendages depart singly or in groups of two or three from one to three adjacent peripheral-radial xylem plates. Although direct evidence on the external morphology of lateral appendages is not preserved, many trace groups exhibit conspicuous bilateral symmetry consistent with the interpretation of planate lateral appendages similar to those described for Pseudosporochnus nodosus. Other trace groups may indicate more three-dimensional lateral appendages. One sub-opposite pair of clepsydroid traces is borne at right angles to, and in obvious relationship with, the dichotomy of the main axis. Cortex is heterogeneous, consisting of thin-walled parenchyma with embedded clusters of sclereids and thick-walled parenchyma. These clusters appear responsible for a regular pattern of bumps or pits in compressed regions of the specimen and are closely comparable to those observed in Pseudosporochnus nodosus. A systematic analysis, attempting to view fragmentary evidence from both compressions and permineralizations in a single coherent framework, leads us to hypothesize assignment of the East Ashland and Hensoville specimens to the genus Pseudosporochnus. Although supported by the evidence, the hypothesis of assignment is by no means proven. We propose it, however, because we think that advancing systematic hypotheses conspicuously at risk of being refuted by additional observation promotes far greater understanding than taking an agnostic stance toward systematics implied by the use of “form” taxa. We further clarify our position by suggesting specific observations likely to be made from fossil specimens that might refute our hypothesis.
A new fern-like fossil plant is described from the lower Upper Devonian of southern Ellesmere Island, Canadian Arctic Archipelago. The plant occurs in an Archaeopteris-dominated flora preserved in the Nordstrand Point Formation (Mid-Late Frasnian) near Bird Fiord. The plant has a pinnate vegetative system with three branch orders and laminate sphenopteroid pinnules. Primary pinnae usually diverge from the main axis in distichous pairs (quadriseriate), but can depart singly (biseriate). Each primary pinna bears a basal catadromic aphlebia. Anatomically, the plant exhibits a mesarch, bipolar protostele that is ribbon- to clepsydropsoid-shaped in the main axis. Primary pinna traces are also initially bipolar and crescent-shaped, but may become four-ribbed before dividing into a pair of bipolar traces. The morphology and anatomy of this plant are nongymnospermous and are most similar to Zygopteridales (particularly Rhacophytaceae and Zygopteridaceae). The Frasnian age of Ellesmeris shows that laminated foliage had evolved in some zygopterid ferns much earlier than previously recognized. The Sphenopteris-like pinnules of Ellesmeris indicate the need for caution when attributing such a convergent foliar design to other plant groups, such as the Devonian gymnosperms.
Typescript. Thesis (Ph. D.)--University of Connecticut, 1972. Includes bibliographical references.
Procedures are presented for the preparation of fine-polished surfaces of pyrite permineralizations, and demineralized thin-sections of limonite permineralizations. A major new feature in both procedures involves the re-embedding in plastic of individual cut sections in order to promote stability of the often crumbly material during further preparation. Pyrite sections are kept flat during polymerization of the plastic by means of a binder clip press. The technique for limonite permineralizations is characterized by the use of plastic not only for re-embedding individual sections but also for adhesion of sections to glass slides. Following this, sections are ground thin and demineralized with hydrochloric acid. We strongly recommend use of the thin-section technique for all studies utilizing limonite permineralizations because this method permits a much greater resolution of detail than is possible with other methods. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/24068/1/0000320.pdf
New observations on trunks of Pseudosporochnus nodosus Leclercq et Banks (Cladoxylopsida) from the Middle Devonian (upper Eifelian) of Goé, Belgium, show for the first time the presence of significant contiguous scars on their surfaces. The morphology of these scars corresponds to the morphology of the bases of first-order, digitately divided branches characteristic of the genus. We therefore reconstruct Pseudosporochnus with a sturdy trunk bearing densely and acutely inserted lateral branches capable of abscission at their base. We reject previous interpretations of Pseudosporochnus that do not include lateral branching of the trunk. In proposing an architectural model for Pseudosporochnus, we believe it to apply to other mainly Middle Devonian plants that we place in Pseudosporochnales, Calamophyton Kräusel et Weyland, Lorophyton Fairon-Demaret et Li, and Wattieza Stockmans. The largest trunks bearing branch scars that we can now positively identify as Pseudosporochnus from Goé have a diameter of 13 cm and indicate a moderately sized tree.
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