Floral ontogeny of Annonaceae: evidence for high variability in floral form

Background and Aims

Annonaceae are one of the largest families of Magnoliales. This study investigates the comparative floral development of 15 species to understand the basis for evolutionary changes in the perianth, androecium and carpels and to provide additional characters for phylogenetic investigation.

Methods

Floral ontogeny of 15 species from 12 genera is examined and described using scanning electron microscopy.

Key Results

Initiation of the three perianth whorls is either helical or unidirectional. Merism is mostly trimerous, occasionally tetramerous and the members of the inner perianth whorl may be missing or are in double position. The androecium and the gynoecium were found to be variable in organ numbers (from highly polymerous to a fixed number, six in the androecium and one or two in the gynoecium). Initiation of the androecium starts invariably with three pairs of stamen primordia along the sides of the hexagonal floral apex. Although inner staminodes were not observed, they were reported in other genera and other families of Magnoliales, except Magnoliaceae and Myristicaceae. Initiation of further organs is centripetal. Androecia with relatively low stamen numbers have a whorled phyllotaxis throughout, while phyllotaxis becomes irregular with higher stamen numbers. The limits between stamens and carpels are unstable and carpels continue the sequence of stamens with a similar variability.

Conclusions

It was found that merism of flowers is often variable in some species with fluctuations between trimery and tetramery. Doubling of inner perianth parts is caused by (unequal) splitting of primordia, contrary to the androecium, and is independent of changes of merism. Derived features, such as a variable merism, absence of the inner perianth and inner staminodes, fixed numbers of stamen and carpels, and capitate or elongate styles are distributed in different clades and evolved independently. The evolution of the androecium is discussed in the context of basal angiosperms: paired outer stamens are the consequence of the transition between the larger perianth parts and much smaller stamens, and not the result of splitting. An increase in stamen number is correlated with their smaller size at initiation, while limits between stamens and carpels are unclear with easy transitions of one organ type into another in some genera, or the complete replacement of carpels by stamens in unisexual flowers.     

The floral development of Popowia whitei (Annonaceae)

A study of the floral ontogeny of Popowia was carried out to investigate the phyllotactic arrangement of the floral organs and occurring trends in the androecium of Annonaceae. The flower buds arise on a common stalk in the axil of a bract. Three sepals emerge in quick succession and are rapidly overrun in size by two whorls of petals. The androecium is initiated centripetally in successive whorls. A first whorl of three pairs of outer staminodes emerges opposite the outer petals and is followed by nine staminodes. Next a whorl of nine fertile stamens arises in alternation with the second whorl of staminodes. The carpels arise in three alternating whorls of nine. The nature of the perianth parts is morphologically identical. The process of cyclisation of the androecium from a spiral is discussed for Annonaceae and Magnoliidae in general. The inception of the three outer stamen pairs is a widespread reductive step for multistaminate androecia in the process of oligomerization. It is proposed to define the cyclic inception of numerous stamens as whorled polyandry, being an intermediate step between true polyandry and a reduced stamen number in whorls. The absence of a cup-like shape in the carpel development is related to the flattened receptacle.     

蓝堇草属(毛茛科)花形态发生的扫描电子显微镜观察

花的发生和发育过程研究可以发现早期进化的轨迹,为系统发育的研究提供重要线索。蓝堇草属(Leptopyrum)为毛茛科唐松草亚科一单种属,仅包含蓝堇草一种,其花的发生和发育过程仍为空白。为了深入理解唐松草亚科乃至毛茛科花发育多样性和演化规律,该文运用扫描电子显微镜(SEM)观察了蓝堇草各轮花器官的形态发生和发育过程。结果表明:该属植物所有的萼片、花瓣、雄蕊和雌蕊均为螺旋状发生,花器官排列式样也为螺旋状; 5枚萼片原基宽阔,5枚花瓣原基圆球形、位于萼片原基的间隔,且在后期表现为延迟发育现象,雄蕊原基较小、为圆球形; 花瓣原基和雄蕊原基连续发生,无明显的时空间隔,但与萼片原基有时空间隔; 心皮原基为马蹄形对折,柱头组织由单细胞乳突组成; 胚珠倒生、具单珠被。该属花器官螺旋状排列、胚珠具单珠被在唐松草亚科中是独有的性状,花发育形态学证据支持了该属的特殊性。     

