Pollinium development and number in the Orchidaceae

Development of anthers in three subfamilies of Orchidaceae was studied anatomically to examine homology hypotheses for pollinium number characters and to produce a model of pollinium development for the family. Serial sections of plastic-embedded embryonic inflorescences revealed that anther primordia were either flattened or ovoid; subsequent expansion of thecae and their inward (adaxial) reorientation (“rotation”), achieved by differential cell division and elongation in the connective, result in a mature anther with strongly introrse morphology and pollinia oriented side by side (juxtaposed). Strongly introrse anthers occur in at least some members of all subfamilies and are probably the basal state for the family. All anthers examined (from Orchidoideae, Spiranthoideae, and Epidendroideae) showed a single meristematic region, which would later give rise to pollen, per theca at earliest stages; septation of each of these regions resulted in four or eight pollinia per anther, while lack of septation in some members of the Epidendroideae gave two pollinia. In contrast, the two bipartite pollinia found in many Spiranthoideae and Orchidoideae were produced by adherence of the contents of two locules at a late ontogenetic stage, and should be recognized as a distinct character state. Eight pollinia result from partitioning by two longitudinal septa or a longitudinal and a transverse septum; these two morphologies may also represent separate character states.     

Phylogenetic relationships in Epidendroideae (Orchidaceae), one of the great flowering plant radiations: progressive specialization and diversification

Background and Aims The largest subfamily of orchids, Epidendroideae, represents one of the most significant diversifications among flowering plants in terms of pollination strategy, vegetative adaptation and number of species. Although many groups in the subfamily have been resolved, significant relationships in the tree remain unclear, limiting conclusions about diversification and creating uncertainty in the classification. This study brings together DNA sequences from nuclear, plastid and mitochrondrial genomes in order to clarify relationships, to test associations of key characters with diversification and to improve the classification.Methods Sequences from seven loci were concatenated in a supermatrix analysis for 312 genera representing most of epidendroid diversity. Maximum-likelihood and parsimony analyses were performed on this matrix and on subsets of the data to generate trees and to investigate the effect of missing values. Statistical character-associated diversification analyses were performed.Key Results Likelihood and parsimony analyses yielded highly resolved trees that are in strong agreement and show significant support for many key clades. Many previously proposed relationships among tribes and subtribes are supported, and some new relationships are revealed. Analyses of subsets of the data suggest that the relatively high number of missing data for the full analysis is not problematic. Diversification analyses show that epiphytism is most strongly associated with diversification among epidendroids, followed by expansion into the New World and anther characters that are involved with pollinator specificity, namely early anther inflexion, cellular pollinium stalks and the superposed pollinium arrangement.Conclusions All tested characters show significant association with speciation in Epidendroideae, suggesting that no single character accounts for the success of this group. Rather, it appears that a succession of key features appeared that have contributed to diversification, sometimes in parallel.     

兰科雄蕊发育多样性研究进展

兰科是被子植物中多样性最丰富的家族,其雄蕊形态和功能分化在亚科间变化明显,是该物种多样性形成及适应性传粉生物学的研究重点。基于现有研究资料,该文初步归纳了兰科雄蕊发育多样性的主要研究内容及现状,为野生兰花资源的保护与利用提供科学依据。结果如下:(1)可育雄蕊数目的减少和花粉愈合程度的增加在兰科分子系统树上呈明显的平行演化趋势。(2)兰科雄蕊数目的减少和功能分化与早期花器官发生中存在大量的滞后和缺失、次生融合与分裂现象等密切相关。(3)花药开裂时的4类散粉单元的花粉超微形态特征在亚科、族、亚族、属和种间差异明显。(4)兰科花药散粉单元可以为单花粉粒,也可以通过花药发育过程中源自绒毡层的三类黏性物质而聚合成不同的散粉单元,包括花粉鞘、弹性黏素和其他黏性物质。(5)花药发育揭示了兰亚科的花粉小块结构主要有三类(红门兰型、树兰型和过渡型),树兰亚科的不同数目(2、4、8)和形态(全缘、浅裂、深裂、孔裂)的花粉团是由于花药原基分化出的不育隔膜组织的数目、朝向和位置而形成的。(6)兰科花药发育中,花药室数目、花药壁发育类型、绒毡层细胞核数目、不育隔膜组织分化、胞质分裂类型、小孢子四分体排列形式、花粉细胞核数目等在亚科和属间差异明显。然而,由于种类繁多,现有研究资料难以为理解兰科雄蕊发育提供清晰的线索,包括雄蕊的发育模式、散粉单元的形成机制、花药发育的胚胎学特征等。因此,有必要重视兰科雄蕊发育研究,包括扩大取样范围和利用多学科技术方法和修订兰科花形态常用术语等。     

