ENDOTHECIAL THICKENINGS IN ANTHERS OF PORATE MONOCOTYLEDONS

A survey of the presence of endothecial thickenings in 20 genera from 11 families of porate monocotyledons tested the long-standing hypothesis that porate anther dehiscence is correlated with the absence of thickenings. Although this hypothesis is widely repeated in texts, it has been supported by a limited, biased data base from studies of Ericaceae and Melastomataceae, two large families of dicotyledons. The results of our broad study of monocotyledons show that endothecial thickenings are present in most porate monocotyledons. Thickenings are absent in only two of the 11 porate families surveyed, Mayacaceae and Commelinaceae, both in the Commelinales. Thickenings are also absent in Xyris (Xyridaceae), a nonporate genus. These findings indicate that in monocotyledons porate anther dehiscence and the absence of thickenings are not as closely related as previously supposed.     

Flavonoid relationships between the commelinaceae and related families

The Commelinaceae have been related taxonomically by several authors with the Gramineae, Cyperaceae; Juncaceae; Eriocaulaceae, Restionaceae, Zingiberaceae and Bromeliaceae. The flavonoids of these families were compared and analysed by cladistic methods. The cladogram, obtained by the Wagner groundplan-divergence method and numerical techniques, shows four possible main lines of evolution, one with flavonols as the dominant compounds (Zingiberaceae). The second line is also with flavonols but with modifications of the basic molecule (Eriocaulaceae, Restioinaceae, Bromeliaceae); a third line, characterized by the presence of tricin (Commelinaceae, Gramineae and Cyperaceae) and the fourth line, lacks $\text{C-}\text{glycosyl-flavones}$, with a high production of variously substituted flavones (Juncaceae).     

Systematic significance of pollen arrangement in MICROSPORANGIA OF POACEAE AND Cyperaceaei REVIEW AND OBSERVATIONS ON REPRESENTATIVE TAX A

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.     

ENDOTHECIUM IN IRIDACEAE AND ITS SYSTEMATIC IMPLICATIONS

An examination of the endothecial thickenings in 44 species of Iridaceae, selected from the four subfamilies and all major tribes, provides useful information about generic and tribal relationships in the family. U-shaped thickenings occur in Nivenioideae and Iridoideae—Sisyrinchieae, the latter the least specialized tribe of its subfamily. The occurrence of helical thickenings in all members examined of Iridiodeae tribes Irideae, Mariceae, and Tigridieae (a putatively monophyletic group) and Ixioideae is consistent with the recognition of these two lines as distinct taxa based on anatomical, morphological, phytochemical, and in the case of Ixioideae, palynological criteria. Baseplate thickenings are restricted to Patersonia. However, the shrubby Cape genera—Nivenia, Klattia, and Witsenia—have U-shaped thickenings which show a tendency for the bars on the inner periclinal cell walls to anastomose, suggesting a trend towards the baseplate condition in Patersonia. This accords with a suggested relationship between these genera, based on anatomical and flavonoid similarities. The pattern of variation in endothecial thickenings in Iridaceae is consistent with the phylogeny proposed by Goldblatt (1990). The distribution of thickening types within the family does not make it possible to polarize this character, but the most parsimonious interpretation assumes that U-shapes are basic. However, in at least some other monocotyledonous families the pattern suggests that U-shaped thickenings are derived from helices.     

