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.