Evolution and Development of Floral Diversity in Streptocarpus and Saintpaulia

• Published in: Annals of botany Vol. 84; no. 1; pp. 49 - 60
• Main Authors: HARRISON, C.JILL, MÖLLER, MICHAEL, CRONK, QUENTIN C.B.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Science Ltd 01.07.1999; Oxford University Press; Academic Press Limited; Oxford Publishing Limited (England)
• Subjects: African Violet; African Violet, Cape Primrose, CYCLOIDEA , floral development, floral diversity, enantiostyly, Gesneriaceae, inflorescence architecture, Saintpaulia, Streptocarpus , sympetaly; Anthers; calyx; Cape Primrose; Corolla; cultivars; CYCLOIDEA; enantiostyly; Evolution; floral development; floral diversity; Flowering; Flowers; Gesneriaceae; gynoecium; inflorescence architecture; Inflorescences; Meristems; nucleotide sequences; ovules; Petals; phylogeny; plant morphology; Pollen; Pollination; quantitative analysis; ribosomal DNA; Saintpaulia; Saintpaulia ionantha; size; Streptocarpus; sympetaly; traits; African Violet, Cape Primrose, CYCLOIDEA , floral development, floral diversity, enantiostyly, Gesneriaceae, inflorescence architecture, Saintpaulia, Streptocarpus , sympetaly
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1006/anbo.1999.0887

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 inStreptocarpus 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 withinStreptocarpus/Saintpaulia. The most extreme difference is between Saintpaulia ionantha and aSaintpaulia 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.