铁皮石斛花粉块结构及发育过程的解剖学特征研究北大核心CSCD

兰科植物的有性生殖特殊,每朵花只有1个花药,且花粉有聚集成块发育的特征。为了揭示铁皮石斛花粉块的发育特征,该研究以野生铁皮石斛不同时期的花药为材料,采用半薄切片和植物组织化学方法对其发育过程进行解剖学观察分析,并对成熟花粉块进行离体培养,观察花粉管的萌发状况。结果表明:(1)铁皮石斛花药壁由1层表皮细胞,2层药室内壁细胞,1层中层细胞和1层绒毡层细胞组成。开花时,绒毡层细胞退化,中层细胞没有退化,药室内壁细胞则形成纤维状细胞壁;药室中的小孢子母细胞没有明显的胼胝质壁结构。(2)小孢子发生属同时型,减数分裂后四分体小孢子不分散,以四合花粉状态发育,并进一步连接形成花粉块。(3)在小孢子发育中,孢粉素覆盖在整个花粉块表面形成花粉外壁,但花粉块内部的花粉没有花粉外壁结构;在花粉块表面的花粉外壁上未见花粉萌发孔。(4)在花粉离体萌发实验中,具有花粉外壁的花粉块表面花粉未见萌发,仅由花粉块内部的花粉萌发出花粉管。     

兰科新种巾唇兰的花粉团发育及分类学意义

巾唇兰属是我国新记录属,近十余年来先后在我国南方发现了两种,包括在云南发现的新种——巾唇兰（Pennilabium yunnanense）。利用解剖镜和石蜡切片技术观察了巾唇兰具有分类学意义的花形态特征和花粉团发育的胚胎学特征,结果如下。成熟花的合蕊柱短,无蕊柱足;花粉块由2个球形花粉团、粘盘和粘盘柄组成。在花药发育早期,花药原基分化出一对侧生并列药室;在小孢子母细胞时期,每个小孢子囊在两个药室相邻的内花药壁处分化出一段不贯穿药室的不育隔膜组织。在花药发育过程中,该隔膜组织逐渐被吸收降解,到花粉成熟时形成2个开口朝内的孔裂花粉团。发育成熟的花药壁共有4层,发育类型为单子叶型,绒毡层为单核、腺质型。在小孢子母细胞进入减数分裂阶段,表皮细胞变窄出现了降解,中层和绒毡层细胞也逐渐被吸收和降解;花药成熟时,花药壁仅剩下残缺的表皮和纤维状加厚明显的药室内壁。小孢子母细胞通过同时型胞质减数分裂形成小孢子四分体,其排列方式主要为正四面体形和左右对称,成熟花粉为2细胞型。本文从形态发育角度澄清了巾唇兰花粉团特征的描述,讨论了其花粉团发育特征的分类学意义,为兰科花药发育多样性提供了新资料。     

Gynostemium micromorphology and pollination in Epipactis microphylla (Orchidaceae)

Self-pollination conditions have been recorded frequently in local populations of the genus Epipactis, and structural modifications have sometimes been reported, supporting taxonomic recognition of new species. As part of a survey of gynostemium micromorphology of Italian Epipactis populations, we studied an Apennine population of Epipactis microphylla (Ehrh.) Sw. a species listed as autogamous but with residual allogamous characters. In this population we observed the tendency to perform pre-anthesis cleistogamy. However, self-pollination was not a consequence of modification in column morphology. Cryptic pollen germination occurred in anther thecae or in the clinandrium, bypassing any contact with the receptive stigma. Pollen germination started from the distal pool of the pollinium, close to the rostellum-viscidium, suggesting that the rostellum-viscidium may have a function in promoting pollen-tube growth. Germinated pollen was exposed at the anthesis.     

