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Pollen diversity in Cyperaceae
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The pollen grain morphology of 30 species of 27 genera from the four subfamilies of the Cyperaceae have been studied with LM and SEM. Several methods were tested in order to find the optimal treatment for the delicate Cyperaceae pollen grains. For LM, treatment with wetting agent Agepon and KOH yielded the best results, while critical point drying (CPD) after fixation with alcohol proved to be the best method for studying pollen grains of Cyperaceae with SEM. Our results show that the Mapanioideae have a pollen grain type (only one distal ulcus) clearly different from the other Cyperaceae. Representatives of the examined Sclerioideae and Caricoideae show a similar pollen grain type (mostly one distal ulcus and three lateral pores) while in the Cyperoideae different pollen grain types are found.
Pollen character evolution in yams (Dioscorea: Dioscoreaceae) was investigated in relation to the phylogeny obtained from a recent combined analysis of rbcL and matK gene sequences. The following characters were evaluated: pollen size, aperture number, sexine ornamentation, perforation density, and orbicule presence or absence. Continuous characters were coded using the gap weighting method. Each character was optimized using MacClade onto a tree selected at random from analyses based on molecular data of Wilkin et al. The results indicate that in Dioscorea pollen size decreases in the more derived clades. The latter observation may be related to the evolution of annually replaced tubers. Aperture number increases from one in the monosulcate Stenophora clade (sister to the rest of Dioscorea) to two in other Dioscorea clades. This may be related to the presence of simultaneous microsporogenesis in Dioscorea. A perforate sexine is plesiomorphic in Dioscorea and a striate pattern has evolved more than once and is particularly characteristic in the Malagasy clade. Sexine ornamentation in the Stenophora clade is diverse. The endemic allotetraploid D. pyrenaica is characterized by large, monosulcate, gemmate pollen. The Dioscorea B clade is characterized by pollen with small, dense perforations. Orbicules occur in all Dioscorea species, but are absent in most of the outgroup taxa.
Quantitative data play an important role in palynological research. With the advent of digital imaging in light and electron microscopy, palynologists now have the opportunity to perform measurements faster and more precisely than ever before. Several image analysis software packages already exist for these tasks, but they are often expensive, difficult to use or not adapted to the specific needs of palynologists. After studying the daily workflow of a palynologist, we designed CARNOY, an image analysis application written from the ground up for use in palynology and morphology. CARNOY offers an easy-to-use interface and several features to make measuring easier and faster. The program can export measurements to almost every other software package for further analysis and is available for free on the Internet.
Pollen morphology of 20 species belonging to the 14 genera of the family Gramineae has been investigated using light microscope and scanning microscope. It is a stenopalynous in nature. Pollen grains mostly spheroidal, monoporate rarely diporate, ±circular, pores small operculate, non-operculate, annulate or non-annulate. Tectum areolate to scabrate. On the basis of exine ornamentations 5 distinct pollen types are recognized. Palynology do not correspond with tribal classification. However, palynology is significantl y helpful at the specific and generic level within the tribes.
The pollen of New Zealand Cyperaceae have not been previously identified below family level. However, a recent shift towards studying more ecological detail with greater temporal resolution in palynological research has now led to a demand for greater precision in pollen identification. In this paper we describe the pollen characteristics, mainly grain shape and aperture type, of representatives of each New Zealand Cyperaceae genus. Twelve distinct groups are defined, and a key is provided to assist with their identification, usually either to a genus or to a group of genera described as a particular type.
Descriptions of the 122 genera of Cyperaceae were automatically converted from a DELTA database to PAUP format and into distance matrices, for cladistic and phenetic analyses. Comments on the taxa included are provided, and an annotated and illustrated character list is presented. Subsets of characters and taxa were analysed and the results compared with previous classifications of the family, including one recently derived from manual cladistic analyses. The cladistic analyses were more successful in providing reasonable hypothetical phylogenies than in providing classifications permitting useful generalisation: The phenetically derived trees are in general similar to the cladograms, but they are more highly structured and correspond more closely to a previously published, manually derived cladogram. A suprageneric classification of the Cyperaceae is proposed, in which the genera are explicitly assigned to twelve tribes and two subfamilies. The interactive program INTKEY was used for preparing group descriptions and diagnoses, thus greatly facilitating comparisons among alternative classificatory solutions. Weaknesses of literature generalisations, particularly at higher taxonomic levels, highlight the need for more comparative data.
