Floral diversity in Streptocarpus and Saintpaulia can be classified into six distinct types on the basis of quantitative variation. Species are differentiated by overall flower size and by corolla lobe size in relation to corolla tube opening size, characteristics implicated in pollination ecology. Saintpaulia has a very short corolla tube and yellow protruding anthers, strikingly different from Streptocarpus , and probably associated with buzz pollination. Some species of Streptocarpus and all species of Saintpaulia are enantiostylous, a feature often linked to buzz pollination. Mapping of these floral characters onto a molecular phylogeny based on ITS sequence data showed that in Streptocarpus flower size evolved from small to large, with reversals in four species. The putatively bee pollinated ‘open-tubed’ type had two independent origins, and the putatively lepidopteran-pollinated ‘keyhole’ type had four separate origins. Enantiostyly had one or two origins. The degree of zygomorphy varies within Streptocarpus/Saintpaulia. The most extreme difference is between Saintpaulia ionantha and a Saintpaulia peloric cultivar. The developmental basis of floral variation was compared using SEM in three very different types: Streptocarpus primulifolius, Saintpaulia ionantha and a Saintpaulia peloric cultivar. Differences in corolla tube length and zygomorphy are established very early in flower development. Small, early changes in flower development establish major changes in mature floral morphology.
Evolution and Development of Floral Diversity in Streptocarpus and Saintpaulia
Publication: Annals of Botany
Genera: Saintpaulia, Streptocarpus