Systematics Section / ASPT
Karst, Lisa , Wilson, Carol A. .
Pollinator shift and corresponding radiation in Sisyrinchium subgenus Sisyrinchium (Iridaceae).
Sisyrinchium is a large New World genus of approximately 150 species. Analyses of the cpDNA matK and flanking introns of the trnK and the nrDNA ITS region for 30 Sisyrinchium and outgroups resulted in trees with strong basal support using either parsimony or maximum likelihood methods. These analyses revealed three subgeneric groups and several radiations, one of which corresponds with a shift from a specialized pollinator to a generalized pollination system. Most species from subgenus Echthronema resolved into a monophyletic basal group. These species possess floral morphology of yellow unmarked tepals, an aglandular partially fused filament column, long anthers and spreading style branches. The remaining members of subgenus Echthronema form a second monophyletic group. These possess floral morphology of yellow tepals with distinct cupping and striped or spotted throat. They also possess a partially fused filament column with a distinct collar of oil bearing glands (eliaophores) which are attractive to euglossine bees. Anthers are shorter relative to flower size, and style branches are curved outward rather than spreading. Additionally, some species have a swollen area at the base of the filament tube, similar to members of its putative sister genus Olsynium. In Olsynium this structure functions as a nectary, which is not known in any Sisyrinchium. Members of subgenus Sisyrinchium form a monophyletic group and also possess glands, although these glands are restricted to the filament tube or found diffusely throughout the floral structures; tepals, ovary, and pedicel. Flowers of this clade have a fully fused filament tube, and short stigma lobes. Internally, there is a polytomy not resolved by ITS and matK data sets which may represent a geographically widespread radiation corresponding to loss of their relationship with a specialized pollinator. This shift would have facilitated their radiation into temperate North America, where euglossine bees do not occur.
1 - Portland State University, Biology Department, POB 751, Portland, Oregon, 97207-0751, USA
Presentation Type: Paper
Location: Cottonwood B (Snowbird Center)
Date: Monday, August 2nd, 2004
Time: 1:45 PM