XVI International Botanical Congess

One of the apomorphies characterizing the core Malvales (Bombacaceae, Malvaceae, Sterculiaceae, Tiliaceae) is the possession of trichomatous floral nectaries (N), a type absent in the relatives of this group, where other kinds of N occur, or none at all. Malvalean floral N consist of multicellular hairs usually aggregated in cushions. They presumably have evolved from hydathodes, i.e. dispersed trichomes active in the bud stage and ubiquitous in the green parts. The extrafloral N, likewise trichomatous, show various steps of hair aggregation, which may reflect the evolutionary pathway whereby such aggregates became established in the flower. The mostly calyx-borne position of the N has strongly influenced flower construction. Different modes of nectar exposition and the repeated occurrence of taxa with nectarless deceptive or pollen flowers are discussed relative to new concepts of classification suggested by molecular data.