Embryology of the Irvingiaceae,a family with uncertain relationships among the Malpighiales

The Irvingiaceae, one of 40 families of the Malpighiales, comprise a small woody family of 10 species in three genera distributed in Old World tropics. Its relationships with other families are unclear, although recent molecular analyses suggest affinities with Linaceae, Caryocaraceae, Erythroxylaceae, and Rhizophoraceae. To gain insight into family relationships, we investigated 63 embryological characters of two previously unstudied African species, Irvingia gabonensis and I. smithii, and compared them with other Malpighiales and the sister group Oxalidales. Embryologically, Irvingia is characterized by the absence of an integumentary tapetum and by having a non-multiplicative inner integument, a multiplicative testa, many discrete fascicles of vascular bundles running in the testa from the raphe to antiraphe (each fascicle comprised several strands arranged in a concentric manner), and a fibrous exotegmen. Comparisons showed that Irvingia did not resemble any of the Linaceae, Caryocaraceae, Erythroxylaceae, Rhizophoraceae, or any of the other malpighialean families for which embryological data are available. The genus rather resembled Huaceae and Connaraceae (Oxalidales) in seed coat structure. However, 18 families (45%) of the Malpighiales are still poorly understood embryologically, and therefore additional studies are required for further critical comparisons.     

Comparative floral structure and systematics in Ochnaceae s.l. (Ochnaceae,Quiinaceae and Medusagynaceae; Malpighiales)

Ochnaceae s.l. (Ochnaceae, Quiinaceae and Medusagynaceae), one of the well‐supported subclades of the large order Malpighiales retrieved so far in molecular phylogenetic studies, were comparatively studied with regard to floral structure using microtome section series and scanning electron microscopy (SEM). Floral morphology, anatomy and histology also strongly reflect this close relationship. Potential synapomorphies of the subclade include: flowers nectarless, sepals of different sizes within a flower, petals not retarded in development and forming the protective organs of advanced floral buds, petal aestivation contort, petals with three vascular traces, petals reflexed over the sepals and directed toward the pedicel, polystemony, anthers almost or completely basifixed, gynoecium often with more than five carpels, short gynophore present, styles separate for at least their uppermost part and radiating outwards, suction‐cup‐shaped stigmas, vasculature forming a dorsal band of bundles in the upper stylar region, gynoecium epidermis with large, radially elongate cells, ovules either weakly crassinucellar or incompletely tenuinucellar with an endothelium, abundance of tanniferous tissues and sclerenchyma in floral organs. The most strongly supported subclade of two of the three families in molecular analyses, Quiinaceae and Medusagynaceae, is also particularly well supported by floral structural features, including the presence of functionally and morphologically unisexual flowers, a massive thecal septum that persists after anther dehiscence, styles radiating outward from the ovary, two lateral ovules per carpel, positioned one above the other, conspicuous longitudinal ribs on the ovary wall at anthesis, and a ‘false endothelium’ on the nucellus at anthesis. Additionally, the group fits well in Malpighiales and further emphasizes the relationship of Malpighiales with Celastrales and Oxalidales, and thus the unity of the COM clade. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 299–392.     

Comparative floral structure and systematics in Celastrales (Celastraceae, Parnassiaceae, Lepidobotryaceae)