The role of inner staminodes in the floral display of some relicMagnoliales

The inner staminodes (between stamens and carpels) in some relicMagnoliales (Austrobaileyaceae, Degeneriaceae, Eupomatiaceae, andHimantandraceae) are not just reduced stamens; they are very elaborate organs. InEupomatiaceae, Himantandraceae, and probablyDegeneriaceae they have their own secretory structures which do not occur on the stamens. These play an important role in floral biology. They contribute to the floral coloration pattern; they effect herkogamy by their position and by movements; they provide shelter and food tissue and food secretions (?) for pollinating beetles; they secrete odouriferous oils, mucilage (probably for pollen adherence) and water or nectar (?). For theHimantandraceae a new secretory region on the base of the inner staminode is described. These complicated inner staminodes are extreme specializations of primitive floral types. They have no counterparts in more advanced subclasses of the angiosperms.     

Floral development of Berberidopsis corallina: a crucial link in the evolution of flowers in the core Eudicots

BACKGROUND AND AIMS: On the basis of molecular evidence Berberidopsidaceae have been linked with Aextoxicaceae in an order Berberidopsidales at the base of the core Eudicots. The floral development of Berberidopsis is central to the understanding of the evolution of floral configurations at the transition of the basal Eudicots to the core Eudicots. It lies at the transition of trimerous or dimerous, simplified apetalous forms into pentamerous, petaliferous flowers. METHODS: The floral ontogeny of Berberidopsis was studied with a scanning electron microscope. KEY RESULTS: Flowers are grouped in terminal racemes with variable development. The relationship between the number of tepals, stamens and carpels is more or less fixed and floral initiation follows a strict 2/5 phyllotaxis. Two bracteoles, 12 tepals, eight stamens and three carpels are initiated in a regular sequence. The number of stamens can be increased by a doubling of stamen positions. CONCLUSIONS: The floral ontogeny of Berberidopsis provides support for the shift in floral bauplan from the basal Eudicots to the core Eudicots as a transition of a spiral flower with a 2/5 phyllotaxis to pentamerous flowers with two perianth whorls, two stamen whorls and a single carpel whorl. The differentiation of sepals and petals from bracteotepals is discussed and a comparison is made with other Eudicots with a similar configuration and development. Depending on the resolution of the relationships among the basalmost core Eudicots it is suggested that Berberidopsis either represents a critical stage in the evolution of pentamerous flowers of major clades of Eudicots, or has a floral prototype that may be at the base of evolution of flowers of other core Eudicots. The distribution of a floral Bauplan in other clades of Eudicots similar to Berberidopsidales is discussed.     

The evolution of floral biology in basal angiosperms

In basal angiosperms (including ANITA grade, magnoliids, Choranthaceae, Ceratophyllaceae) almost all bisexual flowers are dichogamous (with male and female functions more or less separated in time), and nearly 100 per cent of those are protogynous (with female function before male function). Movements of floral parts and differential early abscission of stamens in the male phase are variously associated with protogyny. Evolution of synchronous dichogamy based on the day/night rhythm and anthesis lasting 2 days is common. In a few clades in Magnoliales and Laurales heterodichogamy has also evolved. Beetles, flies and thrips are the major pollinators, with various degrees of specialization up to large beetles and special flies in some large-flowered Nymphaeaceae, Magnoliaceae, Annonaceae and Aristolochiaceae. Unusual structural specializations are involved in floral biological adaptations (calyptras, inner staminodes, synandria and food bodies, and secretory structures on tepals, stamens and staminodes). Numerous specializations that are common in monocots and eudicots are absent in basal angiosperms. Several families are poorly known in their floral biology.     

FLORAL DEVELOPMENT OF HYDROCHARIS MORSUS-RANAE (HYDROCHARITACEAE)

In both male and female flowers of H. morsus-ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.     

