Ontogenetic Anatomy of Streptocarpus grandis(Gesneriaceae) with Implications for Evolution of Monophylly

The monophylly of Streptocarpus grandis was examined ontogeneticallyand anatomically. When the seed is shed, the embryo is composedof a hypocotyl and two equal-sized cotyledons, lacking rootand shoot apices. During germination, cell division and subsequentcell enlargement occur in the hypocotyl and cotyledons. Thehypocotyl soon produces a primary root from its distal tip;this involves surface and subsurface cells at the point of attachmentof the suspensor remnant. In the cotyledons, cell enlargementand differentiation occur basipetally, leaving small meristematiccells at the bases. These small cells give rise to the basalmeristem in one of the two cotyledons, which contributes toan accrescent cotyledon. The groove meristem, which later differentiatesinto an inflorescence, arises in place of shoot apices whenthe cotyledons become visibly unequal in size. It later exhibitsa tunica-corpus like configuration and differentiates directlyinto an inflorescence meristem. The evolution of this uniquegrowth of one-leaved Streptocarpus is discussed with regardto morphogenetic data.Copyright 2000 Annals of Botany Company Anisocotyly, developmental anatomy, evolution, Gesneriaceae, one-leaf plant, ontogeny, Streptocarpus grandis