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 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.     

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.     

Melting pot of biodiversity: first insights into the evolutionary patterns of the Colchic bramble flora (Rubus subgenus Rubus,Rosaceae)

The Caucasus is a biodiversity hotspot of global significance, containing a number of highly diverse and species‐rich plant taxa. The region is also thought to be an important evolutionary hotspot for Rubus subgenus Rubus (brambles). However, Caucasian brambles have only been poorly studied to date and our knowledge of their evolutionary mechanisms, systematics and taxonomic variability remains rudimentary. Therefore, the objectives of this study were to shed light on the evolution, diversity and reproduction modes of Rubus in one of the two Caucasian glacial refugia, Colchis. Flow cytometry measurements were used to estimate DNA ploidy, a flow cytometric seed screen was conducted to determine reproduction mode and Sanger sequencing of two non‐coding plastid regions was used to reveal phylogenetic patterns. The most common ploidy level was tetraploid, followed by diploid and (rarely) triploid. Intra‐individual variation in reproduction mode was low, as the morphoseries Glandulosi and Radula exhibited strict sexuality and other taxa were mostly apomictic. A few exceptions were observed that deserve further attention, e.g. sexuality induced hypothetically by haploid pollen or by environmental conditions, a high proportion of triploid embryos or polyspermy. Plastid haplotype variability revealed specific, ancient evolutionary patterns with limited involvement of extant diploid taxa and recent isolation from European brambles. We provide the first insight into the variability and evolution of Colchic brambles, which serves as a starting point for further systematic and evolutionary studies.     

Angiosperm phylogeny inferred from sequences of four mitochondrial genes

An angiosperm phylogeny was reconstructed in a maximum likelihood analysis of sequences of four mitochondrial genes, atpl, matR, had5, and rps3, from 380 species that represent 376 genera and 296 families of seed plants. It is largely congruent with the phylogeny of angiosperms reconstructed from chloroplast genes atpB, matK, and rbcL, and nuclear 18S rDNA. The basalmost lineage consists of Amborella and Nymphaeales (including Hydatellaceae). Austrobaileyales follow this clade and are sister to the mesangiosperms, which include Chloranthaceae, Ceratophyllum, magnoliids, monocots, and eudicots. With the exception of Chloranthaceae being sister to Ceratophyllum, relationships among these five lineages are not well supported. In eudicots, Ranunculales, Sabiales, Proteales, Trochodendrales, Buxales, Gunnerales, Saxifragales, Vitales, Berberidopsidales, and Dilleniales form a basal grade of lines that diverged before the diversification of rosids and asterids. Within rosids, the COM (Celastrales-Oxalidales-Malpighiales) clade is sister to malvids (or rosid Ⅱ), instead of to the nitrogen-fixing clade as found in all previous large-scale molecular analyses of angiosperms. Santalales and Caryophyllales are members of an expanded asterid clade. This study shows that the mitochondrial genes are informative markers for resolving relationships among genera, families, or higher rank taxa across angiosperms. The low substitution rates and low homoplasy levels of the mitochondrial genes relative to the chloroplast genes, as found in this study, make them particularly useful for reconstructing ancient phylogenetic relationships. A mitochondrial gene-based angiosperm phylogeny provides an independent and essential reference for comparison with hypotheses of angiosperm phylogeny based on chloroplast genes, nuclear genes, and non-molecular data to reconstruct the underlying organismal phylogeny.     

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.     

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.     

Evolution of reproductive traits in the mahagony family (Meliaceae)

Meliaceae are a mostly pantropical family in the Sapindales, bearing flowers typically provided with a staminal tube, formed by filaments that are fused partially or totally. Nevertheless, several genera of subfamily Cedreloideae have free stamens, which may be adnate to an androgynophore in some taxa. The fact that the family exhibits a wide diversity of floral and fruit features, as well as of sexual systems and pollination syndromes, presents interesting questions on the evolutionary processes that might have taken place during its history. In this study, we analyzed the distribution of 20 reproductive morphological traits of Meliaceae, upon an available molecular phylogenetic framework, using 31 terminals from the family's two main clades (Cedreloideae and Melioideae), plus six Simaroubaceae taxa as outgroup. We aimed to identify and/or confirm synapomorphies for clades within the family and to develop hypotheses on floral evolution and sexual systems in the group. Our reconstruction suggests that the ancestor of Meliaceae was possibly provided with united stamens and unisexual flowers in dioecious individuals, with a subsequent change to free stamens and monoecy in the ancestor of Cedreloideae. Most characters studied show some degree of homoplasy, but some are unique synapomorphies of clades, such as the haplostemonous androecium. An androgynophore defines the Cedrela‐Toona clade. The comparative approach of our study and the evolutionary hypotheses generated herein reveal several aspects demanding further structural investigation, and possible evolutionary pathways of the reproductive structures along with the lineages' diversification, mostly related to the specialization of sexual systems, floral biology, and dispersal strategies.     

Reproductive structures and phylogenetic framework of the rosids - progress and prospects

With ca 70.000 species the rosids contain more than a quarter of the total angiosperm species diversity. This taxonomic richness is reflected in a tremendous variety of floral organization and architecture. Rosids have received extensive molecular phylogenetic study. As a result, the monophyly and taxonomic composition of the group are well established. In addition, many subclades at the order level are now apparent. Deeper relationships, however, are still largely equivocal. As in many other parts of the plant tree of life, it will be impossible to reach an adequate understanding of the evolutionary history of the rosids without taking into account information from comparative morphological studies of extant and, in particular, also of fossil taxa. The fossil record of rosids is rich in well-preserved reproductive structures, and together with recent results from comparative studies of extant rosids, provides a wealth of floral structural data. Although much remains to be done at all levels, fresh attempts to synthesize and possibly reconcile results from molecular phylogenetics, comparative floral morphology, and palaeobotany, seem timely.