Floral phyllotaxis in basal angiosperms: development and evolution

To date, molecular developmental studies have focused on vegetative rather than floral phyllotaxis because vegetative shoot apices are technically more tractable than floral apices in model plants. In contrast to evolutionary changes in the phyllotaxis of vegetative shoots, however, changes in floral phyllotaxis appear to have played a major role in angiosperm evolution. Consolidation of a whorled floral phyllotaxis in derived groups allowed synorganization of floral organs and further adaptive radiations. In basal angiosperms, floral phyllotaxis is more flexible. To study these phenomena, we need clarification of the complex relations of both spiral and whorled phyllotaxis with divergence angles, plastochrons, spiral versus simultaneous initiation of organs, parastichies, orthostichies, organ series, and whorls. Improved resolution of phylogenetic relationships and increased knowledge of the diversity of floral phyllotaxis will allow us to trace evolutionary changes in floral phyllotaxis in ever more detail. Already, such surveys have confirmed that floral phyllotaxis was unusually labile early in angiosperm evolution. Whether the original floral phyllotaxis in angiosperms was spiral or whorled is equivocal, but it appears that spiral floral phyllotaxis in Magnoliales and Laurales is derived rather than primitive.     

Floral development in Adonideae (Ranunculaceae)

Floral development and floral phyllotaxis in species of Adonis, Callianthemum, and Trollius (Ranunculaceae) were studied with scanning electron microscopy. The floral organs are initiated in spiral sequence and the flowers have spiral phyllotaxis. The sepal primordia are broad, crescent-shaped, and truncate, but those of petals, stamens, and carpels are rather hemispherical. A relatively long plastochron appears to be present between the last sepal and the first petal as compared with the short and equal plastochrones of all subsequent floral organs. Maturation of the stamens within the androecium appears to be centripetal. The carpels have a short ascidiate zone. Placentation is uniformly lateral, even in Adonis and Callianthemum, which have only one fertile ovule per carpel (versus median in other genera of Ranunculoideae with a single fertile ovule). In Adonis and Callianthemum at the tip of the carpel the ventral slit is gaping and the stigma is broadly exposed, whereas in Trollius the stigma is narrower and more pronouncedly decurrent along the ventral slit. The petals in Callianthemum and Trollius are more conspicuously delayed in development than those in Adonis as compared with sepals and stamens. A short carpel stipe is formed early in Callianthemum but later in Adonis and Trollius. In Trollius farreri (commonly having only five carpels in contrast to other species of Trollius) the carpels form a single (spiral) series. Thus floral development is similar in all three genera and, at a lower level, Adonis and Callianthemum are especially close but have different autapomorphies, which reflects the current classification of the genera.     

爪哇蒙蒿子(Anaxagorea javanica)内轮退化雄蕊形态结构及功能

利用扫描电子显微镜、光学显微镜对爪哇蒙蒿子（Anaxagorea javanica Blume）可育雄蕊、内轮退化雄蕊和雌蕊的形态、结构进行了观察,并利用组织化学染色法对内轮退化雄蕊和柱头顶端腺毛化学成分进行了检测。结果显示,内轮退化雄蕊顶端为长条状腺毛,柱头顶端有头状和盾状腺毛,两者顶端的腺毛形态和结构明显不同,但分泌物成分类似,都含有蛋白质和脂类物质。内轮退化雄蕊的横切面为一层表皮细胞包围着薄壁组织,中央有一束维管束,与可育雄蕊花丝部位的横切面十分相似,是介于可育雄蕊和雌蕊之间的过渡结构。在雌蕊阶段,退化雄蕊顶端腺体释放的黏液供传粉昆虫觅食;在雄蕊阶段,退化雄蕊顶端覆盖柱头,呈S型,防止自花授粉。爪哇蒙蒿子薄片状可育雄蕊、内轮退化雄蕊以及可育雄蕊和退化雄蕊腹面上存在气孔等原始性状,是连接番荔枝科和其外类群的同源特征。     

Comparative floral development in Lardizabalaceae (Ranunculales)

Lardizabalaceae, one of seven families of Ranunculales, represent a monophyletic group. The family has functionally unisexual flowers with the organs in trimerous whorls, petaloid sepals and sometimes nectariferous petals. Among Ranunculales, Lardizabalaceae share several floral characters and climbing habit with Menispermaceae, but molecular analyses indicate that Circaeasteraceae and Lardizabalaceae form a strongly supported clade. Morphological and ontogenetic studies of flowers have proved to be a good complement to molecular data in clarifying relationships. Floral organogenesis has been studied in very few species of the family. This study investigates the comparative floral development of three species from three genera (Decaisnea, Akebia and Holboellia) of Lardizabalaceae using scanning electron microscopy. Flowers have a whorled phyllotaxis. Within each whorl, the organs are initiated either simultaneously or in a rapid spiral sequence. In Akebia, six sepals are initiated, but one to three sepals of the second whorl do not further develop. The presence of three sepals in Akebia is thus a developmentally secondary simplification. The petals (if present) are retarded in early developmental stages; stamens and petals are different in shape from the beginning of development. The retarded petals may not be derived from staminodes in Lardizabalaceae. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 171–184.     