Although the majority of systematic palynologists use Erdtman's acetolysis method or the slightly modified method of Reitsma for the preparation of pollen grains for LM and SEM observations, these methods have some major drawbacks. Especially within monocots, pollen grains are often thin-walled, and therefore tend to collapse even after a mild acetolysis, as experienced, for instance, in Cyperaceae and Dioscoreaceae, among other groups. Very satisfying results Often are obtained by the use of fresh material. Unfortunately, this is not available in most cases, especially when working on tropical taxa-hence making herbarium material indispensable. We present a comparison between three major methods for the treatment of fragile pollen (KOR/CPD-treatment, glutaraldehyde/CPD-treatment, and a mild acetolysis) and introduce a new enzyme-based method using cellulase and pectinase. All four methods are tested on three different monocotyledons of three different orders: Allium ursinum L. (Liliales), Asparagus officinalis L. (Asparagales), and Tamus communis L. (Dioscoreales). The properties and results of each method are then critically assessed. The new method yields satisfying results especially on the hydration state and shape of the pollen grains.
Coding quantitative data has always been one of the most difficult steps in morphological phylogenetics. A robust and theoretically well-supported method for coding quantitative data was proposed by Thiele (1993). This method relies on differential weighting of gaps between coded states within one character. The downside of gap weighting is that it requires many calculations. In order to provide an easy way of integrating quantitative data into phylogenetic analyses, we have created MorphoCode, an open-source software project. MorphoCode implements a variation on Thiele's method and offers the user the possibility to import data as tab-separated text, to choose the number of character states and to export the newly coded data to a NEXUS file.
Since the Monocots II meeting in 1998, significant new data have been published that enhance our systematic knowledge of Cyperaceae. Phylogenetic studies in the family have also progressed steadily. For this study, a parsimony analysis was carried out using all rbcL sequences currently available for Cyperaceae, including data for two new genera. One of the four subfamilies (Caricoideae) and seven of the 14 tribes (Bisboeckelereae, Cariceae, Cryptangieae, Dulichieae, Eleocharideae, Sclerieae, Tri-lepideae) are monophyletic. Subfamily Mapanioideae and tribe Chrysitricheae are monophyletic if, as the evidence suggests, Hellmuthia is considered a member of Cypereae. Some other features of our analysis include: well-supported Trilepideae and Sclerieae–Bisboeckelereae clades; a possible close relationship between Cryptangieae and Schoeneae; polyphyletic tribes Schoeneae and Scirpeae; the occurrence of Cariceae within the Dulichieae–Scirpeae clade, and a strongly supported clade, repre-senting Cyperus and allied genera in Cypereae, sister to a poorly supported Ficinia–Hellmuthia– Isolepis–Scirpoides clade. Such patterns are consistent with other studies based on DNA sequence data. One outcome may be that only two subfamilies, Mapanioideae and Cyperoideae, are recognized. Much further work is needed, with efforts carefully coordinated among researchers. The work should focus on obtaining morphological and molecular data for all genera in the family.
Abstract— Data scored for cladistic analyses may be quantitative or qualitative, continuous or discrete, and show overlapping or non-overlapping values between taxa. Quantitative and qualitative are modes of expression of data, while continuous or discrete refer to properties of the set of numbers that express the data; both these pairs of terms have been confused with overlapping and non-overlapping. The degree of overlap of values between taxa is often used to filter characters in cladistic analyses: if a minimum amount of overlap is exceeded, or a minimum amount of disjunction not reached, characters are rejected as “not cladistic". However, this rests on a confusion between features of taxa and features of individual organisms (attributes). Cladistic characters are features of taxa, and comprise frequency distributions of attribute values over individuals of a taxon. Cladistic characters logically cannot overlap, although taxa may have overlapping attribute values. Thus, a priori rejection of characters that have overlapping attribute values is non-sensical. Such data may still be rejected from consideration for cladistic analysis if it could be demonstrated that they contain little recoverable phylogenetic signal. Few published analyses have empirically tested this. An analysis of overlapping morphometric data from three series of Banksia suggests that, at least in these cases, they map phylogeny almost as accurately as more conventional, qualitative morphological data. While more such tests are required, morphometric data should not be rejected a priori from cladistic analyses.
