Seed ontogeny in Eupatorieae: development and functional aspects

Abstract

Changes in the role of the seed coat during seed development have not been extensively examined, mainly because the greater emphasis is usually placed upon its function in the mature seed. Additionally, there have been few studies on the seeds of Asteraceae, and those that have been undertaken rarely addressed functional aspects of seeds. The present study examined seed ontogeny in species of Eupatorieae (Asteraceae) and investigated the role of the seed coat in seed nutrition and abortion. A new pattern of seed vasculature was encountered for the family, in addition to two other types previously described for other species. The most significant role of the seed coat among the species of Eupatorieae examined was in seed nutrition. The inner mesotesta is consumed during seed development, while the remaining layers collapse at maturity and cease to function. Seed abortion was observed in all of the species examined, varying from 95% in Symphyopappus reticulatus to 18.5% in Vittetia orbiculata. Changes in endothelial tissue were found in all episodes of abortion, although variation was observed concerning remnant structures and their degree of development. The young seed coat in Asteraceae has a nutritive role, while at maturation the pericarp serves a protective function.