| dc.description.abstract | The largest genus of the diverse angiosperm family Lythraceae, Cuphea, is remarkable in having floral hexamery associated with monosymmetry. Although some aspects of floral morphology in Cuphea have been investigated to date, we examined floral ontogeny in two species of this genus in comparison with Lythrum salicaria, a member of the same family with hexamerous polysymmetric flowers. Scanning electron microscopy was applied to observe both floral development and morphology. In all three species, calyx initiates first, then the primordia of the outer stamens appear more or less simultaneously with the gynoecium, then the inner stamens and the corolla is the last to initiate. In the apetalous C. ignea, we found no signs of petal initiation. Flowers of L. salicaria can be either hexa- or pentamerous, sometimes with irregular merism, and they are less stable than those of Cuphea spp. in this respect. We classified two features of monosymmetry in Cuphea as ‘early’, viz. absence of initiation of the dorsalmost outer stamen and asynchronous initiation of carpels. The other features of floral monosymmetry in Cuphea appear later, these are unequal development of carpels, the adaxial position of disc, the monosymmetric placenta, and the unequal level of staminal insertion as well as the distribution of indumentum. The presence of (putative) secretory stomata on the disc confirms the hypothesis of its role as nectary. Our results evidence for the non-phyllome origin of the epicalyx in Lythraceae. | sr |