The floral morphology and ontogeny of some Chinese representatives of orchid subtribe Orchidinae

The flower structure and development of ten species in six genera of the orchid subtribe Orchidinae are described and illustrated by scanning electron micrographs. Particular attention is given to the structure of the gynostemium, which for most species is interpreted from ontogenetic data. All the species studied here share a series of features, e.g. the sequence of tepal and anther initiation, the shape and position of the anther, the presence of auricles and basal bulges, the three-lobed condition of the median carpel apex and the lateral lobes of the median carpel embracing the basal ends of the thecae. However, the form and structure of the three carpel apices are most varied in the later development stages or in the adult flower. The genus Hemipilia shows a series of peculiar characters that are quite different from those of the other genera in Orchidinae. The peculiar structure and development of the viscidia in both Amitostigma and Neottianthe indicate that both of them are different from other genera in Orchidinae. The adult floral morphology shows that the genera Galearis and Chusua are not congeneric with Orchis. The separation of the lateral lobes of the rostellum in most genera studied here as well as in the Brachycorythis group from South Africa suggests that this is the ancestral state in the subtribe Orchidinae. In contrast, the conjoining of lateral lobes in Dactylorhiza and Orchis is suggested as a derived character.     

Pollen and anther ontogeny in Cabomba caroliniana (Cabombaceae, Nymphaeales)

Cabomba is a small water lily genus that is native to the New World. Studies of pollen development and associated changes in the anther yield valuable characters for considering the evolution of reproductive biology in seed plants. Here we characterized the complete ontogenetic sequence for pollen in Cabomba caroliniana. Anthers at the microspore mother cell, tetrad, free microspore, and mature pollen grain stages were studied using scanning electron, transmission electron, and light microscopy. Tetragonal and decussate tetrads both occur in C. caroliniana, indicating successive microsporogenesis. The exine is tectate-columellate, and the infratectal columellae are the first exine elements to form, followed by a continuous tectum and a thin foot layer. A lamellate endexine initiates in the early free microspore stage, but becomes compressed in mature grains. Tectal microchannels and sculptural rods also initiate during the early free microspore stage, and significant pollenkitt deposition follows, supporting the hypothesis that these elements function in entomophily. The tapetum is morphologically amoeboid, with migratory tapetal cells directly contacting developing free microspores within the anther locule. Results from this study illustrate the importance of including ontogenetic data in analyzing pollen characters and in developing evolutionary and ecological hypotheses. The new palynological data also emphasize the character plasticity that occurs in basal angiosperms.     

What does morphology tell us about orchid relationships?—a cladistic analysis

A cladistic analysis of Orchidaceae was undertaken for 98 genera using 71 morphological apomorphies based on a reconsideration of previous character analyses and newly discovered variation. The equally weighted analysis found 60 000 most parsimonious trees with low consistency (CI = 0.29) but high retention (RI = 0.83). The strict consensus reveals a significant amount of structure, and most traditionally recognized subfamilies are supported as monophyletic, including the Apostasioideae, Cypripedioideae, Spiranthoideae, and Epidendroideae. Orchidoideae in the broad sense are paraphyletic, giving rise to spiranthoids. Vanilloids are sister to epidendroids, although exhibiting several states otherwise found only in clearly basal groups, such as Apostasioideae. The nonvandoid epidendroids are poorly resolved, due to a high degree of homoplasy. The vandoids appear to be monophyletic, contrary to recent molecular evidence, possibly due to repeated parallel development of the vandoid character suite. The importance of vegetative characters as evidence putatively independent from floral features is demonstrated in the placement of Tropidia. Implied weighting analysis of these data resulted in similar patterns at high levels, although the Orchidoideae and Spiranthoideae may each be monophyletic and the nonvandoid epidendroids are more resolved. The high degree of structure implied in previous orchid classifications must be reconsidered, given the poor resolution at lower levels in the present trees.     

中国特有种苦绳(广义夹竹桃科)的大小孢子发生和雌雄配子体发育及其分类学意义

近年来的分子系统学把狭义萝藦科和狭义夹竹桃科合并为广义夹竹桃科,包括5个亚科和25个族,但亚科和族间的亲缘关系较为复杂,亟待多学科证据澄清。本文利用常规石蜡切片技术观察了马利筋亚科南山藤属中的中国特有植物苦绳(Dregea sinensis var. sinensis)的孢子发生和配子体发育,结合已有资料比较了5个亚科的胚胎学特征。结果表明:(1)苦绳的花药由一对侧生并列药室组成,各有一个花粉团。(2)花药壁有6层,由外至内分别为表皮、2层药室内壁、中层和2层绒毡层,花药壁发育模式属于多层型。(3)绒毡层细胞单核,排成2列,为腺质型; 在小孢子四分体形成时期,药室内壁发生明显纤维状加厚; 花药成熟时,位于药室远轴最外侧处的花药壁发生断裂,准备散粉。(4)小孢子母细胞减数分裂中,胞质分裂方式为连续型,小孢子四分体排列方式为左右对称; 成熟花粉粒为3-细胞型,排列紧密,形成花粉团。(5)雌蕊含有两枚离生心皮,具边缘胎座,胚珠倒生,单珠被,薄珠心,蓼型胚囊。本文观察到的这些胚胎学特征为牛奶菜族提供了新资料。同时,胚胎学特征在5个亚科间的区别和联系,支持广义夹竹桃科的成立。     

