Flower structure and development of Araceae compared with alismatids and Acoraceae

Floral development of Araceae is compared with that of other basal monocots such as alismatids and Acorus. Flowers of Araceae, Acorus and several alismatids with spicate inflorescences lack a subtending floral bract. In Araceae and some Potamogetonaceae the subtending floral bract is suppressed, and not incorporated into the perianth. This differs from Acorus and some alismatids, where a bract-like median abaxial tepal is formed in the outer perianth whorl (i.e. developmental merger of flower-subtending bract and tepal). In Araceae, Acorus and spicate alismatids flowers develop unidirectionally, correlated with bract reduction. Araceae lack unidirectionality in the outer perianth whorl, in contrast t o Acorus and Juncaginaceae. The transition from trimerous to dimerous flowers in Onintiurn (Araceae) is by accentuation of the unidirectionality of the inner perianth. The gynoecium of Araceae and Acorus is synascidiate. However, in most Araceae the synascidiate portion is shorter than in Acorns, and a distinct basal elongation phase as in Acorus and Juncaginaceae was not found. The perianth and androecium of Lysichiton and Symplocarpus and the gynoecium of Gymnostachys differ from other Araceae and resemble those in Potamogetonaceae. Developmental findings support the isolation of Acorus from Araceae, and show similarities of Araceae with Potamogetonaceae and of Acorus with Juncaginaceae.     

Study of homeosis in the flower of Philodendron (araceae): a qualitative and quantitative approach

This study deals specifically with floral organogenesis and the development of the inflorescence of Philodendron squamiferum and P. pedatum. Pistillate flowers are initiated on the lower portion of the inflorescence and staminate flowers are initiated on the distal portion. An intermediate zone consisting of sterile male flowers and atypical bisexual flowers with fused or free carpels and staminodes is also present. This zone is located between the sterile male and female floral zones. In general, the portion of bisexual flowers facing the male zone forms staminodes, and the portion facing the female zone develops an incomplete gynoecium with few carpels. The incomplete separation of some staminodes from the gynoecial portion of the whorl shows that they belong to the same whorl as the carpels. There are two levels of aberrant floral structures in Philodendron: The first one is represented by the presence of atypical bisexual flowers, which are intermediates between typical female flowers and typical sterile male flowers. The second one is the presence of intermediate structures between typical carpels and typical staminodes on a single atypical bisexual flower. The atypical bisexual flowers of P. squamiferum and P. pedatum are believed to be a case of homeosis where carpels have been replaced by sterile stamens on the same whorl. A quantitative analysis indicates that in both species, on average, one staminode replaces one carpel.     

Homeosis in Araceae Flowers: The Case of Philodendron melinonii

The early stages of development of the inflorescence of Philodendronmelinonii were examined using scanning electron microscopy.Pistillate flowers are initiated on the lower portion of theinflorescence and staminate flowers are initiated on the distalportion. The male flowers have four to five stamens. The femaleflowers have a multilocular ovary consisting of four to sixlocules. A transition zone consisting of sterile male flowersand bisexual flowers with fused or free carpels and staminodesis also present on the inflorescences. This zone is locatedbetween the male and female flower zones. Generally, the portionof the bisexual flower facing the male zone forms stamens, andthe portion facing the female zone develops an incomplete gynoeciumwith few carpels. In P. melinonii, the incomplete separationof staminodes from the gynoecial portion of the whorl showsthat the staminodes and carpels belong to the same whorl. Thebisexual flowers of P. melinonii are believed to be a case ofhomeosis where carpels have been replaced by sterile stamenson the same whorl. At the level of the inflorescence, pistillateand staminate flowers are inserted on the same contact parastichiesalong the inflorescence; there is no discontinuity between thefemale zone, the bisexual zone, and the male zone. The presenceof bisexual flowers is believed to correspond to a morphogeneticgradient at the level of the inflorescence as a whole. Copyright2000 Annals of Botany Company Flower, development, gradient, inflorescence     

Floral organogenesis in Tetracentron sinense (Trochodendraceae) and its systematic significance

In Tetracentron sinense of the basal eudicot family Trochodendraceae, the flower primordium, together with the much retarded floral subtending bract primordium appear to form a common primordium. The four tepals and the four stamens are initiated in four distinct alternating pairs, the first tepal pair is in transverse position. The four carpels arise in a whorl and alternate with the stamens. This developmental pattern supports the interpretation of the flower as dimerous in the perianth and androecium, but tetramerous in the gynoecium. There is a relatively long temporal gap between the initiation of the stamens and the carpels. The carpel primordia are then squeezed into the narrow gaps between the four stamens. In contrast to Trochodendron, the residual floral apex after carpel formation is inconspicuous. In their distinct developmental dimery including four tepals and four stamens, flowers of Tetracentron are reminiscent of other, related basal eudicots, such as Buxaceae and Proteaceae.     

