Female flowers and inflorescences of Didymelaceae

 In molecular analyses Didymelaceae together with Buxaceae form a fairly well-supported clade among families near the base of eudicots. Only little is known, however, about the flowers and inflorescences of Didymelaceae. In this study, the structure of the female flowers and inflorescences of Didymeles integrifolia was studied. Flowers are unicarpellate and orientation of the carpel is slightly deflected abaxially as in Proteaceae. Otherwise, Didymelaceae share many features of the gynoecium with Buxaceae and some other basal eudicots: the carpels are ascidiate in the lower half; anthetic carpels are completely closed by postgenital fusion; stigma is double-crested and widely decurrent; stigmatic papillae are unicellular and pear-shaped; the pollen tube transmitting tract is extensive and prominently differentiated; fruits are fleshy drupes with persistent stigma and style. However, the exceedingly elongate base of the integuments of Didymelaceae is an unusual feature among basal eudicots and even angiosperms. Received October 31, 2002; accepted December 17, 2002 Published online: March 31, 2003     

Inflorescence and floral morphology of Haptanthus hazlettii (Buxaceae,Buxales)

The enigmatic Central American tree Haptanthus hazlettii has recently been placed in Buxaceae (Buxales) by molecular evidence. However, Haptanthus appears morphologically to be fundamentally different from other Buxales in having pluriovular carpels with parietal placentation and reduced male reproductive units of an obscure morphological nature. The latter have been interpreted to be pairs of unistaminate flowers, or single flowers, either bearing two stamens or a pair of phyllomes with adnate introrse anthers. We (re‐)investigated the structure of the inflorescences and flowers of Haptanthus in order to clarify their homologies with reproductive structures of Buxales. We found that, despite some distinctive traits of flower morphology, Haptanthus shares many floral characters, including the opposite and pairwise arrangement of floral organs and the fusion between perianth members and stamens, with some Buxales and other early‐branching eudicots. The plicate and pluriovular gynoecium of Haptanthus may be the result of a drastic elongation of the symplicate zone, accompanied by an increase in ovule number, and is thus a derived trait in Buxales. The anther‐bearing structures are phyllomes with adnate anthers rather than stamens or unistaminate flowers. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 190–200.     

Anatomical studies on Sinofranchetia chinensis (Lardizabalaceae) and their systematic significance

The anatomical structures of the Chinese endemic and monotypic genus Sinofranchetia (Lardizabalaceae) are described. There are reticulate, simple-reticulate, scalariform, simple-scalariform and simple perforations in vessel elements as well as in the fibres in the secondary wood of the roots and the stems. The node is trilacunar. The vascular bundles in the petiole are arranged in a ring. Clustered crystals occur in the parenchymatous cells of stems, petioles and pedicles. Leaf stomata are actinocytic. The nodes of sepals, petals and stamens both in male and female flowers are unilacunar and one-traced. There are three sterile carpels with two to three traces in the male flowers, three fertile carpels with two to three traces, and sometimes three sterile carpels lacking a vascular supply. In morphology, the anther dehiscence mechanism and pollen in the female flowers are the same as in the male flowers, such that the so-called female flowers might be bisexual in morphology. In comparing morphology, the sex of the flowers and the perforations of the vessel elements in Sinofranchetia with Decaisnea and other genera of the Lardizabalaceae, Sinofranchetia is considered a basic group at least as the same evolutionary level in the family as Decaisnea . © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 271–281.     

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.     

The first record of gynodioecy in a species of Gnidia (Thymelaeaceae) from South Africa

Sexual polymorphism was studied in the shrub Gnidia wikstroemiana (Thunb.) Meisn. from the semiarid Nama Karoo Biome, South Africa. The populations comprised plants bearing either female flowers, or hermaphrodite flowers with variable female function. In two populations, female plants accounted for 36–37% of the flowering plants. Female flowers were smaller and their stamens were reduced to staminodes, but their styles were significantly longer than those of hermaphrodite flowers. Energy investment in flowers and fruits for females and hermaphrodites was measured using bomb calorimetry. Females produce a greater number of less costly flowers than hermaphrodites, and invest less energy per unit in production of flowers and inflorescences. In contrast, females invest more energy per unit in production of fruits and infructescences than hermaphrodites. Females overall invest 7.3% more energy in reproduction than hermaphrodites. Female flowers were obligate out-crossers (xenogamous), with 35% of nonmanipulated, open-pollinated flowers setting fruit, comparable with fruit set among selfed hermaphrodite flowers. The breeding strategy of G. wikstroemiana most closely resembles gynodioecy. This is the first report of sexual dimorphism in Gnidia L. and sub-Saharan Thymelaeaceae.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 219–233.     

