Biosystematics of Blennosperma (Compositae)

Abstract

Blennosperma is a taxonomically isolated genus of Helenieae (Compositae) with three distiinetive, allopatric species. Some of the biosystematic work on this genus has been presenited in a previous paper (Ornduff 1963). The present paper, which supplements the earlier one, emphasizes the systematics of the genus and discusses certaiil features of the ecology of the narrow endemic Blennospernca bakeri. Taxonomic Position of the Genus. Most taxonomists dealing with Blennospermsa have placed it in the tribe Helenieae of Compositae (Bentham 1873; Hoffmann 1889; Rydberg 1914; Keck 1959; Ferris 1960), although subtribal placement in the tribe has varied. Other authors have allied the genus with Senecioneae (DeCandolle 1838), Anthemideae (Remy 1849), and Heliantheae (Gray 1884). Many characters of the genus are somewhat anomalous in Helenieae. The monoecious heads have staminate disk florets and pistillate ray florets. In B. nanutr, there are apetalous pistillate florets intermixed with the petaliferous ray florets at the periphery of the heads. The highly modified styles of the staminate disk florets are undivided at maturity and serve mainly to eject the pollen mass by a pistoni effect during elongation (Fig. 6). The ligules of the ray florets are sessile on the ovaries. All florets are epappose. Some of these characters can be duplicated in a few genera of Helenieae, but many of them are rare or unknown in that tribe, and attest to the isolated and problematical taxonomic position of the genus. Its correct tribal placement awaits further study. A feature of unusual interest is that when the achenes of Blennosperma are moistened, numerous superficial papillae break open and emit pairs of tenuous filaments which imlbibe water, eventually swelling to form a thick colloidal mass over the surface of the achene. A similar phenomenon occurs in Crocidium, a genus usually placed in Senecioneae but also of douLbtful affinities (Ornduff et al. 1963).