Developmental morphology of the flower of <Emphasis Type="Italic">Dracontium polyphyllum</Emphasis> in the context of the phylogeny of the Araceae

The inflorescence of Dracontium polyphyllum consists of 150 – 300 flowers arranged in recognisable spirals. The flower has 5 – 6 (90% of observed specimens), or 7 broad tepals enclosing 9 – 12 stamens (occasionally 7) inserted in two whorls. The gynoecium is trilocular (90% of observed specimens) or tetralocular. The tetralocular gynoecia are found at random among the trilocular gynoecia. Each locule encloses an ovule inserted in an axile position, in the median portion of the ovary. Each carpel has its own stylar canal. However, in the upper portion of the style, there is only one common stylar canal. Floral organs are initiated in an acropetal direction in the following sequence: tepals, stamens, and carpels. During later stages of development, the tepals progressively cover the other floral organs. The first floral primordia are initiated on the upper portion of the inflorescence. During early stages of development, the floral primordia have a circular shape. The tepals are initiated nearly simultaneously. During later stages of development, the first whorl of stamens develops in alternation with the tepals and is followed by a second whorl of stamens. The trilocular or tetralocular nature of the ovary is clearly visible during early stages of development of the gynoecium. Recent molecular studies show that Anaphyllopsis A. Hay and Dracontium L. are closely related. However, although pentamerous flowers have been observed in Anaphyllopsis, the developmental morphology of the flower of Dracontium is different from that of Anaphyllopsis.     

商陆属植物的花器官发生

为进一步研究商陆科的系统位置提供花器官发生和发育的证据,在扫描电子显微镜下观察了商陆Phytolacca acinosa、多雄蕊商陆P. polyandra和垂序商陆P. americana的花器官发生.结果表明: 商陆属植物花被的发生均为2/5型螺旋发生.在同一个种不同的花蕾中,花被的发生有两种顺序:逆时针方向和顺时针方向.远轴侧非正中位的1枚先发生.雄蕊发生于环状分生组织.在单轮雄蕊的种中8-10枚雄蕊为近同时发生;两轮雄蕊的种8枚内轮雄蕊先发生,6-8枚外轮雄蕊随后发生,内轮雄蕊为同时发生,外轮雄蕊发生次序不规则.心皮原基也发生于环状分生组织,8-10枚心皮原基为同时发生.在后来的发育过程中,商陆的心皮发育成近离生心皮雌蕊;其他2种心皮侧壁联合发育成合生心皮雌蕊.对商陆属植物花器官发生的类型及发育形态学做了分析,结果支持商陆科在石竹目系统发育中处于原始地位的观点.     

RE-EVALUATION OF CERTAIN KEY RELATIONSHIPS IN THE ALISMATIDAE: FLORAL ORGANOGENESIS OF SCHEUCHZERIA PALUSTRIS (SCHEUCHZERIACEAE)

Transition to flowering in the North-temperate bog plant Scheuchzeria palustris occurs in early May and results in the formation of a simple raceme with six flowers. Five of the flowers are subtended by large foliar bracts, while the sixth and last-formed flower on the inflorescence remains ebracteate. The individual flowers develop along a clearly trimerous pattern. The three outer tepals develop first, arising almost simultaneously at the periphery of the triangular floral apex. They are followed closely by the development of the three anti-tepalous outer stamens. The three inner tepals are next in the developmental sequence, alternating with the outer whorl of tepal-stamen pairs but arising at a slightly higher level on the floral meristem. Three inner stamens are initiated opposite the inner tepal primordia. Finally, three gynoecial primordia are initiated on the remaining central portion of the floral apex and alternating with the inner whorl of tepal-stamen pairs. Each carpel develops at first as a horseshoe-shaped structure. Two ovules form in each carpel, initiating on the adaxial margin of the carpel wall. Histogenesis of all floral appendages involves initially periclinal divisions in the second tunica layer followed by corresponding anticlinal divisions in the first tunica layer and concurrent activity in the underlying corpus. Separate procambial strands differentiate acropetally from the inflorescence axis to each tepal-stamen pair and then bifurcate. The vascular connection to the gynoecium develops directly from the strands in the tepal-stamen pairs. The results of this developmental study of the flower of S. palustris have a significant bearing on the positioning of this and related taxa within the Alismatidae and on the speculation of the phylogeny of the monocotyledon flower.     

