A survey of our own comparative studies on several larger clades of rosids and over 1400 original publications on rosid flowers shows that floral structural features support to various degrees the supraordinal relationships in rosids proposed by molecular phylogenetic studies. However, as many apparent relationships are not yet well resolved, the structural support also remains tentative. Some of the features that turned out to be of interest in the present study had not previously been considered in earlier supraordinal studies. The strongest floral structural support is for malvids (Brassicales, Malvales, Sapindales), which reflects the strong support of phylogenetic analyses. Somewhat less structurally supported are the COM (Celastrales, Oxalidales, Malpighiales) and the nitrogen-fixing (Cucurbitales, Fagales, Fabales, Rosales) clades of fabids, which are both also only weakly supported in phylogenetic analyses. The sister pairs, Cucurbitales plus Fagales, and Malvales plus Sapindales, are structurally only weakly supported, and for the entire fabids there is no clear support by the present floral structural data. However, an additional grouping, the COM clade plus malvids, shares some interesting features but does not appear as a clade in phylogenetic analyses. Thus it appears that the deepest split within eurosids–that between fabids and malvids - in molecular phylogenetic analyses (however weakly supported) is not matched by the present structural data. Features of ovules including thickness of integuments, thickness of nucellus, and degree of ovular curvature, appear to be especially interesting for higher level relationships and should be further explored. Although features of interest are not necessarily stable at the level of a large clade, they do show a considerable concentration in particular clades and are rare or lacking in others. This may be viewed as a special trend for this feature to evolve in this group or to be conserved as a synapomorphy (or a combination of both).

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First steps towards a floral structural characterization of the major rosid subclades

Floral monosymmetry and asymmetry are traced through the angiosperm orders and families. Both are diverse and widespread in angiosperms. The systematic distribution of the different forms of monosymmetry and asymmetry indicates that both evolved numerous times. Elaborate forms occur in highly synorganized flowers. Less elaborate forms occur by curvature of organs and by simplicity with minimal organ numbers. Elaborate forms of asymmetry evolved from elaborate monosymmetry. Less elaborate form come about by curvature or torsion of organs, by imbricate aestivation of perianth organs, or also by simplicity. Floral monosymmetry appears to be a key innovation in some groups (e.g., Orchidaceae, Fabaceae, Lamiales), but not in others. Floral asymmetry appears as a key innovation in Phaseoleae (Fabaceae). Simple patterns of monosymmetry appear easily “reverted” to polysymmetry, whereas elaborate monosymmetry is difficult to lose without disruption of floral function (e.g., Orchidaceae). Monosymmetry and asymmetry can be expressed at different stages of floral (and fruit) development and may be transient in some taxa. The two symmetries are most common in bee-pollinated flowers, and appear to be especially prone to develop in some specialized biological situations: monosymmetry, e.g., with buzz-pollinated flowers or with oil flowers, and asymmetry also with buzz-pollinated flowers, both based on the particular collection mechanisms by the pollinating bees. Floral monosymmetry has developed into a model trait in evo-devo studies, whereas floral asymmetry to date has not been tackled in molecular genetic studies.

/pdf/the-immense-diversity-of-floral-monosymmetry-and-asymmetry-58g5dund00.pdf

The Immense Diversity of Floral Monosymmetry and Asymmetry Across Angiosperms

Floral Structure of Kirkia (Kirkiaceae) and its Position in Sapindales

Gynoecium structure in Sapindales and a case study of Trichilia pallens (Meliaceae)

The floral anatomy ofSwietenia mahogoni Jacq.,Soymida febrifuga Juss.,Chukrassia valutino A. Juss.,Dysoxylum binectariferum Hook.,Aphanamixis rohituka W. & A. andHeynea trijuga Roxb. are discussed. Calyx is supplied by two whorls of traces inSwietenia, Aphanamixis, Chukrassia andHeynea and only one whorl of traces inSoymida andDysoxylum. In all the species, exceptHeynea, petals receive their supply independently. InHeynea petals receive their supply from compound strands. Staminal tube receives its supply from compound strands inSwietenia,Chukrassia, Heynea, Aphanamixis and from independent strands inSoymida andDysoxylum. Anthers are syngenesious inDysoxylum.

Sushma Gupta

Papers

Morphological studies in Meliaceae. II. A reinvestigation of floral anatomy of members of Swietenieae and Trichilieae