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.     

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.     

耧斗菜属花部形态发生

用扫描电镜观察了无距耧斗菜（Ａｑｕｉｌｅｇｉａ ｅｃａｌｃａｒａｔａ Ｍａｘｉｍ ．）和北美耧斗菜（Ａ． ｃａｅｒｕｌｅａＪａｍ ｅｓ．）雄蕊群和雌蕊群的发生过程,并在光学显微镜下检查了同一雄蕊群不同轮雄蕊小孢子发育的顺序． 发现耧斗菜属雄蕊群的发生是向心发生,而小孢子发育和花药成熟顺序是离心的． 说明该属雄蕊群离心发育是次生现象;它在不同类群中出现,可能具有平行演化的性质,其系统学价值尚需重新评价     

Profile of a flower: How rates of morphological evolution drive floral diversification in Ericales and angiosperms

Premise

Recent studies of floral disparity in the asterid order Ericales have shown that flowers vary strongly among families and that disparity is unequally distributed between the three flower modules (perianth, androecium, gynoecium). However, it remains unknown whether these patterns are driven by heterogeneous rates of morphological evolution or other factors.

Methods

Here, we compiled a data set of 33 floral characters scored for 414 species of Ericales sampled from 346 genera and all 22 families. We conducted ancestral state reconstructions using an equal-rates Markov model for each character. We estimated rates of morphological evolution for Ericales and for a separate angiosperm-wide data set of 19 characters and 792 species, creating “rate profiles” for Ericales, angiosperms, and major angiosperm subclades. We compared morphological rates among flower modules within each data set separately and between data sets, and we compared rates among angiosperm subclades using the angiosperm data set.

Results

The androecium exhibits the highest evolutionary rates across most characters, whereas most perianth and gynoecium characters evolve more slowly in both Ericales and angiosperms. Both high and low rates of morphological evolution can result in high floral disparity in Ericales. Analyses of an angiosperm-wide floral data set reveal that this pattern appears to be conserved across most major angiosperm clades.

Conclusions

Elevated rates of morphological evolution in the androecium of Ericales may explain the higher disparity reported for this floral module. Comparing rates of morphological evolution through rate profiles proves to be a powerful tool in understanding floral evolution.     

The ontogenetic basis for floral diversity in <Emphasis Type="Italic">Agonis</Emphasis>, <Emphasis Type="Italic">Leptospermum</Emphasis> and <Emphasis Type="Italic">Kunzea</Emphasis> (Myrtaceae)

Floral development in three species each of Leptospermum and Kunzea, and one species of Agonis, is described and compared. Differences in the number of stamens and their arrangement in the flower at anthesis are determined by the growth dynamics of the bud. In Leptospermum, early expansion of the bud is predominantly in the axial direction and causes the stamen primordia to be initiated in antepetalous chevrons. In Kunzea, early expansion occurs predominantly in the lateral direction and successive iterations of stamen primordia are inserted alternately at more or less the same level. In both genera, further expansion in the lateral plane spreads the stamens into a ring around the hypanthium. Agonis flexuosa is similar to Leptospermum. Other variable factors include the timing at which stamen initiation commences (earlier in Leptospermum than Kunzea), the duration of stamen initiation (hence the total number of stamens produced – varies within genera), and very late differential expansion that forces stamens into secondary antesepalous groups in A. flexuosa and L. myrsinoides.The authors thank Dr H. Toelken for kindly providing some material and the impetus for this project. This research was supported by Australian Research Council grant AS19131815.     

The discovery of polyandry in Curculigo (Hypoxidaceae): implications for androecium evolution of asparagoid monocotyledons

BACKGROUND AND AIMS: Individual flowers of the monocot Curculigo racemosa (Hypoxidaceae, Asparagales) are regularly polyandrous. To evaluate the significance of this almost unique character among Asparagales for flower evolution of asparagoid monocots, flowers of C. racemosa were studied comparatively. METHODS: Anthetic flowers as well as early floral developmental stages were studied by light and scanning electron microscopy. KEY RESULTS: Despite the polyandry, floral development is similar to that of other Asparagales with a developmental gradient from adaxial to abaxial. Stamens initiate simultaneously and the diameter of staminal primordia is about half of that in species with six anthers. The number of stamens is not fixed (12-26) and varies within the same inflorescence. Surprisingly, the gynoecium can be four- or six-locular, besides the normal trimerous state. CONCLUSIONS: The discovery of a polyandrous Curculigo reveals plasticity of stamen number at the base of Asparagales. Orchidaceae - sister to all other Asparagales - has a reduced stamen number (three, two or one), whereas in Hypoxidaceae - part of the next diverging clade - either the normal monocot stamen number (six), polyandry (this study) or the loss of three anthers (Pauridia) occurs. However, at present it is impossible to decide whether the flexibility in stamen number is autapomorphic for each group or whether it is a synapomorphy. The small size of stamen primordia of Curculigo is conspicuous. It allows more space for additional androecial primordia. Stamens are initiated as independent organs, and filaments are not in bundles, hence C. racemosa is not secondarily polyandrous as may be the case in the distantly related Gethyllis of asparagoid Amaryllidaceae. The increase in carpel number is a rare phenomenon in angiosperms. A possible explanation for the polyandry of C. racemosa is that it is a natural SUPERMAN-deficient mutant, which shows an increase of stamens, or ULTRAPETALA or CARPEL FACTORY mutants, which are polyandrous and changed in carpel number.     

