Heterospermy analysis in Rhododendron luteum Sweet and Rhododendron schlippenbachii Maxim. (Ericaceae)

Abstract

Seed propagation is one of the main methods of rhododendron planting stock. Obtaining of the seeds from introduced plants (native reproduction) is very important for successful introduction. In Rhododenron schlippenbachii and R. luteum the structural features of the ovule before pollination, the development of the embryo, endosperm, and seed coat are studied. The studied species are characterized by heterospermy. Mature seeds differ in shape, size, internal structure, and vitality. Seeds in ripe fruits can be divided into 3 fractions. Large seeds often contain an embryo, an endosperm with an endosperm cavity, and later usually germinate. In the seeds of the middle fraction, the endosperm is usually not fully formed, and the embryo may be absent. Small seeds are mainly represented by preserved integument and chalaza cells with thickened cell walls, without signs of the development of embryonic structures. Seeds of medium and, especially, small fractions of R. luteum often lack a wing border, which is present in large seeds of this species. In them, as well as in some of the seeds of the large fraction of both species, secretory cells are formed in the base of funicular region of raphe, which, possibly, perform the function of elaiosomes.