Floral morphology, anatomy and histology in the newly circumscribed order Celastrales, comprising Celastraceae, Parnassiaceae and Lepidobotryaceae are studied comparatively. Several genera of Celastraceae and Lepidobotrys (Lepidobotryaceae) were studied for the first time in this respect. Celastraceae are well supported as a group by floral structure (including genera that were in separate families in earlier classifications); they have dorsally bulged‐up locules (and thus apical septa) and contain oxalate druses in their floral tissues. The group of Celastraceae and Parnassiaceae is also well supported. They share completely syncarpous gynoecia with commissural stigmatic lobes (and strong concomitant development of the commissural vascular bundles but weak median carpel bundles), only weakly crassinucellar or incompletely tenuinucellar ovules with an endothelium, partly fringed sepals and petals, protandry in bisexual flowers combined with herkogamy by the movement of stamens and anther abscission, and stamens fused with the ovary. In contrast, Lepidobotryaceae are more distant from the other two families, sharing only a handful of features with Celastraceae (not Parnassiaceae), such as pseudohermaphroditic flowers, united stamen bases forming a collar around the gynoecium and seeds with a conspicuous aril. However, all three families together are also somewhat supported as a group and share petals that are not retarded in late floral bud development, 3‐carpellate gynoecia, ventral slits of carpels closed by long interlocking epidermal cells and pollen tube transmitting tissue encompassing several cell layers, both integuments usually more than two cell layers thick, and only weak or lacking floral indumentum. In some molecular analyses Celastrales form an unsupported clade with Malpighiales and Oxalidales. This association is supported by floral structure, especially between Celastrales and Malpighiales. Among Celastrales, Lepidobotryaceae especially share special features with Malpighiales, including a diplostemonous androecium with ten fertile stamens, epitropous ovules with an obturator and strong vascularization around the chalaza. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 149 , 129–194.     

FLORAL DEVELOPMENT IN MANGROVE RHIZOPHORACEAE

The flowers of mangrove Rhizophoraceae (tribe Rhizophoreae) are adapted to three different pollination mechanisms. Floral development of representative species of all four genera suggests that the ancestral flower of the tribe was unspecialized, with successively initiated whorls of separate sepals, petals, antisepalous stamens, and antipetalous stamens; at its inception, the gynoecium had a united, half-inferior ovary and separate stigmatic lobes. This developmental pattern is found in Rhizophora mangle (wind-pollinated) and Ceriops decandra (insect-pollinated). In Kandelia, all floral organs distal to the sepals are initiated simultaneously, and there has apparently been an evolutionary amplification in the number of stamens to about six times the number of petals. Explosive pollen release evolved independently in C. tagal and in Bruguiera. In the former, all stamens belong to one whorl and arise simultaneously upon a very weakly differentiated androecial ring primordium. In Bruguiera, the androecial ring is pronounced, and two whorls of stamens arise upon it; the primordia of the antisepalous whorl arise first but are closer to the center of the apex than the antipetalous stamen primordia. The antisepalous stamens bend toward and are enclosed by the petals early in development. In all genera, the inferior ovary develops by zonal growth of receptacular tissue; additional intercalary growth above the placenta occurs in Bruguiera. In general, floral specialization is accompanied by an increase in the width of the floral apex compared to the size of the primordia, increasing fusion of the stylar primordia, and decreasing prominence of the superior portion of the ovary. Apparent specializations of petal appendages for water storage, including the presence of sub-terminal hydathodes (previously unreported in any angiosperm), were found in two species in which flowers remain open during the day but were absent from two species normally pollinated at night or at dawn. Distinctive tribal characteristics that may aid in phylogenetic analysis include the mode of development of the inferior ovary; the aristate, bifid, usually fringed petals that individually enclose one or more stamens; the intrastaminal floral disc; and the initially subepidermal laticiferous cell layer in the sepals and ovary.     

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.     

Early floral development of Camellioideae (Theaceae)

The early floral development of Camellioideae was studied. Two major evolutionary lineages were recognized for this subfamily. The earlier evolved lineage (Camellia, Polyspora, and Pyrenaria) has normally 11-14 perianth members, which are initiated in a continuous spiral and are differentiated into sepals and petals at late floral development, and numerous stamens initiated individually and centrifugally on the whole androecial region. The later derived lineage (Franklinia, Hartia, Schima, and Stewartia) has five sepals and five petals arranged in two whorls, and numerous individual stamens originating centrifugally from the five petal-opposed zones. Hartia-Stewartia and Franklinia-Schima further diverged as two branches - the former is characterized by having androecial fascicles and axile-basal placentation. The androecial fascicle is considered to be derived within this subfamily. The latter exhibits a higher degree of carpellary congenital fusion and axile-central placentaion, and as a whole, is concluded to be the most advanced group in the Camellioideae. A taxonomic treatment of the Camellioideae at the tribal level is also proposed.     