Evolution of perianth and stamen characteristics with respect to floral symmetry in Ranunculales

BACKGROUND AND AIMS: Floral symmetry presents two main states in angiosperms, namely polysymmetry and monosymmetry. Monosymmetry is thought to have evolved several times independently from polysymmetry, possibly in co-adaptation with specialized pollinators. Monosymmetry commonly refers to the perianth, even though associated androecium modifications have been reported. The evolution of perianth symmetry is examined with respect to traits of flower architecture in the Ranunculales, the sister group to all other eudicots, which present a large diversity of floral forms. METHODS: Characters considered were perianth merism, calyx, corolla and androecium symmetry, number of stamens and spurs. Character evolution was optimized on a composite phylogenetic tree of Ranunculales using maximum parsimony. KEY RESULTS: The ancestral state for merism could not be inferred because the basalmost Eupteleaceae lack a perianth and have a variable number of stamens. The Papaveraceae are dimerous, and the five other families share a common trimerous ancestor. Shifts from trimery to dimery (or reverse) are observed. Pentamery evolved in Ranunculaceae. Ranunculales except Eupteleaceae, present a polysymmetric ancestral state. Monosymmetry evolved once within Papaveraceae, Ranunculaceae and Menispermaceae (female flowers only). Oligandry is the ancestral state for all Ranunculales, and polyandry evolved several times independently, in Papaveraceae, Menispermaceae, Berberidaceae and Ranunculaceae, with two reversions to oligandry in the latter. The ancestral state for androecium symmetry is ambiguous for the Ranunculales, while polysymmetry evolved immediately after the divergence of Eupteleaceae. A disymmetric androecium evolved in Papaveraceae. The ancestral state for spurs is none. Multiple spurs evolved in Papaveraceae, Berberidaceae and Ranunculaceae, and single spurs occur in Papaveraceae and Ranunculaceae. CONCLUSIONS: The evolution of symmetry appears disconnected from changes in merism and stamen number, although monosymmetry never evolved in the context of an open ground plan. In bisexual species, monosymmetry evolved coincidently with single spurs, allowing us to propose an evolutionary scenario for Papaveraceae.     

Comparative floral structure and systematics in Cucurbitales (Corynocarpaceae, Coriariaceae, Tetramelaceae, Datiscaceae, Begoniaceae, Cucurbitaceae, Anisophylleaceae)

Floral structure, including morphology, anatomy and histology, was comparatively studied in representatives of all seven families of Cucurbitales as currently circumscribed by other authors based on molecular analyses and including Corynocarpaceae, Coriariaceae, Tetramelaceae, Datiscaceae, Begoniaceae, Cucurbitaceae and Anisophylleaceae. Three superfamilial clades are supported by floral structure: Tetramelaceae/Datiscaceae, Tetramelaceae/Datiscaceae/Begoniaceae and Corynocarpaceae/Coriariaceae. Anisophylleaceae appear most isolated in Cucurbitales, and show more similarities with Oxalidales, especially Cunoniaceae, although some features of interest are shared with other Cucurbitales and not Oxalidales. Tetramelaceae and Datiscaceae share dioecy, completely isomerous (but not regularly pentamerous) flowers (not in male Datiscaceae), only small sepals, lacking petals (not in male Octomeles). Tetramelaceae, Datiscaceae and Begoniaceae share the presence of numerous small ovules and seeds with a large‐celled surface, 2‐cell‐layered integuments, and a collar around the funicle by an extension of the outer integument. Corynocarpaceae and Coriariaceae share thick petals, unifacial stigmas, superior ovaries with a single, median, pendant syntropous ovule per carpel, and annular outer integuments with vasculature at the base. The four classical core families of Cucurbitales: Tetramelaceae, Datiscaceae, Begoniaceae and Cucurbitaceae (relationship unresolved, not retrieved as a clade as yet in molecular studies) share in various combinations androdioecy, basifixed and extrorse or latrorse anthers, trimerous gynoecia, bifurcate free carpel parts, an extended roof over the ovary formed by the ventral parts of the carpels, and parietal placentae. Trends of interest at the order level are unisexual flowers, thick, pointed petals (if present) that do not conform to the model in other rosids or basal core eudicots, a 2‐cell‐layered inner integument, which is delayed in development, and lacking or scant tanniferous tissues in flowers. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 145 , 129–185.     

Floral Morphogenesis of Aquilegia L. (Ranunculaceae)

The androecial and gynoecial initiation in Aquilegia ecalcarata Maxim. and A. caerulea James. were observed under scanning electron microscope (SEM). Also the microspore developmental sequence of different whorls of stamens in the same androecium was examined under the light microscope (LM). It was shown that the androecial initiation was centripetal, whereas the microsporogenesis and anther maturation were centrifugal. Thus, the centrifugal development of androecium in this genus was a secondary phenomenon. The authors considered that as has been reported centrifugal development of androecium appeared in different groups could be parallel to centripetal development in the course of evolution, of which the phylogenetic significance merits further approach.