Evolutionary patterns in the terebratulid genus Caryona Cooper (Brachiopoda,Jurassic of France)

The study of ontogenetic and morphological changes in different species of the brachiopod genus Caryona COOPER (Terebratulidae) from the Lower Callovian‐Lower Oxfordian of northern France shows a succession (and an interference) of processes which vary according to the characters studied. This is an example of “mosaic evolution”;. The ontogenetic changes result from heterochrony, especially acceleration and hypermorphism. The main phylogenetic tendency is peramorphosis in most characters. This evolutionary pattern agrees with phyletic gradualism.

Moreover, analysis of the internal characters demonstrates the limited value of these in discrimination of the various genera.     

The tribal position of Fockea and Cibirhiza (Apocynaceae: Asclepiadoideae): evidence from pollinium structure and cpDNA sequence data

The pollinium morphology of the two members of the Asclepiadoideae, tribe Fockeeae, Fockea Endl. and Cibirhiza Bruyns, has been studied in detail and compared with that of eight genera of Marsdenieae, the tribe in which Fockea and Cibirhiza were previously accommodated and thus their putative closest relatives, as well as nine genera of Asclepiadeae. Both Fockea and Cibirhiza have several morphological characteristics in common, the most important of which is the absence of well-developed caudicula, which distinguishes them from all other genera of Asclepiadoideae known. The pollinium structure of these two genera, however, differs significantly. Whereas the pollinium of Cibirhiza consists of single pollen grains and is covered by a pollinium wall, as is typical for other Asclepiadoideae, the pollinium of Fockea consists of tetrads and is not covered by a pollinium wall, a condition otherwise typical of Secamonoideae. Fockea, however, has only two pollinia per anther, as does Cibirhiza and all other Asclepiadoideae, whereas the Secamonoideae have four pollinia per anther. Sequence data from two intergenic spacers, trnT-L and trnL-F and the trnL intron of cpDNA was analyzed. The ingroup included three species of Fockea and one species of Cibirhiza. The outgroup taxa consisted of three representatives each of Periplocoideae, and Secamonoideae and 24 species of Asclepiadoideae, including representatives of all tribes, of which eight genera belong to Marsdenieae, as outgroups. The results of the DNA analysis provide strong support for Fockeeae as a monophyletic tribe, distinct from Marsdenieae and, to the rest of the Asclepiadoideae. With the exception of pollen data, all morphological and molecular evidence clearly support recognition of the tribe Fockeeae. The occurrence of two such significantly different types of pollinia structure – characters elsewhere in the family used to distinguish subfamilies – within the small tribe Fockeeae was unexpected, and can perhaps best be understood as yet another attestment to the basal position of the Fockeeae in the nascence of the Asclepiadoideae.     

金线莲花药发育中的钙离子分布特征

该研究以金线莲不同发育时期的花药为材料,采用电子显微镜观察花粉块中的钙离子分布,以揭示钙离子在金线莲花药发育中的相关生理功能。结果发现:(1)在造孢细胞时期,较多的钙沉淀颗粒出现在花药表皮和药室内壁细胞的液泡中,暗示钙离子与植物细胞的液泡发生和形成有关。(2)在减数分裂前期,小孢子母细胞核中聚集了较多的钙沉淀颗粒,当小孢子母细胞分裂时,在二组染色体之间有大量的钙沉淀颗粒,显示钙离子与细胞分裂有关。(3)在合成淀粉的质体表面覆盖了较多的钙沉淀颗粒,显示钙离子与质体中的糖代谢有关。研究表明,开花时在花粉块表面的花粉外壁上和成熟花粉中仍保持有大量的钙沉淀颗粒,为花粉萌发所需钙离子做好了储备。     

