The tapetum and systematics in monocotyledons

This paper critically reviews the homologies and distribution of tapetum types in monocotyledons, in relation to their systematics. Two main types of tapetum are widely recognised: secretory and plasmodial, although intermediate types occur, such as the “invasive” tapetum described inCanna. In secretory tapeta, a layer of cells remains intact around the anther locule, whereas in the plasmodial type a multinucleate tapetal plasmodium is formed in the anther locule by fusion of tapetal protoplasts. In invasive tapeta, the cell walls break down and tapetal protoplasts invade the locule without fusing to form a plasmodium. When examining tapetum type, it is often necessary to dissect several developmental stages of the anthers. Secretory and plasmodial tapeta are both widely distributed in monocotyledons and have probably evolved several times, although there may be some systematic significance within certain groups. Among early branching taxa,Acorus andTofieldia have secretory tapeta, whereas Araceae and Alismatales are uniformly plasmodial. The tapetum is most diverse within Commelinanae, with both secretory and plasmodial types, and some Zingiberales have an invasive tapetum. Lilianae (Dioscoreales, Liliales, and Asparagales) are almost uniformly secretory.     

Microsporogenesis in Monocotyledons

This paper critically reviews the distribution of microsporogenesistypes in relation to recent concepts in monocot systematics.Two basic types of microsporogenesis are generally recognized:successive and simultaneous, although intermediates occur. Theseare characterized by differences in tetrad morphology, generallytetragonal or tetrahedral, although other forms occur, particularlyassociated with successive division. Successive microsporogenesisis predominant in monocotyledons, although the simultaneoustype characterizes the ‘lower’ Asparagales. Simultaneousmicrosporogenesis 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 microsporogenesisis of phylogenetic significance within some of these groups,for example, Asparagales, Dioscoreales and Poales. An intermediatetype is recorded in Stemonaceae (Pandanales), Commelinaceae(Commelinales) and in Eriocaulaceae and Flagellariaceae (Poales).There is little direct relationship between microsporogenesistype and pollen aperture type in monocots (except for trichotomosulcateand pantoporate apertures), although trichotomosulcate aperturesin monocot pollen, and equatorial tricolpate and tricolporateapertures in eudicot pollen, are all related to simultaneousmicrosporogenesis. Copyright 1999 Annals of Botany Company Microsporogenesis, monocotyledons, pollen apertures, phylogeny, tetrads, simultaneous, successive, systematics.     

Molecular phylogeny of monocotyledons inferred from combined analysis of plastid<Emphasis Type="Italic"> matK</Emphasis> and<Emphasis Type="Italic"> rbcL</Emphasis> gene sequences

Using matK and rbcL sequences (3,269 bp in total) from 113 genera of 45 families, we conducted a combined analysis to contribute to the understanding of major evolutionary relationships in the monocotyledons. Trees resulting from the parsimony analysis are similar to those generated by earlier single or multiple gene analyses, but their strict consensus tree provides much better resolution of relationships among major clades. We find that Acorus (Acorales) is a sister group to the rest of the monocots, which receives 100% bootstrap support. A clade comprising Alismatales is diverged as the next branch, followed successively by Petrosaviaceae, the Dioscoreales–Pandanales clade, Liliales, Asparagales and commelinoids. All of these clades are strongly supported (with more than 90% bootstrap support). The sister-group relationship is also strongly supported between Alismatales and the remaining monocots (except for Acorus) (100%), between Petrosaviaceae and the remaining monocots (except for Acorus and Alismatales) (100%), between the clade comprising Dioscoreales and Pandanales and the clade comprising Liliales, Asparagales and commelinoids (87%), and between Liliales and the Asparagales–commelinoids clade (89%). Only the sister-group relationship between Asparagales and commelinoids is weakly supported (68%). Results also support the inclusion of Petrosaviaceae in its own order Petrosaviales, Nartheciaceae in Dioscoreales and Hanguanaceae in Commelinales.Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10265-003-0133-3     

