Don Kaplan - his legacy: Influencing teaching and research
Jones, Cynthia S. .
Reconstructing leaf shape evolution in Pelargonium.
The flora of southern Africa is characterized by spectacular radiations. An example, Pelargonium L' Hér. (Geraniaceae), is the third largest plant genus in the Cape Floristic Region. This genus is best known as the source of horticulturally important "geraniums." The native species of Pelargonium are also notable for extraordinary diversity in growth form -- ranging from annuals to geophytes to stem succulents to woody shrubs. Even more remarkable is the diversity in leaf shape, ranging from entire to fully dissected to the midrib and ranging in length from 1 to greater than 45 cm. We examined leaf shape evolution within the genus using a recent phylogeny of 152 taxa produced by F. Bakker and colleagues (Taxon 53: 17). We scored over 125 species in terms leaf apex, base, outline shape, margin, and degree of dissection. We also classified patterns of major veins for 85 species into seven subcategories. The subcategories were combined into the broader categories of palmate, pinnate, and a form we called intermediate. Results to date indicate that leaves of ancestral species in Pelargonium had rounded apices, chordate bases, and ovate outlines. The ancestral venation pattern was palmate. A shift to predominately pinnate leaf venation accompanied shifts to the winter rainfall region and geophytic, stem succulent and caespitose subshrub growth forms. The degree of dissection of the lamina, described in five categories, resolved as "slightly lobed," suggesting subsequent selection has driven leaf shape in both directions, i.e. to highly dissected and to entire, and that current variation in the degree of lamina dissection most likely reflects recent, species specific adaptations within clades.
1 - University of Connecticut, Ecology & Evolutionary Biology, 75 North Eagleville Rd., Storrs, Connecticut, 06269-3043, USA
Presentation Type: Symposium
Location: Ballroom 2 (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 9:30 AM