A Survey of Mucilaginous Testa in Chamaesyce

Abstract

Seeds of Chamaesyce were studied for presence of mucilaginous testa. Samples were selected to represent all major systematic sections within the genus. Observations were made with a dissecting microscope following brief hydration of seeds; additional SEM observations of both intact and fractured dry seeds were made for selected species. With few exceptions, most of Boissier's subsections test positively fo r seed mucilage; however, mucilage is generally absent in subsections Gymnadeniae and "Sclerophyllae", for wich absence of mucilage is regarded as secondary loss from mucilagionus ancestors. Although mucilage production is associated with a well-defined subepidermal layer of macroesclereids, it is the surface layer of cells that actually secrete mucilage. Mucilage secreting cells and macroesclereids of mature testa are interpreted to develop from the epidermal layers of outer and inner integuments, respectively. Seed mucilages may play a role in seed hydration and/or seed dispersal.