Origin and variation of polymerous gynoecia in Fabaceae: evidence from floral mutants of pea (Pisum sativum L.)

Polymerous gynoecia are normally found in some members of Fabaceae, although the vast majority of this family is characterized by a gynoecium consisting of a single carpel. Summarizing the variation of gynoecium features in these species together with analysis of floral structure and ontogeny in mutants of pea (Pisum sativum L.) suggests to propose two different ways of gynoecium polymerization in legumes. The first is homeotic replacement of the stamens into carpels observed in stp mutants of pea and possibly causing the multicarpellate habit in mimosoids. The second deals with flower fusion within an inflorescence, a transformation observed in fasciated forms of pea together with the mutants coch and det. Similar processes might contribute to formation of the bicarpellate flowers of some swartzioid legumes. The polymerous gynoecium evolved in Fabaceae at least twice independently.     

Female flower and fruit anatomy of Tetroncium magellanicum: implications for gynoecium evolution in the early divergent monocot order Alismatales

Female flower and fruit anatomy, including vasculature, are studied for the first time in Tetroncium (Juncaginaceae: Alismatales). Other members of Juncaginaceae (and the relatively close Maundiaceae) possess a peculiar type of gynoecium with pronounced carpel fusion via the floral centre. Their carpels are supplied by individual vascular traces and can be interpreted either as synascidiate (if viewed as horizontally inserted) or free and plicate (if viewed as obliquely inserted on an elongated receptacle). In Tetroncium, the gynoecium is tetracarpellate and clearly has a well‐developed synascidiate zone with septa formed by united flanks of adjacent carpels. The gynoecium of Tetroncium is supplied by a common ring of vascular tissue that splits into dorsal and heterocarpellary ventral (synventral) bundles, a condition that can be expected in a typical syncarpous gynoecium. The fruit is indehiscent and contains one or two seeds. The syncarpy of Tetroncium is of functional significance for fruit formation, as it allows the thin septa to be distorted, thus providing more space for the developing seed(s). The occurrence of typical syncarpy in Tetroncium provides further evidence for the highly homoplastic evolution of gynoecium characters in the early‐divergent monocot order Alismatales. Either the similarity between gynoecia of Maundiaceae and Triglochin (Juncaginaceae) is due to parallel evolution or the syncarpy of Tetroncium should be viewed as secondarily derived. In the latter scenario, fusion via the floral centre is probably a synapomorphy of core Alismatales (Helobiae) and more typical syncarpy evolved independently in several lineages, such as Scheuchzeria, Tetroncium and Butomus/Hydrocharitaceae. In total, Tetroncium differs from other Juncaginaceae in 13 structural characters, including ensiform leaves that are similar to those of Tofieldiaceae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 712–724.     

Comparative floral structure and systematics in Chrysobalanaceae s.l. (Chrysobalanaceae, Dichapetalaceae, Euphroniaceae, Trigoniaceae; Malpighiales)

Chrysobalanaceae s.l. , one of the few suprafamilial subclades of Malpighiales that is supported by molecular phylogenetic analyses, and containing Chrysobalanaceae, Dichapetalaceae, Euphroniaceae, and Trigoniaceae, was comparatively studied with regard to floral structure. The subclade is well supported by floral structure. Potential synapomorphies for Chrysobalanaceae s.l. are the following shared features: floral cup; flowers obliquely monosymmetric; sepals congenitally united at base; sepals of unequal size (outer two shorter); fertile stamens concentrated on the anterior side of the flower and sometimes united into a strap; staminodes absent in the posteriormost antepetalous position; anthers extremely introrse, with thecae almost in one plane; endothecium continuous over the dorsal side of the connective; dorsal anther pit; gynoecium completely syncarpous up to the stigma; carpel flanks slightly bulged out transversely and thus carpels demarcated from each other by a longitudinal furrow; flowers with dense unicellular, non-lignified hairs, especially on the gynoecium; light-coloured, dense indumentum on young shoots and inflorescences. Potential synapomorphies for Chrysobalanaceae + Euphroniaceae include: spur in floral cup; clawed petals; lignified hairs on petals; nectary without lobes or scales and mostly annular. Potential synapomorphies for Dichapetalaceae + Trigoniaceae include: special mucilage cells in sepals in mesophyll (in addition to epidermis); anthers almost basifixed; gynoecium synascidiate up to lower style; nectary with lobes or scales and semi-annular.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 249–309.     