Endosperm development in the Araceae (Alismatales) and evolution of developmental modes in monocots

The Araceae, a basal-most family of Alismatales that basally diverged subsequent to Acorales in monocot phylogeny, are known to have diverse modes of endosperm development: nuclear, helobial, and cellular. However, the occurrence of nuclear and helobial endosperm development has long been debated. Here, we report a (re-)investigation of endosperm development in Lysichiton, Orontium, and Symplocarpus of the Orontioideae (a basal Araceae), in which nuclear endosperm development was recorded more than 100 years ago. The results show that all three genera exhibit a cellular, rather than nuclear, endosperm development and suggest that the helobial endosperm development reported as an “unmistakable record” from Ariopsis is likely cellular. Thus the Araceae are very likely characterized by cellular endosperm development alone. An extensive comparison with other monocots in light of phylogenetic relationships demonstrates that a plesiomorphic cellular endosperm development is restricted to the three basal monocot orders Acorales, Alismatales, and Petrosaviales, in which evolutionary changes from cellular to nuclear endosperm development occurred twice as major events, once within Alismatales and once as a synapomorphy of the eight remaining monocot orders, including Dioscoreales, Liliales, Asparagales, and Poales, and that helobial endosperm development, which is known for many monocot families, evolved as homoplasy throughout the monocots.     

Recircumscription of the monocotyledonous family Petrosaviaceae to include Japonolirion

Most systematists have favored placing Petrosaviaceae close to the Triuridaceae (formerly positioned within Alismatidae) by focusing on the mycoheterotrophic habit and nearly free carpels of Petrosaviaceae. Others have favored a position near the melanthioid lilies, perhaps serving as a linking-family to the Triuridaceae. We discuss the results of recently published, independent, and combined DNA sequence analyses that indicate a strongly supported sister relationship betweenPetrosavia (Petrosaviaceae) andJaponolirion (Japonoliriaceae). Molecular data show no connection of these genera to the Alismatales (including Tofieldiaceae), the Melanthiaceae s. str., the Liliales, or the Triuridaceae (now in Pandanales), although there are morphological similarities to each of these groups. A relationship to the Pandanales has been indicated in some molecular analyses, but this is not supported by bootstrap/jackknife analyses or by most morphological characters. BothPetrosavia andJaponolirion are native to high-evelation habitats and have bracteate racemes, pedicellate flowers, six persistent tepals, septal nectaries, three nearly distinct carpels, simultaneous microsporogenesis, monosulcate pollen, and follicular fruits. Outside of the Alismatales, no other monocotyledons share this combination of features. We therefore suggest that the Petrosaviaceae be re-circumscribed to includeJaponolirion. If the family's isolated position among the monocot orders continues to be found in phylogenetic studies, then recognition of the already published order Petrosaviales would be appropriate.     

