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Published In: Chloris Andina 1(4–6): 151. 1855[1856]. (15 Dec 1856) (Chlor. Andina) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/26/2009)
Acceptance : Accepted
Project Data     (Last Modified On 8/14/2009)

 

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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.

 

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1 1. Receptacle becoming deeply concave (cuplike) at fruiting; leaves (except sometimes the upper ones) appearing only slightly to moderately bicolorous, the upper surface moderately to densely woolly but still appearing somewhat darker or greener than the undersurface ... 2. G. PENSYLVANICA

Gamochaeta pensylvanica
2 1. Receptacle becoming flat to slightly concave at fruiting; leaves appearing strongly bicolorous, the upper surface sparsely woolly or with patches of cobwebby hairs, often appearing nearly glabrous

3 2. Hairs not swollen at the base; involucre 3.03.5 mm long ... 1. G. ARGYRINEA

Gamochaeta argyrinea
4 2. Most or all of the foliar hairs (most easily observed on the more sparsely pubescent upper surface) with a minute, swollen or expanded basal cell (requires magnification to observe); involucre 4.04.5 mm long ... 3. G. PURPUREA Gamochaeta purpurea
 
 
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