Zur Entwicklung des Gynoeceums beiBergenia cordifolia (Saxifragaceae)

Scanning electron microscopical investigations of flower buds of the perennial herbBergenia cordifolia (Haw.)A. Br. (Saxifragaceae) reveal a primitive gynoecium. During ontogenesis the margins of the carpel lamina transgress on the apical cone of the axis by meristem incorporation and finally fuse with the margins of the opposite carpel. These processes of meristem incorporation and fusion first lead to gamophylly and furthermore to carpel peltation, as is demonstrated by SEM-photographs (ring-shaped dike and common septum of the two carpels). As a result of carpel peltation, the lowest point of the septum deliminates the synascidiate zone. Above this point, the symplicate and, eventually, the plicate zone follows (vid. ventral suture). The margins of the carpel lamina merely touch each other without being coalesced. The preparation of a window in the carpel's dorsal side permits a look at a massive lateral placenta (Leinfellner 1951) developing the ovules. In the lower third—in lateral position at the placenta's margin—the first ovules are seen, the next ones follow in acropetal and basipetal direction, as well as to the periphery of the placenta.

     

Hormonal changes during flower development in floral tissues of Lilium

Much effort has been focussed on better understanding the key signals that modulate floral senescence. Although ethylene is one of the most important regulators of floral senescence in several species, Lilium flowers show low sensitivity to ethylene; thus their senescence may be regulated by other hormones. In this study we have examined how (1) endogenous levels of hormones in various floral tissues (outer and inner tepals, androecium and gynoecium) vary throughout flower development, (2) endogenous levels of hormones in such tissues change in cut versus intact flowers at anthesis, and (3) spray applications of abscisic acid and pyrabactin alter flower longevity. Results show that floral tissues behave differently in their hormonal changes during flower development. Cytokinin and auxin levels mostly increased in tepals prior to anthesis and decreased later during senescence. In contrast, levels of abscisic acid increased during senescence, but only in outer tepals and the gynoecium, and during the latest stages. In addition, cut flowers at anthesis differed from intact flowers in the levels of abscisic acid and auxins in outer tepals, salicylic acid in inner tepals, cytokinins, gibberellins and jasmonic acid in the androecium, and abscisic acid and salicylic acid in the gynoecium, thus showing a clear differential response between floral tissues. Furthermore, spray applications of abscisic acid and pyrabactin in combination accelerated the latest stages of tepal senescence, yet only when flower senescence was delayed with Promalin. It is concluded that (1) floral tissues differentially respond in their endogenous variations of hormones during flower development, (2) cut flowers have drastic changes in the hormonal balance not only of outer and inner tepals but also of androecium and gynoecium, and (3) abscisic acid may accelerate the progression of tepal senescence in Lilium.     

INFLORESCENCE AND FLORAL DEVELOPMENT IN HOUTTUYNIA CORDATA (SAURURACEAE)

The inflorescence of Houttuynia cordata produces 45–70 sessile bracteate flowers in acropetal succession. The inflorescence apical meristem has a mantle-core configuration and produces “common” or uncommitted primordia, each of which bifurcates to form a floral apex above, a bract primordium below. This pattern of organogenesis is similar to that in another saururaceous plant, Saururus cernuus. Exceptions to this unusual development, however, occur in H. cordata at the beginning of inflorescence activity when four to eight petaloid bract primordia are initiated before the initiation of floral apices in their axils. “Common” primordia also are lacking toward the cessation of inflorescence apical activity in H. cordata when primordia become bracts which may precede the initiation of an axillary floral apex. Many of these last-formed bracts are sterile. The inflorescence terminates with maturation of the meristem as an apical residuum. No terminal flowers or terminal gynoecia were found, although subterminal gynoecia or flowers in subterminal position may overtop the actual apex and obscure it. Individual flowers have a tricarpellate syncarpous gynoecium and three stamens adnate to the carpels; petals and sepals are lacking. The order of succession of organs is: two lateral stamens, median stamen, two lateral carpels, median carpel. The three carpel primordia almost immediately are elevated as part of a gynoecial ring by zonal growth of the receptacle below the attachment of the carpels. The same growth elevates the stamen bases so that they appear adnate to the carpels. The trimerous condition in Houttuynia is the result of paired or solitary initiations rather than trimerous whorls. Symmetry is bilateral and zygomorphic rather than radial. No evidence of spiral arrangement in the flower was found.     