(1->3),(1->4)-{beta}-d-Glucans in the cell walls of the Poales (sensu lato): an immunogold labeling study using a monoclonal antibody

(1→3),(1→4)-?-Glucans had previously been detected in nonlignified cell wall preparations of only the Poaceae and five other families in the graminoid clade of the Poales (s.l.). Cell walls of vegetative organs of 12 species in nine families of the Poales (s.l.) were examined by immunogold labeling using a monoclonal antibody to (1→3),(1→4)-?-glucans. Three types of wall-labeling patterns were identified depending on the density of labeling of the nonlignified walls of epidermal and parenchyma cells and the lignified walls of sclerenchyma fibers and xylem tracheary elements: type 1 in Poaceae and Flagellariaceae, type 2 in Restionaceae and Xyridaceae, and type 3 in Cyperaceae and Juncaceae. Type 1 had the heaviest labeling of nonlignified walls and type 2 the heaviest labeling of lignified walls. Type 3 had the least wall labeling, with only very light labeling of nonlignified and lignified walls. No labeling was found over walls of Typhaceae, Sparganiaceae, or Bromeliaceae. The results are discussed in relation to Poales phylogeny.     

PATTERNS OF ENDOTHECIAL WALL THICKENINGS IN ARACEAE: SUBFAMILIES POTHOIDEAE AND MONSTEROIDEAE

A survey of the patterns of endothecial wall thickenings in 106 representative species from 20 genera in the Pothoideae and Monsteroideae was made using cleared anthers, sections and macerations. The wide variety of wall thickenings that is present is based on an annular-helical pattern. Variations in thickenings are related to differences in cell shape, cell orientation, intergradation between helical and annular patterns, pitch of helices, presence of branched thickenings, and various types of discontinuities in thickenings. Notable exceptions to the annular-helical pattern include Culcasia, which lacks a differentiated endothecial layer with thickenings, and Acorus, which has a peculiar stellate pattern that is unique in the family. No single pattern consistently characterizes either subfamily, although continuous helices are common in the Monsteroideae, and rare in the endothecium of Pothoideae (except Anadendrum). Monsteroideae frequently exhibit a series of slanted separate thickenings on anticlinal walls, which is absent from Pothoideae except in Heteropsis. The slanted pattern is considered a variation on a rectangular helix, involving discontinuities of thickenings on the periclinal walls. Some monsteroid genera show considerably more interspecific variation (Rhaphidophora) than others (Monstera). Endothecial thickenings constitute an anatomical character that is useful in the systematic study of Araceae; present results support other anatomical studies in identifying Culcasia and Acorus as highly divergent genera in the Pothoideae.     

A SYSTEMATIC STUDY OF ENDOTHECIAL THICKENINGS IN THE ORCHIDACEAE

Endothecial cell thickenings were examined in anther macerations of representative species from 210 genera of the Orchidaceae. Nearly all species examined possessed the characteristic thickened walls which, in several tested species, gave a positive reaction to phloroglucinol, indicating the presence of lignin. Four basic thickening types were identified; distribution of the types was found to be largely in agreement with previously recognized suprageneric groups. Type I thickenings are tightly packed channels of loops or helices and were found in the “neottioid” genera, the Apostasioideae, and putatively basal genera in the remaining subfamilies. Because of its occurrence in the Apostasioideae, which is believed to be the most basal subfamily, Type I is hypothesized to be the plesiomorphic thickening type for the remainder of the Orchidaceae. Type II thickenings appear as scattered loops and may be a synapomorphy for the Orchidoideae, as they were found in all genera sampled from the subfamily except Disperis. Type III thickenings are circular in appearance and were found in the Cypripedioideae and in some members of the Spiranthoideae and Epidendroideae. Type IV thickenings show little regular arrangement, appearing to be scattered bars, and were observed primarily in the Epidendroideae and also in some Spiranthoideae. Three subtypes were recognized in Type III and Type IV. Some genera, such as Triphora, Goodyera, and Elythranthera, had thickenings that appeared intermediate between the recognized types. In general, terrestrial genera were found to have regularly arranged, well-developed thickenings, while many epiphytic groups showed congested, irregular, thinner thickenings.     