The phylogeny of suprageneric groups inCyperaceae has been examined by cladistic analysis ofrbcL sequence data of 80 species in 40 genera. The results support the family as monophyletic and derived from a juncaceous grade.Oxychloe (Juncaceae) has moderate support as the sister taxon toCyperaceae. Several monophyletic groups correspond to previously recognised tribes, and some similarities are noted between this analysis and previous cladistic analyses of primarily morphological data. Support is also given for the removal ofHellmuthia from tribeHypolytreae, the transfer ofIsolepis nodosa toFicinia, and the inclusion ofOxycaryum andKyllingiella in tribeCypereae. A polytomy comprisingCyperus, Juncellus, Kyllinga andPycreus indicates a broader circumscription ofCyperus. The greatest uncertainty lies with the generic and tribal status of theScirpeae.
In the last decade, efforts to reconstruct suprageneric phylogeny of the Cyperaceae have intensified. We present an analysis
of 262 taxa representing 93 genera in 15 tribes, sequenced for the plastid rbcL and trnL-F (intron and intergenic spacer). Cyperaceae are monophyletic and resolved into two clades, here recognised as Mapanioideae
and Cyperoideae, and the overall topology is similar to results from previous studies. Within Cyperoideae, Trilepideae are
sister to rest of taxa whereas Cryptangieae, Bisboeckelerieae and Sclerieae are resolved within Schoeneae. Cladium and Rhynchospora (and Pleurostachys) are resolved into clades sister to the rest of Schoeneae, lending support to the recognition of these taxa in separate tribes.
However, we retain these taxa in Schoeneae pending broader sampling of the group. The phylogenetic position of 40 species
in 21 genera is presented in this study for the first time, elucidating their position in Abildgaardieae (Trachystylis), Cryptangieae (Didymiandrum, Exochogyne), Cypereae (Androtrichum, Volkiella), Eleocharideae (Chillania), and Schoeneae (Calyptrocarya, Morelotia). More sampling effort (more taxa and the use of more rapidly evolving markers) is needed to resolve relationships in Fuireneae
and Schoeneae.
Orbicules, or Ubisch bodies, are sporopollenin particles lining the inner tangential and sometimes also the radial tapetal cell walls. They occur only in species with a secretory tapetum. The surface ornamentation of orbicules and pollen of the same species is often strikingly similar. Although orbicules were discovered more than a century ago, these structures remain enigmatic since their function is still obscure. Proposed hypotheses about their possible function are discussed. We also deal here with topics such as the possible allergenicity of orbicules and their representation in the fossil record. The use of orbicule characters for systematics is reviewed.
The distribution of orbicules throughout the angiosperms, based on a literature review from the first report until today, is shown in a list with 314 species from 72 families. Those species found in the literature without orbicules are presented together with their tapetum type. We plotted this information on a dahlgrenogram to visualize the distribution of orbicules. Orbicules occur in all subclasses of the angiosperms. Their occurrence is not correlated with certain modes of pollination or habitats.
In most flowering plants, a single cytokinesis follows the two meiotic divisions during pollen‐grain ontogeny. Aperture pattern (i.e., aperture number and distribution on pollen surface) ontogeny could be linked to the processes ensuring the apportionment of the cytoplasm to the four microspores.
This apportionment is achieved by radial arrays of microtubules organized around the nuclei. The cleavage planes are defined in the overlapping regions of opposing arrays extending from different nuclei. We followed the establishment of these arrays in two different lines of plants belonging to the genus Nicotiana that produce pollen grains with different aperture numbers. Different distributions of the microtubules have been observed, which can be interpreted as resulting from variation in the interactions between nuclei; these distributions appear to be correlated with aperture number.
As a consequence, we propose that simultaneous cytokinesis allows the formation of multiple pollen morphologies. This mechanism is consistent with aperture number distribution within angiosperms and provides clues to help our understanding of the evolution of aperture number.
Cyperaceae are the third largest monocotyledon family, with considerable economic and conservation importance. In subfamily Mapanioideae there is particular specialization of the inflorescence into units termed spicoids. The structural homology of the spicoid is difficult to interpret, making determination of intrafamilial relationships problematic. To address this, pollen from eight species in Mapanioideae was investigated using light microscopy and scanning and transmission electron microscopy. Pollen development was also examined to identify the type of pollen present in these species. We also analyzed DNA sequence data using the trnL-F and rps16 regions from 25 genera and 35 species of Cyperaceae, Juncaceae, and Thurniaceae. Two types of pollen, Mapania-type and pseudomonad, were identifed. Analysis of combined DNA and pollen data resolved a clade sister to the rest of Cyperaceae, corresponding to Mapanioideae. Within this, two further clades were resolved. One comprised taxa assigned to tribe Hypolytreae, which had Mapania-type pollen. The other comprised taxa mainly assigned to tribe Chrysitricheae, but included two taxa from Hypolytreae, Capitularina and Exocarya. All taxa in this clade had pseudomonad pollen. Thus new groupings within the subfamily have been discovered based on the specialization of some taxa in terms of their pollination biology.