Structure and evolution of the androecium in the Malvatheca clade (Malvaceae s.l.) and implications for Malvaceae and Malvales

Androecial development and structure as well as floral vasculature of six selected species of Bombacoideae and of several smaller lineages of the Malvatheca clade (Malvaceae s.l.) were studied. All studied taxa share a similar pattern of androecial development: initially, five antepetalous/antetepalous and five alternipetalous/alternitepalous primary androecial primordia develop on a ring wall. Two elongate secondary androecial primordia form on each antepetalous/antetepalous sector. At anthesis the androecium consists of an androecial tube crowned by five androecial lobes. Each of these lobes is the developmental product of an alternipetalous/alternitepalous primary androecial primordium and its two neighbouring antepetalous/antetepalous secondary androecial primordia. The elongate, sessile androecial units are positioned along the lateral margins of the androecial lobes and in the distal part of the androecial tube. Seen in the light of the most recent studies of floral development and phylogeny of the Malvaceae and the Malvales as a whole, our data indicate that i) elongate, sessile androecial units are ancestral in the Malvatheca clade, that ii) an obdiplostemonous floral ground plan is a synapomorphy for the Malvaceae, and that iii) diplostemony is most likely ancestral in the Malvales.     

Floral morphology and evolution in Anisophylleaceae

TOBE, H. & RAVEN, P. H., 1988. Floral morphology and evolution in Anisophylleaceae. The four genera of Anisophylleaceae ( Anisophyllea, Combretocarpus, Poga , and Polygonanthus ) are very uniform in their floral structures. Characteristic floral features of the family are: flowers small (except for the female flowers of Polygonanthus ), merism nearly fixed (i.e. 3- or 4-mery), petals deeply incised (except in Polygonanthus ), ovary inferior and multi-loculed, ovules few (one or two) per carpel, styles separate, intra- and interstaminal nectariferous tissues present, and floral vasculature simple. Comparisons with related groups support the distinctiveness of Anisophylleaceae, and suggest a close affinity with both Rhizophoraceae and the Myrtales. The presence of incised petals in both groups suggests an especially close relationship between Anisophylleaceae and Rhizophoraceae, while new evidence from comparative floral morphology suggests that Anisophylleaceae occupy an intermediate position between Rhizophoraceae and Myrtales. Within the Anisophylleaceae, Poga and Polygonanthus share several synapomorphies in floral structure, while Combretocarpus is the most divergent genus in the family and is more distantly related to Poga and Polygonanthus . It is uncertain whether Anisophyllea is more closely related to Poga and Polygonanthus or Combretocarpus , because the evidence from comparative floral morphology conflicts with that from embryology; more data from other kinds of characters are needed to resolve this issue.     

Comparative floral structure and systematics of the clade of Lophopyxidaceae and Putranjivaceae (Malpighiales)

In molecular phylogenetic studies, Lophopyxidaceae and Putranjivaceae are well supported as sisters in the large rosid order Malpighiales. As the floral structure of both families is poorly known and the two families have never been compared, the present comparative study was carried out, as part of a larger project on the comparative floral structure of Malpighiales, using microtome section series and scanning electron microscopy (SEM) studies. Similar to other angiosperm clades, it appears that the structure of the ovules is a strong marker for suprafamilial relationships in Malpighiales. Both families have two collateral pendant antitropous ovules per carpel associated with obturators (as in some Euphorbiaceae s.l., to which Putranjivaceae belonged in earlier classifications). However, in contrast with Euphorbiaceae s.l., the ovules are not crassinucellar, but either incompletely tenuinucellar or only weakly crassinucellar with a long and conspicuously slender nucellus and an endothelium, and do not have a nucellar beak, but a normal micropyle, features they share with families other than Euphorbiaceae s.l. among Malpighiales. Other shared features of the two families include the following. The outer sepals tend to be smaller than the inner ones and the sepals do not protect the gynoecium in older buds. Sepals of some taxa have a single vascular trace. A short zone of synsepaly tends to be present. Stamens tend to be antesepalous in haplostemonous flowers. A short gynophore is present. The synascidiate zone extends up to above the placenta, but is restricted to the ovary in taxa with more than one carpel. The micropyle is formed by the inner integument. The ventral carpel slits extend down into the synascidiate zone as postgenitally fused furrows. The carpels have a broad dorsal band of vascular bundles in the style. The overall floral structure of the two families corroborates their sister position well and does not support the earlier association of Putranjivaceae with Euphorbiaceae s.l. or of Lophopyxidaceae with Geraniales–Sapindales–Celastrales, which rely on shared superficial floral similarities. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 404–448.     