Pseudodiplostemony, and its implications for the evolution of the androecium in the Caryophyllaceae

The androecium of the Caryophyllaceae is varied, ranging from a two-whorled condition to a single stamen. A number of species belonging to the three subfamilies, Caryophyl-loideae, Alsinoideae and Paronychioideae have been studied ontogenetically with the SEM to understand their peculiar androecial development in the broader context of the Caryophyllales alliance. Although patterns of initiation are highly variable among species, there are three ontogenetic modes of stamen initiation: all stamens simultaneous within a whorl, the antepetalous stamens simultaneous and the antesepalous sequentially with a reversed direction, or both whorls sequentially with or without a reversed direction. The most common floral (ontogenetic) sequence of the Caryophyllaceae runs as follows: five sepals (in a 2/5 sequence), the stamens in front of the three inner sepals successively, stamens opposite the two outermost sepals, five antepetalous stamens (simultaneously or in a reversed spiral superimposed on the spiral of the antesepalous stamens), five outer sterile (petaloid) organs arising before, simultaneously or after the antesepalous stamens, often by the division of common primordia. A comparison with the floral configurations of the Phytolaccaceae and Molluginaceae indicates that the outer petaline whorl of the Caryophyllaceae corresponds positionally to the alternisepalous stamens of somePhytolacca, such asP. dodecandra. The difference withP. dodecandra lies in the fact that an extra inner or outer whorl is formed in the Caryophyl-laceae, in alternation with the sepals. A comparable arrangement exists in the Molluginaceae, though the initiation of stamens is centrifugal. A comparison of floral ontogenies and the presence of reduction series in the Caryophyllaceae support the idea that the pentamerous arrangement is derived from a trimerous prototype. Petals correspond to sterillized stamens and are comparable to two stamen pairs opposite the outer sepals and a single stamen alternating with the third and fifth sepals. Petals are often in a state of reduction; they may be confused with staminodes and they often arise from common stamenpetal primordia. The antesepalous stamen whorl represents an amalgamation of two whorls: initiation is reversed with the stamens opposite the fourth and fifth formed sepals arising before the other, while the stamens opposite the first and second formed sepals are frequently reduced or lost. Reductive trends are correlated with the mode of initiation of the androecium, as well as changes in the number of carpels, and affect the antesepalous and antepetalous whorls in different proportions. It is concluded that the androecium of the Caryophyllaceae is pseudodiplos-temonous and is not comparable to diplostemonous forms in the Dilleniidae and Rosidae. The basic floral formula of Caryophyllaceae is as follows: sepals 5—petals 5 (sterile stamens)—antesepalous stamens 3+2—antepetalous stamens 5 gynoecium 5.     

青城细辛的花器官发生

利用扫描电镜观察了青城细辛（Asarum splendens）的花器官发生过程。青城细辛的花器官为轮状结构,向心发生,依次为两轮3基数的花被原基,两轮6基数的雄蕊原基和一轮6基数的心皮原基。两轮花被原基互生,只有外轮（先发生的一轮）花被原基完全发育,而内轮（后发生的一轮）花被原基在发育过程中逐渐退化。两轮雄蕊原基为离心发生：位于内侧的一轮雄蕊原基先发生,每两个原基正对第一轮发生的花被原基,外侧的一轮雄蕊原基后发生,与内轮雄蕊原基互生。心皮与内侧的一轮雄蕊互生。     