Pariana, a primitive bamboo, is the only genus in the Gramineae (Poaceae) to have pollen grains without an annulus as part of its single aperture (porate) system. In contrast, the markedly thickened exine layer underlying the pore margin is similar to counterparts in all grass genera. Components of the future annulus in Gramineae pollen develop toward the cytoplasm (proximally) and begin to be pressed outward by an increase in the cytoplasm during the microspore vacuolate stage, culminating in an annulus by maturity. However, in some species of Pariana these components are either not sufficiently developed or the cytoplasmic expansion is not sufficient to press the components into an annular ring around the pore. The structural relationship of exine layering in this type of pollen grain in Gramineae and other families with similar apertures has not hitherto been extensively studied. A critical examination of the apertures in bambusoid grasses may clarify their systematic position within the Gramineae.
This paper critically reviews the distribution of microsporogenesis types in relation to recent concepts in monocot systematics.
Two basic types of microsporogenesis are generally recognized: successive and simultaneous, although intermediates occur.
These are characterized by differences in tetrad morphology, generally tetragonal or tetrahedral, although other forms occur,
particularly associated with successive division. Successive microsporogenesis is predominant in monocotyledons, although
the simultaneous type characterizes the ‘lower’ Asparagales. Simultaneous microsporogenesis also occurs inJaponolirion and Petrosavia (unplaced taxa), some Araceae, Aponogeton, Thalassia andTofieldia (Alismatales), Dioscorea, Stenomeris and Tacca (Dioscoreales), and some Commelinanae: Arecaceae (Arecales), and Cyperaceae, Juncaceae and Thurniaceae (Poales). Simultaneous
microsporogenesis is of phylogenetic significance within some of these groups, for example, Asparagales, Dioscoreales and
Poales. An intermediate type is recorded in Stemonaceae (Pandanales), Commelinaceae (Commelinales) and in Eriocaulaceae and
Flagellariaceae (Poales). There is little direct relationship between microsporogenesis type and pollen aperture type in monocots
(except for trichotomosulcate and pantoporate apertures), although trichotomosulcate apertures in monocot pollen, and equatorial
tricolpate and tricolporate apertures in eudicot pollen, are all related to simultaneous microsporogenesis. Copyright 1999 Annals of Botany Company
An anatomical survey of anthers of the Poaceae and Cyperaceae and two related families, the Restionaceae and Flagellariaceae, was conducted to determine the taxonomic distribution and possible phylogenetic significance of pollen arrangement. An unusual pollen arrangement was known from a small number of taxa in the Poaceae and Cyperaceae, in which a single, uniseriate cylinder of pollen grains is arranged in the anther locule such that each grain is in contact with the tapetum (termed here “peripheral” pollen). This contrasts with the prevailing arrangement in other angiosperms in which the locule contains a relatively large number of pollen grains in no special configuration, with many interior grains that never touch the tapetum (termed here “central” pollen). A total of 48 species in these four families was examined in this study, and observations on pollen arrangement for numerous additional species in these families were gleaned from the literature. We confirm that the peripheral arrangement is predominant in Poaceae and Cyperaceae, although both families also include species with central pollen, whereas only central pollen is found in Restionaceae and Flagellariaceae. In the peripheral arrangement, the pore of the pollen grain or pseudomonad, when observed, is in contact with the tapetum, but it has not been definitively demonstrated that this is always the case. Peripheral pollen in the Poaceae and Cyperaceae is nonhomologous because of the presence of pseudomonads in the latter family. It remains unexplained why peripherally arranged pollen or pseudomonads, with the attendant reduction in the number of pollen grains, should be associated with anemophily in these two families.
Herbaceous aquatic, semi-aquatic and marsh plants, some growing even in marine waters, which is unique in the angiosperms. The root hairs are developed from epidermal cells shorter that the ordinary epidermal cells (Leavitt 1904). Starch-rich rhizomes occur in several families but bulbs, corms and tubers are rare. Hibernacula occur in certain groups. The leaves are alternate or opposite. They may be uniformly linear and ribbon-like or differentiated into petiole and lamina. The veins in the former kind of leaf are parallel, those in the latter are arching and converging at the apex. Sparsely reticulate or transverse veins may occur. The leaf base is usually sheathing and invests the stem loosely. Stipules are present in various Zosterales and a few Alismatales (Hydrocharitaceae), and form the so-called “lingular sheaths” in the Potamogetonaceae. Intravaginal scales (or “squamules”) are almost diagnostic to the superorder (Arber 1923; von Staudermann 1924; Tomlinson 1982).