The systematic significance of the endothecium in Begoniaceae

The endothecial thickening patterns in 173 species, representing the three genera of Begoniaceae, were investigated using cleared macerated anthers. Begoniaceae contain taxa with U-shaped thickenings, perforate base plates, entire base plates, tympanate base plates, anticlinal bars, and taxa that lack endothecial thickenings. The degree of correlation between these endothecial classes and accepted taxonomic boundaries varies: some classes are confined to a single taxonomic unit (e.g. absence of thickenings, non-perforate tympanate base plates) while others are present in several taxonomic units (e.g. U-shapes, perforate base plates). This study provides an improved understanding of the diversity of endothecial patterns in a large genus and indicates that in the Begoniaceae the endothecium is of moderate systematic value within and between closely related sections in Begonia and in Symbegonia . We conclude that the endothecium exhibits high levels of homoplasy between distantly related sections of Begonia . In addition, we show that in contrast to past observations of the endothecium in dicotyledons, apical anther dehiscence in the Begoniaceae is not correlated with a loss of endothecial thickening.     

Microsporogenesis is simultaneous in the early‐divergent grass Streptochaeta,but successive in the closest grass relative,Ecdeiocolea

Simultaneous microsporogenesis is described for the first time in a grass, Streptochaeta spicata Schrad., a tropical Brazilian species that belongs in the early‐divergent subfamily Anomochlooideae. Microsporogenesis is successive in all other Poaceae examined so far, and most other members of the order Poales, to which grasses belong. The only other reports of simultaneous microsporogenesis in Poales are in Rapateaceae and some members of the cyperid clade (Juncaceae, Cyperaceae, Prionium and Thurnia). Among the graminids, Ecdeiocolea (the putative closest relative to Poaceae) is successive, as are Joinvillea, Flagellaria and all other Poaceae, indicating that the simultaneous condition is autapomorphic in Streptochaeta, though Anomochloa has yet to be examined. Anther wall development in Streptochaeta is of the reduced type, as also in another early‐divergent grass Pharus, though most other Poales, including most grasses, have the monocot type. In Streptochaeta, as in Pharus, the endothecium lacks thickenings, unlike other grasses that have a persistent endothecium with thickenings. The centrifixed anthers and nonplumose stigmas of Streptochaeta suggest entomophily.     

Diversity of germination strategies and seed dormancy in herbaceous species of campo rupestre grasslands

The effects of fire on the vegetation vary across continents. However, in Neotropical fire‐prone grasslands, the relationship between fire and seed germination is still poorly understood, while their regeneration, especially after strong anthropogenic disturbance, is challenging for their conservation. In the present study, we assessed diversity of germination strategies in 15 dominant herbaceous species from Neotropical altitudinal grasslands (locally known as campos rupestres). We exposed seeds to several fire‐related treatments. We also compared germination between regularly and post‐fire fruiting species. Finally, we investigated the diversity of dormancy classes aiming at better understanding the biogeography and phylogeny of seed dormancy. Germination strategies varied among families. Velloziaceae and Xyridaceae produced non‐dormant, fast‐germinating seeds. Cyperaceae and Poaceae showed an extremely low or null germination due to a high proportion of unviable or embryo‐less seeds. The seeds of campo rupestre grasslands are fire resistant, but there is no evidence that fire triggers germination in this fire‐prone ecosystem. Although heat and charred wood did not promote germination, smoke enhanced germination in one grass species and decreased the mean germination time and improved synchrony in Xyridaceae and Velloziaceae. Fire had a positive effect on post‐fire regeneration by stimulating fruit set in some Cyperaceae and Poaceae species. These species produced faster germinating seeds with higher germination percentage and synchrony compared to regularly fruiting Cyperaceae and Poaceae species. This strategy of dispersion and regeneration seems to be an alternative to the production of seeds with germination triggered by fire. Physiological dormancy is reported for the first time in several clades of Neotropical plants. Our data help advance the knowledge on the role of fire in the regeneration of Neotropical grasslands.     

