Cephaelis sphaerocephala Rob., Proc. Am. Acad. 45: 408. 1910.
Rudgea inurbana Standl., Field Mus. Publ. Bot. 8: 234. 1930.
The stipules of this species are palmately lacerate with 8-11 linear-aristate to lanceolate segments 2-3 mm long and densely buff-ciliate, giving a Rudgea-like appearance. In Prance et al 5441 the stipules, however, are mainly entire or bifid. In habit the plant varies from a creeping herb (Prance et al 5441) to a subshrub to 1 meter tall. The numerous flowers (30-35) are crowded into a head and are sessile and provided with dense, yellow-brown hairs all around their bases and between the flowers. They are not subtended individually by special bracts or bracteoles, but are surrounded by the 8-13 outer bracts of unequal lengths which comprise the involucre.
Müller-Argoviensis placed this species in his series E. Ipecacuanhales, in which the bracts and bracteoles of the flowers are obsolete or rudimentary. He placed species of similar appearance with pubescent stems and monocephalous inflorescences in series F. Trichocephaleae, characterized by him as having the bracts and bracteoles of the flowers developed or more conspicuous, this series including P. medusula, P. trichophora, P. trichophoroides, P. horridula, and P. japurensis. As has been indicated above elsewhere, no rigid pattern appears evident to circumscribe the various species treated above within different sections or series or genera.