The pollen grain exine of Centrolepis aristata (R.Br.) Boem.& Schultz. is like a quilt with top and ("scrobiculii", Potonié 1934). Thus the top (tectum) extends down at intervals in the form of ringshaped extensions providing continuity with the footlayer. In effect there are no columellae (bacules). The ectexine system is alveolate and much like the cap region of pollen of Pinus. Prior to the microspore vacuolate period there is no continuous footlayer. Contents of the alveoli, which includes spherical bodies, are in direct contact with the cell surface. During vacuolate stages a footlayer is formed. At first it's structure includes spherical components. Before the vacuolate period there are no definite scrobiculi. As scrobiculi (and footlayer) develop After microspore mitosis an intine develops apparently beginning from the aperture region to the footlayer or across scrobiculi. Between footlayer and tectum, within the alveoli, there are spheres. Some spheres are in contact with the exine or even a part of it but most are without obvious contact with either tectum or footlayer. During the microspore vacuolate stage the tapetum degenerates. There is a massive influx of tapetal tapetal organelles and materials. The tectum of alveoli contact the cell surface before there is a footlayer. After formation of the footlayer it was in contact with the tectum. We refer to the zone proximal to the white-line lamellation of the junction plane in young material as a "transitory endexine".
The pollen cement („Pollenkitt“) originates in the tapetum inHeleocharis palustris. At first lipid drops appeare in the cells, then they conglomerate into groups, and ultimately form spindle-like bodies.
The electron microscope reveales a lamellar structure in these lipid bodies. Ultrathin sections show a finely striated pattern of light and dense lines. The center-to-center distance from one dense line to the next was found to be 88 Å. A single dense line is about 50 Å thick, consequently always thicker than a light one.
During the degeration of the tapetum the lipid bodies become free and enter into the antheresap. It becomes evident thereby that their nature is±elastic and not sticky.
The comparision ofHeleocharis with other plants shows that a relatively great quantity of cement substances does not necessary cause sticky insect-pollen — but may result in dry and powdery wind-pollen.
An anatomical survey of anthers of the Poaceae and Cyperaceae and two related families, the Restionaceae and Flagellariaceae, was conducted to determine the taxonomic distribution and possible phylogenetic significance of pollen arrangement. An unusual pollen arrangement was known from a small number of taxa in the Poaceae and Cyperaceae, in which a single, uniseriate cylinder of pollen grains is arranged in the anther locule such that each grain is in contact with the tapetum (termed here 'peripheral' pollen). This contrasts with the prevailing arrangement in other angiosperms in which the locule contains a relatively large number of pollen grains in no special configuration, with many interior grains that never touch the tapetum (termed here 'central' pollen). A total of 48 species in these four families was examined in this study, and observations on pollen arrangement for numerous additional species in these families were gleaned from the literature. We confirm that the peripheral arrangement is predominant in Poaceae and Cyperaceae, although both families also include species with central pollen, whereas only central pollen is found in Restionaceae and Flagellariaceae. In the peripheral arrangement, the pore of the pollen grain or pseudomonal, when observed, is in contact with the tapetum, but it has not been definitively demonstrated that this is always the case. Peripheral pollen in the Poaceae and Cyperaceae is nonhomologous because of the presence of pseudomonads in the latter family. It remains unexplained why peripherally arranged pollen or pseudomonads with the attendant reduction in the number of pollen grains, should be associated with anemophily in these two families.
Sixteen species of 14 genera of 7 different tribes of the Cinchonoideae (Rubiaceae) were investigated with a scanning electron microscope to examine orbicule presence and morphological diversity. Orbicules are lacking only in Gouldia terminalis (Hook, et Arn.) Hbd. and Simira rubescens (Benth.) Bremek. ex Steyerm. Four orbicule types could be distinguished mainly on the basis of shape and ornamentation characteristics. Spiny orbicules (type I) we found only in the Catesbaeeae (sensu Delprete). Augusta longifolia (Spreng.) Rehd. has microrugulate orbicules (type II). Smooth and spherical orbicules smaller than 0.5 μm (type III) are most widespread in our sample of the Cinchonoideae. In Burttdavya nyasica Hoyle, they are irregular and folded (type IV). For each species a description is given of the orbicule and of the sexine morphology, to allow comparison. Species with spiny orbicules always have microspines on the pollen sexine. For the other orbicule types no such resemblance could be observed. Transmission electron microscope observations of four species are included to comment on ultrastructural differences between orbicule types. From this preliminary survey, we suggest that orbicule features in Cinchonoideae may be systematically useful on generic and tribal levels. Key words: Ubisch bodies, Rubiaceae, Cinchonoideae, orbicule ultrastructure, tapetum.