青城细辛的花器官发生

利用扫描电镜观察了青城细辛(Asarum splendens)的花器官发生过程。青城细辛的花器官为轮状结构,向心发生,依次为两轮3基数的花被原基,两轮6基数的雄蕊原基和一轮6基数的心皮原基。两轮花被原基互生,只有外轮(先发生的一轮)花被原基完全发育,而内轮(后发生的一轮)花被原基在发育过程中逐渐退化。两轮雄蕊原基为离心发生:位于内侧的一轮雄蕊原基先发生,每两个原基正对第一轮发生的花被原基,外侧的一轮雄蕊原基后发生,与内轮雄蕊原基互生。心皮与内侧的一轮雄蕊互生。     

THE DEVELOPMENTAL BASIS OF TRISTYLY IN EICHHORNIA PANICULATA (PONTEDERIACEAE)

Eichhornia paniculata is a tristylous, self-compatible, emergent aquatic. A given plant produces flowers with either long, mid or short styles and two levels of stamens equal in length to the styles not found in that flower. Flowers of each morph have two whorls of three tepals, six stamens and three fused carpels. The six stamens differentiate into two sets of three stamens each. A relatively short set, having either short- or mid-level stamens, occurs on the upper side of the flower, while a relatively long set, having either mid- or long-level stamens, occurs on the lower side. Stamen level depends on differences among stamens in filament length and position of insertion on the floral tube. Floral parts arise in whorls of three, but the two stamen whorls do not form the two sets of stamens found in each mature flower. Instead, stamens from both whorls make up a given set. Floral differences among morphs are not present at flower origin or floral organ initiation. Morphological differences arise first among stamen sets. The two sets within a flower differ prior to meiosis in the size, number, and timing of comparable developmental events in the sporogenous cells. After these initial differences arise, anther size diverges. In later developmental stages differences in filament and floral tube length, cell size, and cell number, as well as differences in the length, cell size, and cell number of styles, develop among morphs. This sequence of developmental events suggests that the genes controlling development in different morphs do not control flower and floral organ initiation but are first morphologically visible in sporogenous cell differentiation.     

Floral morphogenesis in Euptelea (Eupteleaceae, Ranunculales)

BACKGROUND AND AIMS: Based on molecular phylogenetic studies, the unigeneric family Eupteleaceae has a prominent phylogenetic position at or near the base of Ranunculales, which, in turn, appear at the base of eudicots. The aim of the present paper is to reveal developmental features of the flowers and to put the genus in a morphological context with other basal eudicots. METHODS: Flowers in all developmental stages of Euptelea pleiosperma were collected in the wild at intervals of 7-10 d in the critical stages and studied with a scanning electron microscope. KEY RESULTS: Remnants of a perianth are lacking throughout flower development. Floral symmetry changes from monosymmetric to asymmetric to disymmetric during development. Asymmetry is expressed in that the sequence of stamen initiation is from the centre to both lateral sides on the adaxial side of the flower but starting from one lateral side and proceeding to the other on the abaxial side. Despite the pronounced floral disymmetry, a dimerous pattern of floral organs was not found. The carpel primordia arise between the already large stamens and alternate with them. Stamens and carpels each form a somewhat irregular whorl. The carpels are ascidiate from the beginning. The stigma differentiates as two crests along the ventral slit of the ovary. The few lateral ovules alternate with each other. CONCLUSIONS: Although the flowers have some unusual autapomorphies (wind pollination, lack of a perianth, pronounced disymmetry of the floral base, long connective protrusion, long temporal gap between androecium and gynoecium initiation, small space for carpel initiation), they show some plesiomorphies at the level of basal eudicots (free carpels, basifixed anthers, whorled phyllotaxis), and thus fit well in Ranunculales.     

Phylogenetic analysis of Magnoliales and Myristicaceae based on multiple data sets: implications for character evolution