Anther Wall of Cymbidium Goeringii with Special Reference to the Tapetum

The structure of the anther wall in Cymhidum goeringii (Rchb. f.)Rchb.f, was followed through two developmental stages using light and electron microscope: The peculiar anatomical pattern of the anther wall and the cytological characteristics of its tissues are described. Tapetum is the most notable feature in the anther wall. The specialized characteristics of the tapetal cells may be summerized as followings: (1) The tapetum may be distinguished into outer and inner tapetum, but they constitute the continuous layers surrounding the pollinium. The inner tapetum is derived from the connective tissue. (2) The outer and inner tapetum are composed of 2--3 cell layers. They have the same ultrastructural features and functions. (3) There are many lipid-containg plastids in the tapetal cells during their developmental stage. This is the main source of lipid bodies in the tapetal cells during their final developmental stage. The lipid-containing plasmids are derived from the extension of the nuclear membrane. (4) After the formation of tetrads, the secretion and the autolysates from of the tapetal cells not only deposition the surface of the pollinium to form the film, but also flow into the inner region of the polinia between the retrads contributing to their adhesion. The results of this study provide some new data of the tapetal structure and function in the angiosperms.     

Development of distylous flowers and investment of biomass in male and female function in Palicourea padifolia (Rubiaceae)

Knowledge of developmental pathways for achieving differences in style and anther heights, in concert with those of ancillary features accompanied with data in regard to biomass investment to male and female function, provide an excellent opportunity for examining the developmental correlations between primary and ancillary floral traits so as to understand the evolution of heterostyly. The ontogenetic relationships between bud length and anther height and between bud length and style height, and between bud length versus bud width, anther length, and number of pollen grains per anther for long-styled (LS) and short-styled (SS) morphs of P. PADIFOLIA are described. We also described the ontogenetic biomass allocation to male and female function and to corolla with elongation of buds harvested at regular intervals. We observed an early termination of stylar growth in SS buds, whereas LS styles steadily increased in size. Morph differences for relative growth rates were significant for anther height, anther length, and pollen number but not for bud width. Bud width and anther length had a negative allometric relationship with bud elongation. The relationship between bud length and number of pollen grains per anther was positive and morph differences in pollen number were detected at later stages of development. An increase in corolla mass involved a disproportionate allocation to the female function in SS flowers and male allocation was similar for the two morphs over the course of development. Our results are consistent with theoretical and empirical data for distylous species with an approach herkogamous ancestor, and with the more general hypothesis of ontogenetic lability of heterostyly, in which morph differences in style and anther heights are achieved in various ways. Variations observed in sexual investment between floral morphs suggest differences in sex expression during flower development.     

High-dimensional coexistence of temperate tree species: functional traits, demographic rates, life-history stages, and their physical context

Theoretical models indicate that trade-offs between growth and survival strategies of tree species can lead to coexistence across life history stages (ontogeny) and physical conditions experienced by individuals. There exist predicted physiological mechanisms regulating these trade-offs, such as an investment in leaf characters that may increase survival in stressful environments at the expense of investment in bole or root growth. Confirming these mechanisms, however, requires that potential environmental, ontogenetic, and trait influences are analyzed together. Here, we infer growth and mortality of tree species given size, site, and light characteristics from forest inventory data from Wisconsin to test hypotheses about growth-survival trade-offs given species functional trait values under different ontogenetic and environmental states. A series of regression analyses including traits and rates their interactions with environmental and ontogenetic stages supported the relationships between traits and vital rates expected from the expectations from tree physiology. A combined model including interactions between all variables indicated that relationships between demographic rates and functional traits supports growth-survival trade-offs and their differences across species in high-dimensional niche space. The combined model explained 65% of the variation in tree growth and supports a concept of community coexistence similar to Hutchinson's n-dimensional hypervolume and not a low-dimensional niche model or neutral model.     

Maeandrograptus schmalenseei and its bearing on the origin of the diplograptids

The earliest diplograptids were apparently monophyletic and are characterized by a streptoblastic development and strongly overlapping, markedly sigmoidal thecae. They may be grouped as the genus Undulograptus Bou¯ek 1973. The biramous, reclined Maeandrograprus schmalenseei Moberg 1892 of the upper Arenig Didymograptus hirundo Zone has a striking and detailed resemblance to these early diplograptids in the form of its proximal thecae, the style and degree of prothecal folding, and in the symmetry, form and orientation of the sicula and early thecae. Its appearance coincides with or slightly predates the appearance of diplograptids in the D. hirundo Zone. It is proposed as a representative of the group of biramous graptolites which were directly ancestral to the diplograptids. Derivation of the diplograptids from such a source would have involved some changes in the proximal thecal development, in the attitude of stipes and also in the form of the distal thecae - evolutionary changes which are known to have occurred in other graptolite groups.     

