61. Gamochaeta Wedd. (cudweed, everlasting)

Plants annual or biennial (perennial elsewhere), unbranched or few-branched from the base, fibrous-rooted or with slender taproots, not or only slightly aromatic when crushed or bruised. Stems erect or loosely to strongly ascending, sometimes ascending from a spreading base, moderately to densely pubescent with woolly hairs. Basal leaves sometimes present at flowering, not noticeably larger than the lower stem leaves. Stem leaves several to numerous, sessile, linear to oblanceolate or narrowly spatulate, rounded to bluntly or less commonly sharply pointed at the tip, mostly tapered at the base, the margins entire and sometimes finely wavy, the upper surface sparsely to densely woolly, sometimes appearing nearly glabrous, the undersurface densely white-woolly. Inflorescences narrow, often appearing as interrupted leafy spikes, with small clusters of heads axillary in the uppermost leaves and a short to somewhat elongate terminal spike, this sometimes reduced to a dense, conical or headlike mass in poorly developed plants, the individual heads sessile or minutely and inconspicuously stalked. Heads with the marginal florets pistillate, the central florets perfect. Involucre 3–5 mm long, narrowly ovoid to cup-shaped, the bracts in 3–5 overlapping series, mostly appressed, lanceolate to ovate or triangular, mostly sharply pointed at the tip, with dense, woolly hairs that obscure all or most of the involucre, ranging from white to more commonly straw-colored, usually brownish- and/or purplish- to pinkish-tinged, often slightly shiny. Receptacle flat, slightly convex, or concave, naked. Corollas 2.5–3.5 mm long, usually white, often purple at the tip. Pappus of numerous capillary bristles, these fused at the base and shed intact as a ring, minutely toothed. Fruits 0.4–0.7 mm long, narrowly oblong-obovoid, slightly flattened, the surface appearing pebbled or roughened with minute papillae, tan to yellowish brown, sometimes somewhat shiny. About 50 species, North America to South America, Caribbean Islands, introduced in the Old World.

Gamochaeta is one of the more easily recognizable segregates of Gnaphalium L. in temperate North America (although perhaps not elsewhere), even though no shared derived morphological character unique to the group has been identified to date. The name is accepted by many recent authors (Cabrera, 1961; Nesom, 1990a; Anderberg, 1991, 1994; Arriagada, 1998). The North American species of Gamochaeta have been studied intensively by Guy L. Nesom of the Botanical Research Institute of Texas in conjunction with his forthcoming treatment of the group for the Flora of North America Project. He has uncovered several morphologically cryptic taxa that formerly were included in G. purpurea and has done an excellent job of diagnosing these. The present treatment was improved following discussions with Dr. Nesom and his willingness to share unpublished data on the group. However, the three Missouri species remain very difficult to distinguish.