单子叶植物高级分类阶元系统演化: matK、rbcL和18S rDNA序列的证据

基于两个叶绿体基因（matK和rbcL）和一个核糖体基因（18S rDNA）的序列分析,对代表了基部被子植物和单子叶植物主要谱系分支的86科126属151种被子植物（单子叶植物58科86属101种）进行了系统演化关系分析。研究结果表明由胡椒目Piperales、樟目Laurales、木兰目Magnoliales和林仙目Canellales构成的真木兰类复合群是单子叶植物的姐妹群。单子叶植物的单系性在3个序列联合分析中得到98％的强烈自展支持。联合分析鉴定出9个单子叶植物主要谱系（广义泽泻目Alismatales、薯蓣目Dioscorcales、露兜树目Pandanales、天门冬目Asparagalcs、百合目Liliales、棕榈目Arecales、禾本目Poales、姜目Zingiberales、鸭跖草目Commelinales）和6个其他被子植物主要谱系（睡莲目Nymphaeales、真双子叶植物、木兰目、樟目、胡椒目、林仙目）。在单子叶植物内,菖蒲目Acorales（菖蒲属Acorus）是单子叶植物最早分化的一个谱系,广义泽泻目（包括天南星科Araceae和岩菖蒲科Toficldiaccae）紧随其后分化出来,二者依次和其余单子叶植物类群构成姐妹群关系。无叶莲科Petrosaviaceac紧随广义的泽泻目之后分化出来,无叶莲科和剩余的单子叶植物类群形成姐妹群关系,并得到了较高的支持率。继无叶莲科之后分化的类群形成两个大的分支：一支是由露兜树目和薯蓣目构成,二者形成姐妹群关系：另一支是由天门冬目、百合目和鸭跖草类复合群组成,三者之间的关系在单个序列分析和联合分析中不稳定,需要进一步扩大取样范围来确定。在鸭跖草类复合群分支内,鸭跖草目和姜目的姐妹群关系在3个序列联合分析和2个序列联合分析的严格一致树中均得到强烈的自展支持,获得的支持率均是100％。但是,对于棕榈目和禾本目在鸭跖草类中的系统位置以及它们和鸭跖草目-姜目之间的关系,有待进一步解决。值得注意的是,无叶莲科与其他单子叶植物类群（除菖蒲目和泽泻目外）的系统关系在本文中获得较高的自展支持率,薯蓣目和天门冬目的单系性在序列联合分析中都得到了较好的自展支持,而这些在以往的研究中通常支持率较低。鉴于菖蒲科和无叶莲科独特的系统演化位置,本文支持将其分别独立成菖蒲目和无叶莲目Petrosavialcs的分类学界定。     

Systematic root anatomy of Asparagales and other monocotyledons

Root anatomy of several taxa of Asparagales and some taxa formerly included in Asparagales is described in a systematic context together with a literature review. The presence of a dimorphic outer layer with long and short cells is widespread in monocotyledons, indicating that it originated early in the monocot lineage, but whereas this layer is rhizodermal in most monocotyledons, in Asparagales and Araceae it is usually hypodermal. There may be a correlation between the presence of a velamen or a persistent rhizodermis in many Asparagales and Araceae and the presence of a dimorphic hypodermal layer. Many other root anatomical characters, such as the presence of vascular bundles in the central pith and a multi-layered sclerenchymatous cylinder, are probably xeromorphic and developed convergently.     

A Phylogenetic Analysis of the Plastid matK Gene with Emphasis on Melanthiaceae sensu lato

Abstract: The presented mat K tree primarily agrees well with the previously presented rbc L tree and combined rbc L + atp B + 18SrDNA tree. According to the mat K tree, the monocotyledons are monophyletic with 100 % bootstrap support. Acorus diverges first from all other monocotyledons (90 % bootstrap support) in which two major clades are recognized: one (89 %) consisting of Alismatanae and Tofieldia (Nartheciaceae), and the other (< 50 %) comprising Lilianae, Commelinanae and Nartheciaceae other than Tofieldia. Within the latter major clade, Petrosavia and Japonolirion (Nartheciaceae) (82 %) diverge first from the remaining taxa (< 50 %) in which two clades are formed: one (81 %) consisting of Pandanales, Dioscoreales and Nartheciaceae-Narthecioideae, and the other (< 50 %) comprising Liliales, Asparagales and Commelinanae. In the former clade, Dioscoreales and Narthecioideae are grouped together (88 %). In the latter clade, Asparagales and Commelinanae are grouped together (< 50 %). Differences between the mat K and rbc L tree topologies appear in the positions of Tricyrtis (Calochortaceae) and Dracaenaceae. Differences between the mat K and combined rbc L + atp B + 18SrDNA tree topologies exist in the positions of the Petrosavia-Japonolirion pair (Nartheciaceae) and Pandanales. The stop codon position of the mat K gene appears to be highly variable among the monocotyledons, especially in the Liliales.     