Adulthood and phylogenetic analysis in gastropods: character recognition and coding in shells of Lavigeria (Cerithioidea, Thiaridae) from Lake Tanganyika

In the study of gastropod shell morphology, determination of comparable ontogenetic stages is crucial, because all the states that various shell features go through during ontogeny are preserved on the shell. The protoconch/teleoconch transition and marks of episodic growth are among the few ways of defining discrete, comparable, growth stages. In gastropods with determinate growth the attainment of adulthood may provide additional shell markers permitting comparison among individuals and taxa. Adulthood is reflected in shell morphology in ways as diverse as shell deposition covering all the previous whorls and radically changing the shape of the shell through to slight changes in the trajectory of the suture. While the very prominent adulthood‐related changes of shell morphology have been used as systematic characters, the more moderate changes have not been studied in detail and their potential systematic value has been ignored. In this paper we give a detailed account of adult modifications of the shell appearing with cessation of growth. Our study group comprises eight closely related species of Lavigeria from Lake Tanganyika. We show that the ways adulthood is manifested are quite diverse. We describe eight characters of the aperture, the suture and the sculptural ornamentation. Character occurrence varies greatly among species. We show that characters appear in suites and that in many cases their appearance is connected to size. We use size as a proxy for adulthood and test whether character occurrence alone or its connection to size can help resolve species relationships. In both cases our characters confirm the monophyly of our ingroup and yield cladograms with various degrees of resolution of ingroup relationships. The coding method that yields the greater character congruence is the one that takes into consideration the connection between appearance of a character and size. This study demonstrates that ontogenetically correlated character transformations may nevertheless be phylogenetically independent. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 223?240.     

The structure and function of orchid pollinaria

Cohesive masses of pollen known as pollinia have evolved independently in two plant families — Orchidaceae and Asclepiadaceae. Yet, the bilateral symmetry of orchids has allowed a greater degree of specialization in pollination systems and a much greater diversity in the morphology of pollinaria — units comprising the pollinia(um) together with accessory structures for attachment to the pollinator. Pollinaria differ in the degree of cohesion of pollen in the pollinium, which may be soft, sectile (comprised of sub-units known as massulae) or hard. A single hard pollinium may contain more than a million pollen grains, yet pollen:ovule ratios in orchids are several orders of magnitude lower than in plants with powdery pollen due to the lack of wastage during transport to the stigma. Attachment of pollinia to the pollinator is usually achieved by means of a viscidium that adheres most effectively to smooth surfaces, such as the eyes and mouthparts of insects and beaks of birds. The stalk connecting a pollinium to the viscidium may be comprised of a caudicle (sporogenous in origin) and/or a stipe (derived from vegetative tissue), or be lacking altogether. Caudicles and stipes may undergo a gradual bending movement 20 s to several hours after withdrawal from the flower, the main function of which appears to be to reduce the possibility of geitonogamous pollination. Other mechanisms that promote outcrossing and pollen export in orchids include pollen carryover (achieved by sectile or soft pollinia), temporary retention of the anther cap, protandry and self-incompatibility (rare among orchids). Pollinaria ensure that large pollen loads are deposited on the stigma, thus enabling the fertilization of the large numbers of ovules in the flowers of Orchidaceae. Pollinaria also ensure efficient removal of pollen from the anther, minimal pollen wastage during transit, and a high probability of deposition on conspecific stigmas.     

Developmental studies in orchid flowers II: Orchidoid species

The floral development of 11 species of Orchidoideae (sensu Rasmussen 1985) was studied by means of SEM, paying special attention to the early development of the gynostemium and its appendages. In contrast to the staminodes found in epidendroid and vandoid orchids, the 'auricles' of the tribe Orchideae are developed on the dorsal side of the fertile anther and therefore are not interpreted as staminodes. Presumed vestiges of the staminodes corresponding to those of the Epidendroideae and Vandoideae are differentiated in early developmental stages, but remain inconspicuous structures later on. The three-lobed rostellum originates entirely from the median carpel. The outstanding systematic position of the tribe Orchideae is briefly discussed.