Floral ontogeny and vasculature in Xyridaceae,with particular reference to staminodes and stylar appendages

We provide a detailed comparative study of floral ontogeny and vasculature in Xyridaceae, including Xyris, Abolboda and Orectanthe. We evaluate these data in the context of a recent well-resolved phylogenetic analysis of Poales to compare floral structures within the xyrid clade (Xyridaceae and Eriocaulaceae). Xyrids are relatively diverse in both flower structure and anatomy; many species incorporate diverse and unusual floral structures such as staminodes and stylar appendages. Xyridaceae possess three generally epipetalous stamens in a single whorl; the “missing” stamen whorl is either entirely absent or transformed into staminodes. Fertile stamens each receive a single vascular bundle diverged from the median petal bundle. In Xyris, the stamen bundle diverges at the flower base, but it diverges at upper flower levels in both Abolboda and Orectanthe. In species of Abolboda that possess staminodes, staminode vasculature is closely associated with the lateral vasculature of each petal. Despite the likely sister-group relationship between Eriocaulaceae and Xyridaceae, our character optimization indicates that the stylar appendages that characterize some Xyridaceae (except Xyris and Achlyphila) are non-homologous with those of some Eriocaulaceae. On the other hand, it remains equivocal whether the loss of a fertile outer androecial whorl occurred more than once during the evolutionary history of the xyrid clade; this transition occurred either once followed by a reversal to fertile stamens in Eriocauloideae and staminodes in some Xyridaceae, or twice independently within both Xyridaceae and Eriocaulaceae.     

THE OCCURRENCE OF INTERCALARY AND UNINTERRUPTED MERISTEMS IN THE INTERNODES OF TROPICAL MONOCOTYLEDONS

The distribution of percent of dividing nuclei, parenchyma cell length, total cell number per internode, and total internode length were determined for successive internodes in the apex and growing vegetative internodes of 23 tropical species in 17 families of monocotyledons. Basal intercalary meristems (IM) were found in representatives of Commelinaceae, Cyperaceae, Flagellariaceae, Poaceae, Restionaceae, and Marantaceae. Uninterrupted meristems (UM) which are confined progressively to the upper region of the internode and are not isolated meristematic regions were found in the Costaceae, Dioscoreaceae, Philesiaceae, Smilacaceae, Agavaceae, Araceae, Arecaceae, Liliaceae, Pandanaceae, and Zingiberaceae. Both IM and UM were found in different species of Orchidaceae. The only morphological trait correlated with meristem type was presence of sheathing leaf bases in all species with IM. Both IM and UM are interpreted as extensions of the primary elongating meristem; the IM is disjunct, and the UM is continuous with it. The phytomer growth unit and the presence of internodal IM's cannot be applied generally to the monocotyledons.     

VESSELS IN JUNCALES: II. CENTROLEPIDACEAE AND RESTIONACEAE

The occurrence and specialization of vessels in 6 genera and 14 species of Centrolepidaceae and 25 and 72, respectively, of Restionaceae are described. Those in Anarthriaceae (1 and 3) and Ecdeiocoleaceae (1 and 1), newly separated from Restionaceae, were also examined. Vessels in Ecdeiocolea are highly specialized; those in Centrolepidaceae are relatively primitive. Vessels in Restionaceae and Anarthriaceae are intermediate. Vessels in Cyperaceae and Gramineae are compared with those in Juncales in a review of vessels in Glumiflorae. Thurniaceae has most primitive vessels on the average, Juncales has more primitive vessels in leaves and inflorescence axes than does Cyperales; the opposite is true for roots, rhizomes and stems. Vessels in Graminales on the average are much more specialized than those in Cyperales and Juncales.     