Phylogenetic Inferences and the Evolution of Plastid DNA in Campynemataceae and the Mycoheterotrophic <Emphasis Type="Italic">Corsia dispar</Emphasis> D.L Jones &amp; B. Gray (Corsiaceae)

The phylogenetic positions of the families Campynemataceae and Corsiaceae within the order Liliales remains unclear. To date, molecular data from the plastid genome of Corsiaceae has been obtained exclusively from Arachnitis, for which alignment and phylogenetic inference has proved difficult. The extent of gene conservation among mycoheterotrophic species within Corsiaceae remains unknown. To clarify the phylogenetic position of Campynemataceae and Corsiaceae within Liliales, functional plastid-coding genes of species representing both families have been analyzed. Examination of two phylogenetic data sets of plastid genes employing parsimony, maximum-likelihood, and Bayesian inference methods strongly supported both families forming a basal clade to the remaining taxa of Liliales. The first data set consists of five functional plastid-encoded genes (matK, rps7, rps2, rps19, and rpl2) sequenced from Corsia dispar (Corsiaceae). The data set included 31 species representing all families within Liliales, as well as selected orders that are related closely to Liliales (10 outgroup species from Asparagales, Dioscoreales, and Pandanales). The second phylogenetic analysis was based on 75 plastid genes. This data set included 18 species from Liliales, representing major clades within the order, and 10 outgroup species from Asparagales, Dioscoreales, and Pandanales. In this latter data set, Campynemataceae was represented by 60 plastid-encoded genes sequenced from herbarium material of Campynema lineare. A large proportion of the plastid genome of C. dispar was also sequenced and compared to the plastid genomes of photosynthetic plants within Liliales and mycoheterotrophic plants within Asparagales to explore plastid genome reduction. The plastid genome of C. dispar is in the advanced stages of reduction, which signifies its high dependency on mycorrhizal fungi and is suggestive of a loss in photosynthetic ability. Functional plastid genes found in C. dispar may be applicable to other species in Corsiaceae, which will provide a basis for in-depth molecular analyses of interspecies relationships within the family, once molecular data from other members become available.     

Monocot relationships: an overview

In 10 years, the monocots have gone from being one of the least studied and most phylogenetically misunderstood groups of the angiosperms to one of the best characterized. Based on analyses of seven genes representing all three genomes, the following clades have high bootstrap support: Acorales (with the single genus Acorus) is sister to the rest of the monocots, followed successively by Alismatales (including Araceae and Tofieldiaceae), Petrosaviales, Dioscoreales/Pandanales, Liliales, Asparagales, and finally a polytomy of Arecales, Commelinales/Zingiberales, Dasypogonaceae, and Poales. Many of these results also have support from at least some morphological data, but some are unique to the trees created from DNA sequence data. Monocots have been shown in molecular clock studies to be at least 140 million years old, and all major clades and most families date to well before the end of the Cretaceous. More data are required to clarify the positions of the remaining unclearly placed orders, Asparagles, Liliales, and Arecales, as well as Dasypogonaceae. More sequences from the nuclear and mitochondrial genomes are also needed to complement those from the plastid genome, which is the most sampled and thus far most pattern-rich.     

Multiple developmental pathways leading to a single morph: monosulcate pollen (examples from the Asparagales)

BACKGROUND AND AIMS: Early developmental events in microsporogenesis are known to play a role in pollen morphology: variation in cytokinesis type, cell wall formation, tetrad shape and aperture polarity are responsible for pollen aperture patterning. Despite the existence of other morphologies, monosulcate pollen is one of the most common aperture types in monocots, and is also considered as the ancestral condition in this group. It is known to occur from either a successive or a simultaneous cytokinesis. In the present study, the developmental sequence of microsporogenesis is investigated in several species of Asparagales that produce such monosulcate pollen, representing most families of this important monocot clade. METHODS: The developmental pathway of microsporogenesis was investigated using light transmission and epifluorescence microscopy for all species studied. Confocal microscopy was used to confirm centripetal cell plate formation. KEY RESULTS: Microsporogenesis is diverse in Asparagales, and most variation is generally found between families. It is confirmed that the whole higher Asparagales clade has a very conserved microsporogenesis, with a successive cytokinesis and centrifugal cell plate formation. Centripetal cell wall formation is described in Tecophilaeaceae and Iridaceae, a feature that had so far only been reported for eudicots. CONCLUSIONS: Monosulcate pollen can be obtained from several developmental pathways, leading thus to homoplasy in the monosulcate character state. Monosulcate pollen should not therefore be considered as the ancestral state unless it is produced through the ancestral developmental pathway. The question about the ancestral developmental pathway leading to monosulcy remains open.     