海韭菜的花器官发生

运用扫描电镜（SEM）观察了海韭菜（Triglochin maritimum）的花器官发生发育过程。结果表明：海韭菜花发育是典型的单子叶植物发生模式,即两轮花被片、两轮雄蕊和两轮心皮以三基数轮状交替发生,花器官是以向心向顶的方式发生的,未发现“花被片—雄蕊复合原基”。 发育后期雄蕊和与之对生的花被片之间的共同基部可能是相继向上居间生长的结果。花被片轮和雄蕊轮二者之间在发育位置、时间和速率上存在差异,内轮花被片原基和外轮雄蕊原基的不同发育时间和发育速度使得在成熟花中内轮花被片位于外轮雄蕊的内方。观察结果不支持水麦冬属植物的花是退化（或压缩）的花序侧分枝等假花的观点。     

Comparative floral structure and systematics in Crossosomatales (Crossosomataceae, Stachyuraceae, Staphyleaceae, Aphloiaceae, Geissolomataceae, Ixerbaceae, Strasburgeriaceae)

Floral structure of all putative families of Crossosomatales as suggested by molecular studies was comparatively studied. The seven comprise Crossosomataceae, Stachyuraceae, Staphyleaceae, Aphloiaceae, Geissolomataceae, Ixerbaceae, and Strasburgeriaceae. The entire clade (1) is highly supported by floral structure, also the clades (in sequence of diminishing structural support): Ixerbaceae/Strasburgeriaceae (2), Geissolomataceae/Ixerbaceae/Strasburgeriaceae (3), Aphloiaceae/Geissolomataceae/Ixerbaceae/Strasburgeriaceae (4), and Crossosomataceae/Stachyuraceae/Staphyleaceae (5). Among the prominent floral features of Crossosomatales (1) are solitary flowers, presence of a floral cup, imbricate sepals with outermost smaller than inner, pollen grains with horizontally extended endoapertures, shortly stalked gynoecium, postgenitally united carpel tips forming a compitum, stigmatic papillae two‐ or more‐cellular, ovary locules tapering upwards, long integuments forming zigzag micropyles, cell clusters with bundles of long yellow crystals, mucilage cells, seeds with smooth, sclerified testa and without a differentiated tegmen. Clade (2) is characterized by large flowers, petals forming a tight, pointed cone in bud, stamens with long, stout filaments and sagittate anthers, streamlined, conical gynoecium, antitropous ovules, rudimentary aril, lignified, unicellular, T‐shaped hairs and idioblasts with striate mucilaginous cell walls. Clade (3) is characterized by alternisepalous carpels, punctiform stigma formed by postgenitally united and twisted carpel tips, synascidiate ovary, only one or two pendant ovules per carpel, nectary recesses between androecium and gynoecium. Clade (4) is characterized by pronounced ‘pollen buds’. Clade (5) is characterized by polygamous or functionally unisexual flowers, x‐shaped anthers, free and follicular carpels (not in Stachyuraceae). Crossosomataceae and Aphloiaceae, although not retrieved as a clade in molecular studies, share several special floral features: polystemonous androecium; basifixed anthers without a connective protrusion; stigma with two more or less decurrent crests; camplyotropous ovules and reniform seeds; simple, disc‐shaped nectaries and absence of hairs. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 147 , 1–46.     