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.     

Floral organogenesis of Delavaya toxocarpa (Sapindaceae; Sapindales)

The floral organogenesis and development of Delavaya toxocarpa Franch. (Sapindaceae) were studied under scanning electron microscope and light microscope to determine its systematic position within Sapindaceae. Flowers arise in terminal thyrses. The sepal primordia initiate in a spiral (2/5) sequence, which are not synchronous. The five petal primordia initiate almost synchronously and alternate with sepal primordia. Eight stamens initiate almost simultaneously and their differentiation precedes that of the petals. The last formed petal and one stamen initiate from a common primordium. Mature stamens curve inwards and cover the ovary in bud. The gynoecium begins as a hemispheric primordium on which two carpellary lobes arise simultaneously. Later in development a single gynocium is formed with two locules and two ovules per locule. Floral morphology suggests a closer affinity with Sapindaceae, although certain features of floral ontogenesis are similar to those observed in certain members of the former Hippocastanaceae, such as Handeliodendron.     

Diversity and evolution of floral structure among early diverging lineages in the Ericales

This is a combination of review and original data on floral structure and diversity in the two earliest diverging lineages of the Ericales, i.e. the balsaminoids, comprising Balsaminaceae, Marcgraviaceae and Tetrameristaceae, and the polemonioids, comprising Fouquieriaceae and Polemoniaceae. Each clade is strongly supported in molecular studies, while structural synapomorphies have largely been lacking. For the balsaminoid families, we compare floral morphology, anatomy and histology among selected taxa and find that the entire clade is strongly supported by the shared presence of nectariferous tissue in the floral periphery, thread-like structures on anthers, truncate stigmas, secretion in the ovary, as well as mucilage cells, raphides and tannins in floral tissues. A possible sister group relationship between Balsaminaceae and Tetrameristaceae is supported by the shared presence of post-genital fusion of filaments and ovary and a star-shaped stylar canal. For polemonioids, we document unexpected diversity of floral features in Polemoniaceae, partly providing structural links to Fouquieriaceae. Features include cochlear and quincuncial corolla aestivation, connective protrusions, ventrifixed anthers and nectariferous tissue in the base of the ovary. In addition, we outline future directions for research on floral structure in the Ericales and briefly discuss the general importance of structural studies for our understanding of plant phylogeny and evolution.     

Systematic affinities of Rhizophoraceae and Anisophylleaceae, and intergeneric relationships within Rhizophoraceae, based on chloroplast DNA, nuclear ribosomal DNA, and morphology

A cladistic analysis of sequences from the chloroplast gene rbcL was used to determine the systematic affinities of Rhizophoraceae and Anisophylleaceae. This analysis rejects close relationships of Rhizophoraceae with Celastraceae or Elaeocarpaceae, suggested previously, and identifies Erythroxylaceae as sister group within the Malpighiales, supported by several morphological and anatomical characters. Our molecular results also indicate that Anisophylleaceae are nested within Cucurbitales. Although this placement is novel, this affinity is also well supported by shared morphological characters. Tribal and generic relationships within Rhizophoraceae are evaluated with a combination of six molecular data sets (rbcL, atpB-rbcL intergenic spacer, trnL-trnF intergenic spacer, ITS1, ITS2, and 5.8S) and a morphological data set. These relationships are compared with results from previous morphological cladistic analyses. Against the background of the molecular results, we briefly discuss the evolution of morphological characters traditionally used for tribal subdivision as well as characters presumably significant for adaptation to mangrove habitats, namely, aerial stilt roots and vivipary.     

