Figure 4 - uploaded by D. D. Sokoloff
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Potamogeton lucens. Inflorescence tip with four flowers in the uppermost whorl. Two flowers of the uppermost whorl have quite reduced structure. One of them (lower-right in the figure) has one tepal and one carpel (small circle). None of the flowers of the final whorl possess subtending bracts.
Source publication
Quantitative and qualitative data on variation of inflorescence tip in two species of Potamogeton are presented. Partial inflorescences of both species are spikes. Flowers in spikes are arranged in alternating whorls. In the lower and middle part of an inflorescence, most flowers have a structure that is typical for Potamogeton, i.e., four tepals,...
Contexts in source publication
Context 1
... we found many male flowers, female flowers were almost completely absent in the material examined; we found only one example of a female flower (see Fig. ...
Context 2
... However, the presence and number of bracts do not represent the final argument in deciding whether a structure (1) is really terminal and (2) really represents a flower. Our doubts are due to the following observations. We found a number of inflorescences of P. lucens where none of three flowers of the final whorl was subtended by a bract (Fig. 4) or where only one of three flowers of the final whorl was subtended by a bract (Fig. 7). Sometimes (though very rarely) we failed to find subtending bracts in all flowers of an ...
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Citations
... In Potamogeton, there are usually four tepals, four stamens on the radii of tepals and four carpels alternating with tepals. Less common, along with other types, are flowers with three tepals and three stamens on the same radii, alternating with three carpels (Charlton & Posluszny 1991, Lock et al. 2009). All interpretative problems outlined above for A. paucitepala can be also applied for Potamogeton. ...
The genus Aspidistra (Asparagaceae) shows strong variation of flower groundplan. We add further evidence of this variation describing a new species, Aspidistra paucitepala from southern Vietnam that has flowers with 2-4 tepals, 2-4 stamens and a gynoecium with unilocular ovary. Bisexual flowers with three tepals and three stamens are extremely rare among monocots with biotic pollination. Compared with typical trimerous pentacyclic monocot flowers, they can be either interpreted as trimerous and tricyclic or as 1.5-merous (at least in perianth and androecium) and pentacyclic. Both interpretations imply floral features unusual for 'higher' Asparagales. Aspidistra paucitepala resembles recently described A. brachystyla from northern Vietnam in narrow funnel-shaped to nearly tubular perianth with very small lobes and short cylindrical pistil with stigma located below the level of anthers. As species of the taxonomically diverse genus Aspidistra are frequently observed in the field without reproductive structures and cannot be properly identified, a need for DNA barcoding approach is obvious. We present preliminary data showing that plastid psbA-trnH and nuclear 5SNTS regions could be useful for DNA barcoding of Aspidistra.
... Racemose inflorescences of early-divergent monocots (Acorales and Alismatales) show a range of variation in inflorescence tip structure (Lehmann and Sattler, 1992;Buzgo and Endress, 2000;Buzgo et al., 2004Buzgo et al., , 2006Sokoloff et al., 2006;Lock et al., 2009). In addition to typical open and closed conditions, they include a condition with terminal flower-like structure of unstable morphology that could be variously interpreted in terms of disturbance of the flowerforming programme or amalgamation of the uppermost lateral flowers. ...
... These crucial features of inflorescence architecture are sometimes not consistent, even at the generic level. Scheuchzeria (Scheuchzeriaceae), Posidonia (Posidoniaceae), most Tofieldia species (Tofieldiaceae) and some Potamogeton species (Potamogetonaceae) all belong to the group with consistently bracteate inflorescences (Sattler, 1965;Posluszny and Sattler 1974;Posluszny, 1981Posluszny, , 1983Tomlinson, 1982;Sun et al., 2000;Remizowa et al., 2006aRemizowa et al., , 2013Sokoloff et al., 2006;Lock et al., 2009). Tofieldia pusilla, Araceae, Aponogetonaceae, Juncaginaceae, Ruppiaceae, some Potamogetonaceae and possibly Zosteraceae (Alismatales) as well as Acorus (Acorales) are characterized by non-bracteate inflorescences, or at least the FSBs are not visible as separate organs (Uhl, 1947;Sattler, 1973, 1974;Singh and Sattler, 1977;Lieu, 1979;Soros-Pottruff and Posluszny, 1995a, b;Mayo et al., 1997;Buzgo and Endress, 2000;Buzgo, 2001;Barabé et al., 2002Barabé et al., , 2011Remizowa and Sokoloff, 2003;Buzgo et al., 2004Buzgo et al., , 2006Remizowa et al., 2006aRemizowa et al., , 2013Lock et al., 2011;Lock, 2012). ...
