Taxonomy of Pericome (Compositae-Peritylinae)

Abstract

The taxonomy of Pericome (Compositae) is reviewed in connection with recent systematic studies of the subtribe Peritylinae. Included are distributional notes, descriptions, and a key to the two species, P. caudata and P. macrocephala. Two species are recognized for the genus Pericome. Pericome caudata A. Gray is widespread and common in Upper Sonoran to Montane Zones of the southwestern United States, and is also known from Chihuahua, Mexico. The second taxon, P. macrocephala Rob., is known only from its type locality in Durango, Mexico. Rydberg (N. Amer. Fl., 34: 11-29, 1914) placed Pericome in the subtribe Peritylinae (Helenieae). My recent studies of the subtribe have substantiated this disposition, and have suggested that Pericome is closely related to Perityle Benth. (Powell, Sida, 3: 270-278, 1968). This generic affinity is evident in general vegetative and floral morphology, but is particularly expressed through similarities in achene and pappus structure. Pericome is best distinguished from Perityle by its shrubby habit, capitulescence of densely aggregated heads, and coalescent involucral bracts. Pericome plants are the largest of the subtribe, with some reaching a height of nearly 2 m and spreading up to a width of 2 m. PERICOME A. Gray, P1. Wright. 2:81. 1853. Plants subshrubby or herbaceous perennials, 1 m or more high, many-stemmed from the base and spreading, the stems copiously leaved, many-branched especially above, subterete, striate, sparsely puberulent to nearly glabrous except apical branches often densely puberulent to tomentulose; leaves mostly opposite, 5-16 cm long including the petiole, 2-10 cm wide, progressively smaller upwards, blades typically deltoidhastate and long-attenuate (caudate) apically, or less often subhastate, ovate, or cordate and longto short-attenuate, 3-5 lobed, cleft, or 1 Supported by NSF Grants GB-7740 and GB-20361.