Magnoliales, consisting of six families of tropical to warm-temperate woody angiosperms, were long considered the most archaic order of flowering plants, but molecular analyses nest them among other eumagnoliids. Based on separate and combined analyses of a morphological matrix (115 characters) and multiple molecular data sets (seven variable chloroplast loci and five more conserved genes; 14 536 aligned nucleotides), phylogenetic relationships were investigated simultaneously within Magnoliales and Myristicaceae, using Laurales, Winterales, and Piperales as outgroups. Despite apparent conflicts among data sets, parsimony and maximum likelihood analyses of combined data converged towards a fully resolved and well-supported topology, consistent with higher-level molecular analyses except for the position of Magnoliaceae: Myristicaceae + (Magnoliaceae + (( Degeneria + Galbulimima ) + ( Eupomatia + Annonaceae))). Based on these results, we discuss morphological evolution in Magnoliales and show that several supposedly plesiomorphic traits are synapomorphies of Magnoliineae, the sister group of Myristicaceae (e.g. laminar stamens). Relationships within Annonaceae are also resolved with strong support ( Anaxagorea basal, then ambavioids). In contrast, resolution of relationships within Myristicaceae is difficult and still incomplete, due to a very low level of molecular divergence within the family and a long stem lineage. However, our data provide good evidence that Mauloutchia is nested among other Afro-Malagasy genera, contradicting the view that its androecium and pollen are plesiomorphic  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 125–186.     

Floral development and vasculature in Eriocaulon (Eriocaulaceae) provide insights into the evolution of Poales

Background and AimsFloral developmental studies are crucial for understanding the evolution of floral structures and sexual systems in angiosperms. Within the monocot order Poales, both subfamilies of Eriocaulaceae have unisexual flowers bearing unusual nectaries. Few previous studies have investigated floral development in subfamily Eriocauloideae, which includes the large, diverse and widespread genus Eriocaulon. To understand floral variation and the evolution of the androecium, gynoecium and floral nectaries of Eriocaulaceae, we analysed floral development and vasculature in Eriocaulon and compared it with that of subfamily Paepalanthoideae and the related family Xyridaceae in a phylogenetic context.MethodsThirteen species of Eriocaulon were studied. Developmental analysis was carried out using scanning electron microscopy, and vasculature analysis was carried out using light microscopy. Fresh material was also analysed using scanning electron microscopy with a cryo function. Character evolution was reconstructed over well-resolved phylogenies.Key ResultsPerianth reductions can occur due to delayed development that can also result in loss of the vascular bundles of the median sepals. Nectariferous petal glands cease development and remain vestigial in some species. In staminate flowers, the inner stamens can emerge before the outer ones, and carpels are transformed into nectariferous carpellodes. In pistillate flowers, stamens are reduced to staminodes and the gynoecium has dorsal stigmas.ConclusionsFloral morphology is highly diverse in Eriocaulon, as a result of fusion, reduction or loss of perianth parts. The nectariferous carpellodes of staminate flowers originated first in the ancestor of Eriocaulaceae; petal glands and nectariferous branches of pistillate flowers originated independently in Eriocaulaceae through transfer of function. We present a hypothesis of floral evolution for the family, illustrating a shift from bisexuality to unisexuality and the evolution of nectaries in a complex monocot family, which can contribute to future studies on reproductive biology and floral evolution in other groups.     

Floral development in Anemoneae (Ranunculaceae)

The floral development of two Clematis species and four Anemone species (including Pulsatilla) (Anemoneae, Ranunculaceae) is described. Shared features are: (1) sepals shortly after initiation broad, crescent‐shaped, as opposed to the other organs, which are narrow and hemispherical; (2) outermost organs of the androecium often smaller than the others and sometimes sterile; (3) carpels ascidiate, with distinctive stalk, stigma papillate, decurrent; the carpels have one median fertile ovule and a few lateral sterile ovules in all species studied; the fertile ovule appears before the carpel closes. Generic differences are: (1) In Clematis, four sepals are initiated in two pairs; sometimes one of the sepals in the second pair appears to be divided into two organs (double position) resulting in a pentamerous perianth; the first eight stamens are positioned in two alternating whorls, the outer whorl alternating with the four sepals. In Anemone, the perianth organs, if five, are initiated in spiral sequence; in the Pulsatilla group of Anemone, six sepals are initiated in two whorls; the first three organs of the androecium (staminodes) alternate with the inner sepals. (2) Further androecial organs are mostly in complex whorls (i.e. including double positions) in Clematis, but in an irregular spiral or in irregular complex whorls in Anemone. (3) Anther maturation is largely centripetal in Clematis, but centrifugal or bidirectional in Anemone. In Clematis macropetala, the outermost organs of the androecium lack anthers and the filaments expand and become petal‐like. In contrast, in the Pulsatilla group of Anemone, these organs retain sterile anthers and become small, capitate organs. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 77–100.