Parasenecio chenopodiifolius (Compositae–Senecioneae) is a Synotis and conspecific with S. otophylla based on evidence from morphology,cytology and ITS/ETS sequence data

Observations on living plants and herbarium specimens have convinced us that Synotis otophylla (Compositae–Senecioneae) from south Xizang (Tibet), China, must be merged with the Himalayan Parasenecio chenopodiifolius. However, is the plant a Synotis or a Parasenecio? We have examined floral micro‐morphological and cytological characters of P. chenopodiifolius, and performed molecular phylogenetic analyses based on ITS and ETS sequence data. The anther collar of this taxon is balusterform, and the endothecial tissue cell wall thickenings are radial. These conform to the floral micro‐characters of Synotis but differ from those of Parasenecio, which has subcylindrical anther collars, and polarized endothecial tissue cell wall thickenings. Chromosome counts indicate the taxon has 2n = 40, a number common in Synotis, whereas Parasenecio has 2n = 60. Our phylogenetic analyses based on ITS/ETS sequences also place P. chenopodiifolius in Synotis. We make the new combination S. chenopodiifolia and synonymize S. otophylla.     

MEGAGAMETOPHYTE AND NUCELLUS IN RESTIONACEAE AND FLAGELLARIACEAE

Restionaceae are characterized by Polygonum-type development, a well-developed hypostase, the presence of starch grains in the mature female gametophyte, and a thick nucellus that is uniseriate at the micropylar end. Flagellaria indica differs in these characters. In general, proliferation of antipodals occurs in South African taxa of Restionaceae but not in Australasian taxa. The presence of multiplied antipodals is the usual condition in the allied family Poaceae, but the sporadic occurrence of this character in Restionaceae cannot be used to support the view that the two families are sister groups.     

Gondwanan evolution of the grass alliance of families (Poales)

Phylogenetic interrelationships among all 18 families of Poales were assessed by cladistic analysis of chloroplast DNA rbcL and atpB sequences from 65 species. There are two well-supported main clades; the graminoid clade with Poaceae (grasses), Anarthriaceae, Centrolepidaceae, Ecdeiocoleaceae, Flagellariaceae, Joinvilleaceae, and Restionaceae; and the cyperoid clade with Cyperaceae, Juncaceae, and Thurniaceae. A sister group relationship between Poaceae and Ecdeiocoleaceae is identified with strong support. The sister group of this pair is Joinvilleaceae. These relationships help in elucidating the evolution of grasses and the grass spikelet. Dating of the tree was done by nonparametric rate smoothing of rbcL molecular evolution. Most Poales families date back to the Cretaceous >65 million years ago (mya). Dispersal-vicariance analysis indicates that the Poales originated in South America, the cyperoid clade in West Gondwana (South America or Africa), and the graminoid clade in East Gondwana (Australia). The Trans-Antarctic connection between South America and Australia, and its breakup about 35 mya, probably influenced the evolution of the Poales and the graminoid clade in particular, leading to vicariance between the continents, but the separation of Africa from the other Gondwanan areas, completed about 105 mya, is too old for such a relation.     

Phylogenetic relationships between Juncaceae and Cyperaceae: insights from rbcL sequence data

Among the commelinid monocots, phylogenetic relationships involving Juncaceae and Cyperaceae have been difficult to resolve because of parallel and convergent evolution of morphological features. Using comparative sequencing of the chloroplast gene rbcL, hypotheses of relationships between these two families were tested. Sequences from 13 taxa were obtained for this study and analyzed using parsimony with 15 previously published sequences. Results of this analysis suggest that two genera of Juncaceae, Oxychloë and Prionium, are not closely related to the other genera of this family. Further, Cyperaceae appear to be more closely related to Juncaceae than to Poaceae, with which Cyperaceae are sometimes classified. In fact, Cyperaceae appear to be derived from within Juncaceae. The progenitor-derivative relationship of Juncaceae and Cyperaceae suggested by this study reveals an additional example of paraphyletic families which presents a series of taxonomic dilemmas.     

