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.