The Anatomical Structures and Floral Development of Euryale ferox Salisb

The pedicel of E. ferox possesses closed, scattered vascular bundles and contains no cambium. Four main air canals are well developed. Mesophyll of sepal is differentiated into palisade and spongy parenchyma. Petal is simpler in structure than that of sepal with no palisade tissue differentiated. Stamens show a wide varity of shapes; those in the outer whorls are usually petaloid while the inner whorls are of the conventional type bearing four-loculate anthers. Ovary is inferior, multicarpellarv and syncarpous with laminar plancentae in each locule. The flower primordium grows out from the mixed bud. It is enveloped by an axillary scale. The preliminary indication of floral initiation is the periclinal divisions of the second layer of the shoot apex which is closer to the leaf base. By the time a flower primordium becomes 465μm high, the floral parts begin to arise in a continuous acropetal sequences, namely sepals, petals, stamens and carpels successively with initiation of their primordia by periclinal divisions of the second or third layer on the flank of the floral apex respectively. By the fact that the growth of the outer layered cells of the receptacle is faster than those of the inner ones, an epigynous flower and an inferior ovary is thus to be formed. The ventral margin of the carpel has become conduplicately appressed and fused in the lower portion, while the upper part has not been fused, an ovarian canal is appeared from top of the ovary. There is no differentiation of a style. A central receptacular core is found among the carpels. On the basis of anatomical and developmental studies of the floral organs, we suggest that Euryale ferox exhibits a number of most primitive features, such as petaloid stamens, carpel with ovarian canal, elongated receptacle, prominent residual floral apex and laminar placentation. The development of floral parts and characteristics of ovary indicate that genus Euryale is much more similar to Victoria, Nymphae and Nuphar than to Nelumbo and Brasenia.     

Evolutionary loss of sepals and/or petals in detarioid legume taxa Aphanocalyx, Brachystegia, and Monopetalanthus (Leguminosae: Caesalpinioideae)

Floral development using scanning electron microscopy is compared in several taxa of the Brachystegia subtribal group of caesalpinioid tribe Detariae. This group is characterized by missing sepals and/or petals. In Aphanocalyx djumaensis, Monopetalanthus durandii, and two Brachystegia species, one sepal is initiated in median abaxial position. In the first two, one or two additional sepal rudiments may initiate late. Brachystegia species have all five sepals, which remain scalelike. In Aphanocalyx and Monopetalanthus, one petal initiates adaxially and medianly (a position atypical for the first initiated petal in the family); additional petal rudiments may form in lateral sites. In Brachystegia, five petals are initiated unidirectionally on a meristem ring, but all are suppressed after initiation. In all taxa, ten stamens are initiated on a ring meristem: unidirectionally in Monopetalanthus, bidirectionally in Brachystegia, vs. in erratic order in Aphanocalyx. Carpel and petal initiation are concurrent. Different organ whorls overlap in time in Monopetalanthus and Brachystegia. In all, the floral apex characteristically is elongate radially and narrow tangentially after bracteole initiation. Two ontogenetic features, the meristem ring and the radially elongate post-bracteole floral apex, appear to be possible synapomorphies for the Brachystegia group.     

A SCANNING ELECTRON MICROSCOPIC STUDY ON THE INITIATION AND DEVELOPMENT OF FLORAL ORGANS OF BRASSICA NAPUS (CV. WESTAR)

The initiation and development of the floral organs of Brassica napus L. (cv. Westar) were examined using the scanning electron microscope. After transition of the vegetative apex into an inflorescence apex, flower primordia were initiated in a helical phyllotactic pattern. The sequence of initiation of the floral organs in a flower bud was that of sepals, stamens, petals and gynoecium. Of the four sepal primordia, the abaxial was initiated first, followed by the two lateral and finally the adaxial primordium. The four long stamens were initiated simultaneously in positions alternating with the sepals. The two short stamens were initiated basipetal to and outside the long stamens, and opposite the lateral sepals. The petals arose on either side of the two short stamens and the gynoecium was produced from the remainder of the apex. During development, the sepal primordia curved sharply at the tips and tightly enclosed the other organs. Stamen primordia developed tetralobed anthers at an early stage while filament elongation occurred just prior to anthesis. A unique pattern of bulbous cells was present on the abaxial surface of the anther. Growth of petal primordia lagged relative to the other floral organs but expansion was rapid prior to anthesis. The gynoecium primordium was characterized by an invagination early in development. At maturity, there was differentiation of a papillate stigma, an elongated style and a long ovary marked externally by sutures and divided internally by a septum. Distinct patterns of cuticular thickenings were observed on the abaxial and adaxial surfaces of the petals and stamens and on the surface of the style. The patterns were less obvious on the sepals and ovary. Stomata were present on both surfaces of the mature sepals, on the style and restricted areas on the abaxial surface of the anthers and nectaries but were absent from the petals, the adaxial surface of the stamens and the ovary. No hairs were present on any of the floral organs.     