Elucidating the unusual floral features of Swartzia dipetala (Fabaceae)

In this study, we evaluated the floral ontogeny of Swartzia dipetala, which has peculiar floral features compared with other legumes, such as an entire calyx in the floral bud, a corolla with one or two petals, a dimorphic and polyandrous androecium and a bicarpellate gynoecium. We provide new information on the function of pollen in both stamen morphs and whether both carpels of a flower are able to form fruit. Floral buds, flowers and fruits were processed for observation under light, scanning and transmission electron microscopy and for quantitative analyses. The entire calyx results from the initiation, elongation and fusion of three sepal primordia. A unique petal primordium (or rarely two) is produced on the adaxial side of a ring meristem, which is formed after the initiation of the calyx. The polyandrous and dimorphic androecium also originates from the activity of the ring meristem. It produces three larger stamen primordia on the abaxial side and numerous smaller stamen primordia on the adaxial side. These two types of stamens bear morphologically similar ripening pollen grains. However, prior to the dehiscence of thecae and presentation of pollen in the anther, only the pollen grains of the larger stamens contain amyloplasts. Two carpel primordia are initiated as distinct protuberances, alternating with the larger stamens, in a slightly inner position in the floral meristem, constituting the bicarpellate gynoecium. Both carpels are able to form fruit, although only one fruit is generally produced in a flower. The increase in gynoecium merism probably results in an increase in the surface deposition of pollen grains and consequently in the chance of pollination. This is the first study to thoroughly investigate organogenesis and the ability of the carpel to form fruit in a bicarpellate flower from a member of Fabaceae, in addition to the pollen ultrastructure in the heteromorphic stamens associated with the ‘division of labour’ sensu Darwin. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 303–320.     

POLLEN MORPHOLOGY AND THE RELATIONSHIPS OF SIMMONDSIA CHINENSIS TO THE ORDER EUPHORBIALES

Pollen from Simmondsia chinensis (Simmondsiaceae) was examined in LM, SEM, and TEM. The pollen is shed as monads, triangular in shape in polar view, with a 3-porate aperture type in which the pores are large and poorly defined. The tectum is irregularly scabrate, sometimes forming minute “islands” topped with spinules. In thin section, the endexine is thickened and lamellate in the aperture regions, and narrow in the mesoporus; the foot layer is well-defined but noticeably thicker in the mesoporus; and thin columellae support an essentially complete tectum. The pollen of four genera, Buxus, Pachysandra, Sarcococca, and Styloceras, from the Buxaceae to which Simmondsia has been assigned by some authors, was also examined and illustrated. The pollen morphology of two families frequently aligned with Simmondsiaceae, Euphorbiaceae and Pandaceae, is briefly discussed. For the most part pollen morphology supports the treatment of Simmondsia as a monotypic family, Simmondsiaceae.     

Intra‐individual variation of flowers in Gunnera subgenus Panke (Gunneraceae) and proposed apomorphies for Gunnerales

A study of inflorescence and flower development in 12 species from four of the six subgenera of Gunnera (Gunneraceae) was carried out. In the species of subgenus Panke, initiation of floral apices along the partial inflorescences is acropetal but ends up in the late formation of a terminal flower, forming a cyme at maturity. The terminal flower is the largest and the most complete in terms of merosity and number of whorls and thus it is the most diagnostic in terms of species‐level taxonomy. The lateral flowers undergo a basipetal gradient of organ reduction along the inflorescence, ranging from bisexual flowers (towards the distal region) to functionally (i.e. with staminodia) and structurally female flowers (towards the proximal region). Our results show that the terminal structure in Gunnera is a flower rather than a pseudanthium. The terminal flower is disymmetric, dimerous and bisexual, representing the common bauplan for Gunnera flowers. It has a differentiated perianth with two sepals and two alternate petals, the latter opposite the stamens and carpels. Comparisons with other members of the core eudicots with labile floral construction are addressed. We propose vegetative and floral putative synapomorphies for the sister‐group relationship between Gunneraceae and Myrothamnaceae. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 262–283.     

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.