Microsporogenesis and systematics of Aristolochiaceae

Within Aristolochiaceae, a secretory tapetum and orbicules are ubiquitous, but both simultaneous and successive types of microsporogenesis occur. Simultaneous cytokinesis is apparently plesiomorphic within the order Piperales, in which Aristolochiaceae are now placed. Successive microsporogenesis was found only in species of Aristolochia confined to a crown clade in the proposed phylogeny of this genus. In contrast to many other taxa, within Aristolochiaceae there is no strict relationship between microsporogenesis type and tetrad configuration, which is strongly influenced by spindle orientation, especially during meiosis II. There is also no direct correlation between microsporogenesis type and the aperture of mature pollen grains.     

Embryology of <Emphasis Type="Italic">Hemerocallis</Emphasis> L. and its systematic significance

The embryology of the genus Hemerocallis L. was studied to re-evaluate its current systematic position proposed by recent phylogenies based on molecular data. Using the improved carbol fuchsin–aniline blue staining method and conventional paraffin sectioning technique, we followed the development of anther and pollen grain, ovule and female gametophyte, and embryo and endosperm up to seed maturity. Our results showed that the (1) anther wall development is of the Monocot type, with a one cell-thick middle layer and a secretory tapetum, (2) microsporocytes cytokinesis is of the intermediate type, (3) microspore tetrads are tetragonal or decussate, (4) pollen grains are two-celled, (5) ovary is superior and trilocular, with axile placentas bearing two collateral ovules per locule, (6) ovules are anatropous, tenuinucellate, and bitegmic, with micropyle formed by the inner integument, (7) megaspore tetrads are linear, and only the chalazal one is functional, (8) embryo sac development is typically of Polygonum type, (9) embryogenesis is of Graminad type, and (10) endosperm development is of nuclear type. Overall, our study thus confirms that the embryological features of Hemerocallis support its exclusion from Liliaceae in Liliales, its inclusion in Asparagales, and its affinities with Asphodelaceae.     

琼榄小孢子发生、雄配子体发育及花粉粒形态

利用光学显微技术和电镜扫描技术研究了琼榄的小孢子发生、雄配子体发育和花粉粒形态以增加广义心翼果科的胚胎学和孢粉学资料。主要结果如下：（1）花药四孢囊;（2）花药壁四层,从外到内分别为表皮、具纤维性加厚的药室内壁、退化早的中层和细胞具2~4核的分泌型绒毡层;（3）小孢子母细胞胞质分裂同时型,形成四面体型排列的小孢子四分体;（4）成熟花粉粒为二细胞型;（5）花粉粒具3个隐形萌发孔,外壁为网状纹饰。琼榄与心翼果属的小孢子发生和雄配子体发育特征非常相似,稍有不同。琼榄的花粉粒形态特征与同属其它种基本相同。     

Contribution of pollen and tapetal characters to the systematics of Triuridaceae

 Pollen and tapetal characters in the mycoheterotrophic monocot family Triuridaceae are here compared with those of their putative relatives, including the lilioid order Pandanales (Pandanaceae, Cyclanthaceae, Velloziaceae and Stemonaceae), with which Triuridaceae have recently been associated following analyses of molecular data. Triuridaceae have small, inaperturate (functionally monoaperturate) pollen grains with the exine reduced to gemmae which have distinctive protruberances or spines. Microsporogenesis is of the successive type. Some genera have a plasmodial tapetum. Orbicules are absent. These characters are compatible with a relationship with Pandanaceae, but a relationship with Alismatales, as suggested by earlier authors, cannot be excluded. Received June 18, 2002; accepted July 22, 2002 Published online: November 22, 2002 Address of the authors: Carol A. Furness (e-mail: c.furness@rbgkew.org.uk), Paula J. Rudall and Alison Eastman, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK.     

