Taxonomy of Eutetras (Compositae: Helenieae)

Abstract

Key, descriptions, synonymy, and range map are provided for the genus and its 2 species, E. palmeri and E. pringlei, of the central Mexican highlands. No new nomenclature is proposed. Eutetras, with two species, is one of several small genera endemic to the mountainous areas of south-central Mexico (Fig. 1). It was pro- posed by Gray in 1880 with the description of E. palmeri, Greenman adding the only other name, E. pringlei, in 1906. Rydberg (1914) treated Eutetras in the North American Flora, ac- cepting both species. He placed the genus in the tribe Helenieae, sub- tribe Amaurianae between the genera Amauria and Oxypappus. The only other genus included in the subtribe by Rydberg was Micro- spermum, but the latter appears to be more closely related to genera of the Galinsoginae (tribe Heliantheae) than it does to those of the Ama- urianae (Turner, unpubl.). In any case, except for Microspermum, Amaurianae are closely related to the subtribe Peritylanae and perhaps best merged with that taxon. Chromosome counts of n = 18 have been obtained for Eutetras pringlei, the only species examined to date (Turner and Johnston, 1961). EUTETRAS Gray, Proc. Am. Acad. 15: 39. 1880. Perennial herbs, growing in rock crevices in the manner of Perityle; leaves opposite, or rarely alternate along the upper-most stems; inflorescence a several- headed, corymbose cyme; heads conspicuous, radiate, both ray and disk flowers fertile; involucre campanulate, biseriate, the outer series linear, subherbaceous, the inner series similar to the outer but flat, dry, and with scarious margins; ray flowers white, the ligules 3-lobed; disk flowers yellow or white, 4-lobed, the corolla cylindric with a rather poorly developed throat; anthers 4, sagittate at the base; style branches linear, flattened, with marginal stigmatic lines, obtuse and hirtellous at the apex; achenes linear-oblong, 4-sided, the angles with pronounced