Embryology of tribeDrypeteae, an enigmatic taxon ofEuphorbiaceae

The tribeDrypeteae, whose traditional assignment inPhyllanthoideae ofEuphorbiaceae is now doubtful, is studied embryologically on the basis of a literature survey and examination of six additional species in two of the four constituent genera.Drypeteae are characterized by having several embryological features that are unknown in otherPhyllanthoideae, such as a two- or three-celled ovule archesporium; a thin, two cell-layered parietal layer in the nucellus; no nucellar beak or cap; an early disintegrating nucellar tissue; thick, multiplicative, inner and outer integuments; an endothelium; a few discrete vascular bundles in the outer integument; and a fibrous exotegmen (or its derived state). EmbryologicallyDrypeteae do not fit within thePhyllanthoideae and, as available nucleotide sequence data from therbcL gene suggest, are rather placed nearErythroxylaceae, Rhizophoraceae, Chrysobalanaceae, andLinaceae. Drypeteae share with those families a combination of the fibrous exotegmen, the endothelium, and the thick, multiplicative inner integument.     

Floral organogenesis of Helleborus thibetanus and Nigella damascena (Ranunculaceae) and its systematic significance

Floral organogenesis in Helleborus thibetanus and Nigella damascena was examined and compared using scanning electron microscopy and light microscopy, and the putative relationships of Helleborus and Nigella were analysed. H. thibetanus and N. damascena share some features of floral phyllotaxis and development of the sepals, petals, stamens and carpels, which are also found in other members of Ranunculaceae. However, they differ strongly in the number and degree of fusion of the carpels: in H. thibetanus, the two carpels are slightly united at the base, whereas, in N. damascena, the gynoecium is syncarpous and the five carpels are united throughout the ovary. Differences are also noted in petal development. The blade of the young petal of H. thibetanus develops two bulges which become connate and then fuse with the blade at the sides, developing more quickly than the blade and forming a tubular petal. In N. damascena, a single ridge is formed on the petal blade which develops into the smaller adaxial labium of the bilabiate petal, whereas the blade itself develops into the larger abaxial labium bearing two pseudonectaries. The outermost stamens are delayed in development in Helleborus, but not in Nigella. Although the results from our investigation are preliminary, differences in floral development characters suggest that Helleborus and Nigella may not be closely related and possibly support placement into separate tribes. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 166 , 431–443.     

Floral Morphology and Relationships of Clusia gundlachii with a Discussion of Floral Organ Identity and Diversity in the Genus Clusia

The genus Clusia L. is highly variable in many floral features. Several Clusia species have floral organs of mixed or uncertain identity, such as organs that are transitional between bracteoles and sepals, petaloid sepals, and partly petaloid stamen rings. Unique in Clusia is the "corona" of Clusia gundlachii Stahl, a thick, urn-shaped structure that is initiated as a ring primordium. In male flowers it surrounds a synandrium, and in female flowers it surrounds the ovary and a row of staminodes. The corona combines features typical of both petals and stamens of other Clusia species. It is hypothesized that this corona may be the result of the altered expression patterns of the genes that determine floral organ identity. Clusia gundlachii has many floral features in common with two small genera that are sometimes included in Clusia: Havetiopsis and Oedematopus. These genera have four thick connivent petals. Their apparent close relationship makes it seem likely that the corona of C. gundlachii evolved via congenital fusion of such petals. The corona is also somewhat similar to the staminodial rings present in many Clusia species, but taxa in which such organs occur show little similarity to C. gundlachii in terms of other floral characters.