Embryology and possible relationships of Petermannia cirrosa (Petermanniaceae)

Conran, J. G. 1988. Embryology and possible relationships of Petermannia cirrosa (Petermanniaceae). - Nord. J. Bot. 8: 13–17. Copenhagen. ISSN 0107–055X.
Micro- and megasporogenesis in Petermannia cirrosa is reported and the relationships of the Petermanniaceae are discussed. Microsporogenesis is successive; the endothecium is spirally thickened and the tapetum binucleate and amoeboid. The ovules are anatropous and crassinucellate. A primary parietal cell is formed and divides. Megasporogenesis is of the Polygonum type. On the basis of these and other characters, the Petermanniaceae show affinities with the remainder of the Dioscoreales, and also with the Geitonoplesiaceae (Asparagales) but remain somewhat isolated.     

Pollen ontogeny in Magnolia liliflora Desr.

Pollen ontogeny contributes significantly to the evolutionary analysis and the understanding of the reproductive biology of seed plants. Although much research on basal angiosperms is being carried out there are still many important features about which little is known in these taxa, such as the sporophytic structures related to pollen development and morphology. In this study, pollen development of Magnolia liliflora was analyzed by optical microscopy and transmission electron microscopy. The aim of this paper was to supply data that will help characterize basal angiosperms. Microsporogenesis is of the successive type, so that tetrads are decussate or isobilateral. The callosic walls form by the centripetal growth of furrows. The secretory tapetum develops orbicules, which start to form in the microspore tetrad stage. Pollen grains are shed at the bicellular stage. The exine wall has a granular infratectum. Ultrastructural changes observed in the cytoplasm of microspores and tapetal cells are related to the development of the pollen grain wall and orbicules. Centrifugal cell plates are more usual for the successive type of microsporogenesis. The presence of the successive type of microsporogenesis with callosic walls formed by the centripetal growth of furrows could reflect the fact that the successive type in Magnoliaceae is derived from the simultaneous type. The granular infratectum of the ectexine and the presence of orbicules could indicate that this species is one of the most evolved of the genus.     

百合科山韭小孢子发生及雄配子体发育

利用石蜡切片对葱属植物山韭(Allium senescens L.)的小孢子发生及雄配子体形成进行了研究.结果表明:山韭花药具4个药室,花药壁由表皮、药室内壁、中层和绒毡层4层细胞组成,属分泌型绒毡层.小孢子母细胞减数分裂的胞质分裂为连续型.成熟花粉为二胞型,偶见三胞型.在小孢子母细胞减数分裂和单核小孢子中出现许多异常行为,如染色体拖曳,落后染色体和后期桥,以及产生微核等,这可能是导致花粉败育的原因之一.     

Links between early pollen development and aperture pattern in monocots

Summary. Although the pollen grains produced in monocots are predominantly monosulcate (or monoporate), other aperture types are also found within this taxonomic group, such as the trichotomosulcate, inaperturate, zonaperturate, di-, or triaperturate types. The aperture pattern is determined during the young-tetrad stage of pollen development and it is known that some features of microsporogenesis can constrain the aperture type. For example, trichotomosulcate pollen is always associated with simultaneous cytokinesis, a condition considered as derived in the monocots. Our observations of the microsporogenesis pathway in a range of monocot species show that this pathway is surprisingly variable. Our results, however preliminary, reveal that variation in microsporogenesis concerns not only cytokinesis but also callose deposition among the microspores and shape of the tetrads. The role played by these features in aperture pattern determination is discussed. Correspondence and reprints: Laboratoire Ecologie, Systématique et Evolution, Université Paris-Sud, 91405 Orsay Cedex, France.