... In Potamogeton species that differ from Triglochin in possessing a whorled rather than spiral flower arrangement (see Charlton, 1980;Lock et al., 2009), the pedicel bundle splits in the node of the inflorescence axis or slightly below it to form two branches that fuse with the nearest bundles of the inflorescence axis. Taxa with distichous phyllotaxy (Potamogeton densus, Ruppia and Posidonia) demonstrate an unusual pattern of vasculature of the inflorescence axis that involves fusion between the pedicel trace and stem bundles in a radial rather than tangential plane. ...
Racemose inflorescences (spikes, racemes and spadices) with flower-subtending bracts either absent or superficially inconspicuous are common among early-divergent monocots classified in the orders Alismatales and Acorales. This bractless condition contrasts with some other monocot orders such as Liliales, Petrosaviales and Dioscoreales, in which flower-subtending bracts are normally present. Two different patterns of bract reduction occur among early-divergent monocots (see also Posluszny and Sattler, 1973; Lieu, 1979; Charlton, 1981; Posluszny, 1981; Buzgo and Endress, 2000; Buzgo, 2001; Remizowa and Sokoloff, 2003; Buzgo et al., 2006; Remizowa et al., 2006): (1) bract suppression leading to formation of a cryptic bract and (2) formation of a single ‘hybrid’ organ (instead of two distinct abaxial organs situated on the same radius) by overlap of developmental programmes of the flower-subtending bract and the first abaxial organ formed on the floral pedicel. In the latter case, a flower-subtending bract is absent as a separate organ, but its features are partially expressed in the hybrid organ. The second pattern could also be interpreted without involving a hybrid organ concept; for example, by assuming that the outer abaxial perianth member is lost and replaced by a flower-subtending bract developing in an unusual position.
... Racemose inflorescences of early-divergent monocots (Acorales and Alismatales) show a range of variation in inflorescence tip structure (Lehmann and Sattler, 1992;Buzgo and Endress, 2000;Buzgo et al., 2004Buzgo et al., , 2006Sokoloff et al., 2006;Lock et al., 2009). In addition to typical open and closed conditions, they include a condition with terminal flower-like structure of unstable morphology that could be variously interpreted in terms of disturbance of the flowerforming programme or amalgamation of the uppermost lateral flowers. ...
... These crucial features of inflorescence architecture are sometimes not consistent, even at the generic level. Scheuchzeria (Scheuchzeriaceae), Posidonia (Posidoniaceae), most Tofieldia species (Tofieldiaceae) and some Potamogeton species (Potamogetonaceae) all belong to the group with consistently bracteate inflorescences (Sattler, 1965;Posluszny and Sattler 1974;Posluszny, 1981Posluszny, , 1983Tomlinson, 1982;Sun et al., 2000;Remizowa et al., 2006aRemizowa et al., , 2013Sokoloff et al., 2006;Lock et al., 2009). Tofieldia pusilla, Araceae, Aponogetonaceae, Juncaginaceae, Ruppiaceae, some Potamogetonaceae and possibly Zosteraceae (Alismatales) as well as Acorus (Acorales) are characterized by non-bracteate inflorescences, or at least the FSBs are not visible as separate organs (Uhl, 1947;Sattler, 1973, 1974;Singh and Sattler, 1977;Lieu, 1979;Soros-Pottruff and Posluszny, 1995a, b;Mayo et al., 1997;Buzgo and Endress, 2000;Buzgo, 2001;Barabé et al., 2002Barabé et al., , 2011Remizowa and Sokoloff, 2003;Buzgo et al., 2004Buzgo et al., , 2006Remizowa et al., 2006aRemizowa et al., , 2013Lock et al., 2011;Lock, 2012). ...
... In Potamogeton species that differ from Triglochin in possessing a whorled rather than spiral flower arrangement (see Charlton, 1980;Lock et al., 2009), the pedicel bundle splits in the node of the inflorescence axis or slightly below it to form two branches that fuse with the nearest bundles of the inflorescence axis. Taxa with distichous phyllotaxy (Potamogeton densus, Ruppia and Posidonia) demonstrate an unusual pattern of vasculature of the inflorescence axis that involves fusion between the pedicel trace and stem bundles in a radial rather than tangential plane. ...
