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

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