Morphology and development of the female flowers in Geonoma interrupta (Arecaceae)

Morphology and development of the female flowers in Geonoma interrupta are described and compared with other taxa within Arecaceae. Inflorescences are pleiothyrses. Cincinni are immersed in pits and arranged according to the Fibonacci pattern along the rachillae. The gynoecium is composed of three free carpels in early stages and later becomes pseudomonomerous. Two carpels are sterile; they develop to different degrees and are commonly unequal in size. The fertile carpel contains a single, crassinucellate, anatropous ovule. Styles are formed in each carpel. The style of the fertile carpel becomes basifixed as the ovary enlarges. The stigmas remain free and plicate during development and expose unicellular papillae at anthesis. Pollen tube transmitting tracts and a compitum are present in the ventral slits of the stigmas and the postgenitally united styles during anthesis. A septal nectary is formed by incomplete union of the flanks of the carpels at the base of the gynoecium, and nectar is secreted from an epithelium. It is suggested that in Geonoma as a whole, the attraction of pollinators to female flowers is due to a combination of nectar reward and partial mimicry of male flowers.     

Meristic variation in Potamogeton flowers

Flowers of Potamogeton normally have a completely tetramerous plan. Deviations from this norm occur quite commonly in the uppermost flowers of the inflorescence; these variations have been reported before and usually involve a reduction in number of parts. Cases have now been found where the gynoecium of all or many flowers differs from the normal tetracarpellate arrangement; some species regularly have fewer and others more than four carpels. The developmental bases of meristic variation have been explored and quantitative studies of gynoecia and developing gynoecia have been undertaken. The data are used to evaluate the control and correlation of floral development in Potamogeton in general, and in particular the relationship between the gynoecium and the rest of the flower. The developing flower passes through two successive phases of organ initiation: one in which the perianth and stamen primordia arise, and one in which the gynoecial primordia arise. There seems to be little developmental relationship between the two phases except phyllotactic continuity. During the perianth/stamen phase each stamen primordium arises directly above a perianth member, and the presence of a perianth member seems to be a prerequisite for initiation of the stamen. The perianth/stamen phase seems to be rather stable so that normally four perianth/stamen associations are initiated, except in flowers at the tip of the inflorescence. In the gynoecial phase the number of carpel primordia initiated seems to depend on the relative size of carpel primordia and floral apex, and on whether or not the floral apex continues to grow while initiating carpel primordia.     

Structural features of <Emphasis Type="Italic">Rhododendron luteum</Emphasis> flower

The flower of Rhododendron luteum (L.) Sweet has a pentamerous structure with radial symmetry. The anthers filament surface is covered by dense non-glandular hairs to the half of the height. The tubular anther dehisces along creating two openings in the anther-sac walls and the viscous pollen is released through two splits along the anther lobes. The pistil is pentamerous and the axial channel is filled with a mucilaginous secretion product which is continuous with the exudate on the stigma surface. The stigmatic papillae are densely packed and their exudate is stained intensively red for carbohydrates, while pollen grains are stained positively for lipids. The five-locular ovary has isomerous carpels (syncarpous gynoecium) and the ovary surface is covered by numerous, densely-packed glandular and non-glandular hairs protecting the nectar against transpiration. Numerous ovules per locule occur with one integument and a thin-walled megasporiangium. In carpels, oil cells occur sporadically as solitary idioblasts, located around the vascular bundles. Transmitting tissue cells contain a large central, electron translucent vacuole, filling most of the cell containing dark osmiophilic bodies homogenous or granular in appearance.     

Floral anatomy and systematics of Bretschneidera (Bretschneideraceae)

External morphology and anatomy of the flower and pollen of Bretschneidera sinensis Hemsl. are described to clarify the position of the family Bretschneideraceae relative to the Sapindales and the glucosinolate-producing families. Anatomical and micromorphological characters are investigated and sections are used to understand the structure of the flower. Observation of buds and sections reveal that the flower is obliquely monosymmetric, with the symmetry line running from one petal to a sepal. The upper petal shields the stamens and pistil and becomes positioned apically by the partial resupination of the pedicel. The octomerous androecium is characterized by variable empty positions which are related to the variable insertion of the three carpels. The loss of stamens is linked with a displacement of the remaining stamens. Floral anatomy demonstrates the presence of a nectary extending on the hypanthium from the base of the filaments to the base of the gynoecium. Details of floral anatomy are compared with members of Sapindaceae, Hippocastanaceae, Moringaceae, Akaniaceae, Tropaeolaceae and Capparaceae. Comparison with other characters supports a close relationship with Akaniaceae and Tropaeolaceae in an order Tropaeolales, in concordance with macromolecular results, either at the base of the glucosinolate clade, or in remote connection with the Sapindales. A number of floral anatomical characters with a strong phylogenetic signal are highlighted. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 29–45.