Background
Understanding and modelling early events of floral meristem patterning and floral development requires consideration of positional information regarding the organs surrounding the floral meristem, such as the flower-subtending bracts (FSBs) and floral prophylls (bracteoles). In common with models of regulation of floral patterning, the simplest models of phyllotaxy consider only unbranched uniaxial systems. Racemose inflorescences and thyrses offer a useful model system for investigating morphogenetic interactions between organs belonging to different axes.ScopeThis review considers (1) racemose inflorescences of early-divergent and lilioid monocots and their possible relationship with other inflorescence types, (2) hypotheses on the morphogenetic significance of phyllomes surrounding developing flowers, (3) patterns of FSB reduction and (4) vascular patterns in the primary inflorescence axis and lateral pedicels.Conclusions
Racemose (partial) inflorescences represent the plesiomorphic condition in monocots. The presence or absence of a terminal flower or flower-like structure is labile among early-divergent monocots. In some Alismatales, a few-flowered racemose inflorescence can be entirely transformed into a terminal 'flower'. The presence or absence and position of additional phyllomes on the lateral pedicels represent important taxonomic markers and key features in regulation of flower patterning. Racemose inflorescences with a single floral prophyll are closely related to thyrses. Floral patterning is either unidirectional or simultaneous in species that lack a floral prophyll or possess a single adaxial floral prophyll and usually spiral in the outer perianth whorl in species with a transversely oriented floral prophyll. Inhibitory fields of surrounding phyllomes are relevant but insufficient to explain these patterns; other important factors are meristem space economy and/or the inhibitory activity of the primary inflorescence axis. Two patterns of FSB reduction exist in basal monocots: (1) complete FSB suppression (cryptic flower-subtending bract) and (2) formation of a 'hybrid' organ by overlap of the developmental programmes of the FSB and the first abaxial organ formed on the floral pedicel. FSB reduction affects patterns of interaction between the conductive systems of the flower and the primary inflorescence axis.
... In all genera of Zosteraceae, the spadix axis contains three parallel bundles but only the lateral ones produce branches to supply the fl oral organs ( Uhl, 1947 ) in the generative axes that ultimately develop fl owers. For example, fl owers of Triglochin are arranged spirally along the raceme axis, whereas in Potamogeton the distichy of the vegetative leaves is followed by a whorled fl oral arrangement ( Sattler, 1965 ;Posluszny and Sattler, 1974a , b ;Posluszny, 1981 ;Charlton, 1981 ;Tomlinson, 1982 ;Sun et al., 2000 ;Lock et al., 2009 ;Remizowa et al., in press ). ...
Unlabelled:
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Premise of the study:
The predominantly aquatic order Alismatales displays a highly variable flower groundplan associated with a diverse range of developmental patterns. We present the first detailed description of flower anatomy and development in Posidonia, the sole genus of the seagrass family Posidoniaceae. Existing accounts provide conflicting interpretations of floral and inflorescence structure, so this investigation is important in clarifying morphological evolution within this early-divergent monocot order. •
Methods:
We investigated two species of Posidonia using light microscopy and scanning electron microscopy. Our observations are interpreted in the framework of a recent molecular phylogeny. •
Key results:
Partial inflorescences are bracteate spikes, which are arranged into a botryoid or a panicle. The flowers are perianthless. The gynoecium is monomerous with the ventral carpel side oriented abaxially. The carpel contains a single pendent bitegmic ovule with a nucellus and long chalaza, both extending along the carpel wall. The ovule develops an integumentary outgrowth. Each flower is supplied by a vascular bundle, whereas the flower-subtending bracts are nonvascularized. •
Conclusions:
Our data support a racemose interpretation for the partial inflorescence of Posidonia and the presence of flower-subtending bracts. In common with some other Alismatales, Posidonia has simultaneous development of the flower and its subtending bract and loss of the bract vascular supply accompanied by innervation of the flower by a single vascular strand. The unusual carpel orientation could be an evolutionary reduction of a formerly tricarpellate gynoecium. The ovule of Posidonia is campylotropous and unusual within Alismatales in possessing an integumentary outgrowth.
... Studies on the floral morphology of Potamogeton were devoted to define the floral unit as a true flower or a reduced inflorescence (Kunth, 1841;Miki, 1937;Uhl, 1947;Sattler, 1965;Singh, 1965;Posluszny andSattler, 1973, 1974). More recently, Rudal (2003) suggested that the pseudanthium of Potamogeton is an intermediate structure between a flower and an inflorescence, while Lock et al. (2009) considered that there is a continuum between open and closed inflorescences in the genus. ...