Pollen morphological studies using LM and SEM have been carried out on six cultivars of Basmati – a variety of cultivated species Oryza sativa race Indica. SEM study at a magnification of ×20,000 revealed distinct variations in pollen exine surface patterns, in relation to the arrangements of fine surface excrescences (spinules or granules) and their clustering patterns forming small areas or insulae. Three distinctly different insular patterns occur in cultivars Basmati-370, Karnal local and Type-9. Cultivar Bakul Joha is characterized by free spinules. Mixed type i.e. both free and fused excrescences were observed in cultivars Bengali Joha and Bhog Maniki but they can be differentiated on the basis of the dimensions of the excrescences.
The pollen morphology of Butomaceae, Limnocharitaceae and Alismataceae, the three families comprising the Alismatales, was studied using light and scanning electron microscopy. Pollen grains of the monotypic Butomaceae are monosulcate and boat-shaped, those of Limnocharitaceae have 4-10 ill-defined, fimbriate, globally distributed pores, and those of most Alismataceae are pantoporate and spheroidal, or rounded polyhedral. However, Alisma oligococcum has unusual 2-porate, lens-shaped pollen grains, indicating an isolated position in the family so far as apertures are concerned. Pollen morphological characters of the order were analysed using cladistic methods and a hypothesis for pollen evolution in the Alismatales is presented. Monosulcate pollen is clearly primitive in the order, as amongst monocotyledons in general, whilst derived pollen grains possess higher numbers of pores. Fimbriate aperture margins, areas of circumporal ornamentation and sunken apertures are also considered derived. The general trend towards higher aperture numbers parallels aperture evolution amongst certain dicotyledons.
Related website, which covers Cyperaceae and many other families, is available via http://apps.kew.org/wcsp/prepareChecklist.do;jsessionid=7BCCAAD04EF2C551C17BE4D8C8F08360?checklist=selected_families%40%40047160220150936688 - see each database for authorship. NOTE: the original publication was only available in hardcopy (you may have to find a second-hand copy now) ; the website is kept updated so its content is more current.
PLEASE NOTE: THE AUTHORS HAVE NO COPIES TO GIVE AWAY.
The phylogeny of Cyperus and allied genera has been reconstructed using cladistic analysis of plastid rbcL gene, rps16 intron, trnL intron, and trnL-F intergenic spacer sequence data in 40 species of tribe Cypereae. Cyperus s.s. as currently circumscribed is not monophyletic because ten cyperoid genera are embedded within it. Eucyperoid Cyperus species (with a C3 anatomy, e.g. C. involucratus) and the genera Courtoisina, Kyllingiella and Oxycaryum form a clade that is sister to a clade comprising chlorocyperoid species (with a C4 anatomy, e.g. C. papyrus) and the genera Alinula, Ascolepis, Kyllinga, Lipocarpha, Pycreus, Remirea and Sphaerocyperus. The position of two species is uncertain; C. tenellus is resolved in a clade together with Isolepis although with typical cyperoid spikelets, whereas I. humillima is not resolved near either Isolepis or Cyperus s.l. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 138, 145–153.
During microsporogenesis sporopollenin becomes accumulated independently by the only two sporopollenin-producing cell types in the higher plants—the anther tapetum and the microspores—not only within the exine, but also within the orbicules. In Spermatophytes usually only a single orbicule type is found, but sometimes, e.g., inEuphorbia palustris, two different types exist within a single species. Very interestingly, most orbicules are strikingly similar in their structure, sculpture, shape and dimension to the respective ektexine: e.g., smooth sporopollenin globules are found near the totally smooth exines ofEupomatia laurina andPentaphragma sinense respectively, while inDelonix elata andEuphorbia palustris the orbicules often look like some incomplete tectum pieces. All these parallelisms can be attributed to the homologous and therefore highly similar genetic information to form sporopollenin in the sporogeneous tissue and the anther tapetum. The orbicules should be seen neither as sporopollenin storage, as sporopollenin transfer vehicle, nor as sporopollenin surplus.