The megagametophyte in Anarthria (Anarthriaceae,Poales) and its implications for the phylogeny of the Poales

The development and structure of the megagametophyte of Anarthria (Anarthriaceae), Aphclia, and Centrolepis (Centrolepidaceae) are described. Anarthriaceae has tenuinucellate ovules and the Polygonum type of megagametophyte development, both characters typical of the Poales. However, it lacks the anticlinally elongated nucellar epidermis and numerous large starch bodies observed in the megagametophyte of Centrolepidaceae, both characters also present in Restionaceae. This relatively generalized megagametophyte structure is consistent with data from the chloroplast genome, which suggest that Anarthriaceae are not as closely related to Restionaceae as previously assumed. New data from the megagametophyte are analyzed cladistically together with other available information on the poalean families. The results show that there are two possible positions for Anarthriaceae: either as sister to Poaceae. Joinvilleaceae, Restionaceae, Ecdeiocoleaceae, and Restionaceae, or as sister to only the latter three families. The new data also allow a critical reevaluation of the phylogenetic position of Centrolepidaceae, which is either basal to the poalean clade (based on microgametophyte data), or embedded in the Restionaceae (based on anther structure and megagametophyte data).     

Ovule,fruit and seed development in Abolboda (Xyridaceae,Poales): implications for taxonomy and phylogeny

Xyridaceae belongs to the xyrid clade of Poales, but the phylogenetic position of the xyrid families is only weakly supported. Xyridaceae is divided into two subfamilies and five genera, the relationships of which remain unclear. The development of the ovule, fruit and seed of Abolboda spp. was studied to identify characteristics of taxonomic and phylogenetic value. All of the studied species share anatropous, tenuinucellate and bitegmic ovules with a micropyle formed by the inner and outer integuments, megagametophyte development of the Polygonum type, seeds with a tanniferous hypostase, a helobial and starchy endosperm and an undifferentiated embryo, seed coat derived from both integuments with a tanniferous tegmen and a micropylar operculum, and fruits with a parenchymatous endocarp and mesocarp and a sclerenchymatous exocarp. Most of the ovule and seed characteristics described for Abolboda are also present in Xyris and may represent a pattern for the family. Abolboda is distinguished by the ovule type, endosperm formation and the number of layers in the seed coat, in agreement with its classification in Abolbodoideae. The following characteristics link Xyridaceae to Eriocaulaceae and Mayacaceae, supporting the xyrid clade: tenuinucellate, bitegmic ovules; seeds with a tanniferous hypostase, a starchy endosperm and an undifferentiated embryo; and a seed coat with a tanniferous tegmen. A micropylar operculum in the seeds of Abolboda is described for the first time here and may represent a synapomorphy for the xyrids. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 144–154.     

Restionaceae seedlings: Morphology,anatomy and systematic implications

Restionaceae differ from most monocot families in having both epigeal and hypogeal germination. The green cotyledons associated with epigeal germination have a central vascular strand as found in most epigeal monocotyledons. In some genera the cotyledon may have a hairpin‐like structure, also described for Anthericaceae. The cotyledon of the hypogeal seedlings is short, without green pigment and largely remains embedded in the seed coat. Hypogeal germination is correlated with large, woody, indehiscent, frequently myrmecochorous nuts, while epigeal germination is found in species with smaller indehiscent nutlets or seeds, dispersed in a variety of ways. The primitive condition is most likely epigeal germination. In hypogeal seedlings of some African and Australian taxa an epicotyledonary rhizome is found between the primary root and the first leaves. Seedlings of African Restionaceae frequently have elongated culm internodes, whereas in the Australian species studied, internodes are very short, resulting in a cluster of seedling leaves. The leaf blades, which in most species are only found on the seedlings, are very simple anatomically. However, they appear to be unifacial, similar to the leaf blades of Anarthria (Anarthriaceae). The anatomical specialisations in the blades mirror those recorded for the culm anatomy. These observations are consistent with the hypothesis that Centrolepidaceae may be neotonous Restionaceae. They also corroborate the morphology of the African Restionaceae, and the presently accepted phylogeny of the African genera of Restionaceae.