The floral developmental patterns and carpel morphologies of Potamogeton illinoensis Morong, P. polygonus Cham. et Schltdl and P. pusillus L. were investigated under light (LM) and scanning electron microscopes (SEM) to identify potential characteristics for taxonomic studies. The initiation order of the floral organs was similar in all species; floral phyllotaxy was whorled, with dimerous perigonium and androecium and tetramerous gynoecium. It is suggested that this phyllotactic pattern was acquired by the loss of one organ per whorl, in comparison to the monocots Bauplan. While P. polygonus and P. pusillus showed similar carpel development, P. illinoensis developed its carpels in a unique way, due to a greater growth of the dorsal wall, which positions the carpel opening just above the ovule. Additionally, P. illinoensis may form an extragynoecial compitum. The stigma shape and both the position and shape of the carpel opening were useful to distinguish the three species, and are identified as potential taxonomical characteristics.
... G.V. Degtjareva, D.D. Sokoloff filamentous structure was found in place of a second flower, i.e., in a position where another flower could be expected (Fig. 9i), a phenomenon that sporadically occurs in various angiosperms ( Sokoloff et al. 2006;Lock et al. 2009). ...
Earlier interpretations of shoot morphology and flower position in Pinguicula are controversial, and data on flower development in Lentibulariaceae are scarce. We present scanning electron microscopy about the vegetative shoot, inflorescence and flower development in Pinguicula alpina and P. vulgaris. Analysis of original data and the available literature leads to the conclusion that the general pattern of shoot branching and inflorescence structure is uniform in all the Pinguicula species studied so far. The inflorescence is a sessile terminal umbel that is sometimes reduced to a solitary pseudoterminal flower. Flower-subtending bracts are either cryptic or present as tiny scales. A next order lateral shoot develops in the axil of the uppermost leaf, below the umbel. It is usually though not always homodromous, i.e., the direction of the phyllotaxy spiral is the same as in the main shoot. Among Pinguicula species that overwinter as a hibernaculum, the initiation of floral organs takes place in the same year as flowering in P. vulgaris, and 1 year earlier in P. alpina. Early congenital petal fusion (‘early’ sympetaly) is documented in Pinguicula, though most other members of Lamiales exhibit ‘late’ sympetaly. Sporadic occurrence of rudiments of two posterior stamens in Pinguicula is confirmed. A speculation is made that, in angiosperms, monosymmetric flowers cannot be terminal on shoots bearing more than two (or three) phyllomes.
... Terminal flower like structures have been also detected, with a higher or a lower frequency, when studying the natural variation in the inflorescence structure in natural populations of various monocot and dicot plants that normally have inflorescence lacking a terminal flower (Buzgo and Endress, 2000;Buzgo et al., 2004;Sokoloff et al., 2006;Lock et al., 2009). Analysis of the terminal flower like structures in plants and their comparison with the corresponding structures in mutants of model organisms are impor tant for understanding the mechanisms involved in the regulation of morphogenesis common for angio sperms as well as for detection of possible directions in evolutionary rearrangements of inflorescences and particular scenarios of such rearrangements (Sokoloff et al., 2006). ...
Flowers of Ruppia are usually arranged into an open two-flowered spike, but sometimes two lateral flowers are congenitally united with each
other forming a terminal flower-like structure. This deviation from the morphogenesis of reproductive structures typical of
Ruppia resembles those described in well-studied mutants of the model organisms of developmental genetics, such as Arabidopsis and Antirrhinum. A study of Ruppia allows the morphogenetic lability of this trait to be traced in natural populations. These data are important for understanding
the evolutionary transition from open to closed inflorescences. This paper describes the first data on the frequencies of
terminal flower-like structures in natural populations of Ruppia maritima as well as on the specific features of their morphogenesis. The vascular supply in the inflorescences with free and fused
flowers is also compared for the first time. It has been demonstrated that the frequency of inflorescences with fused flowers
considerably varies between different populations. The data on variation in the number of organs in flowers of plants from
different populations suggest that an increased size of floral primordia is a factor enhancing their fusion into a joint primordium
of the terminal structure. The vascular system of the R. maritima inflorescences with united flowers is similar to the vascular system of a single flower; moreover, nothing contradicts the
hypothesis on a terminal position of this structure. The R. maritima inflorescences with united flowers frequently contain transversal stamens with an inverted polarity. Presumably, this is
the first case of recorded inversion of relative polarity of stamens and carpels in angiosperms.
Keywordsmorphogenesis–inversion of polarity–congenital fusion–inflorescence–terminal flower-like structures–fasciation–flower–
Ruppia
