The segregate genera of Gnaphalium (Asteraceae)
The genus Gnaphalium, colloquially referred to as cudweeds, has been found to be highly polyphetic (Andeberg 1991). The traditional classification, of a broad and variable Gnaphalium, includes species of very different lineages, and hence is artificial (i.e., it does not accurately portray the evolutionary history of the group). The genus has, therefore, been dismantled and reorganized into smaller, more homogenous, and monophyletic groups. Nesom (1990a, 1990b) has provided detailed discussion of morphological distinctions and rationale for recognition of multiple genera of cudweeds.
Key to the segregate genera of Gnaphalium in New England
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1a. Phyllaries yellow-white to sordid white; capitulescence corymb-like, with elongate lower branches (Figure 1); outer disk flowers yellow when fresh .................. Pseudognaphalium |
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1b. Phyllaries light brown, yellow-brown, or green-brown to brown; capitulescence not corymb-like, either tall and slender (i.e., spike-like; Figure 2), subcapitate, or composed of axillary clusters (Figure 3); outer disk flowers purple when fresh |
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2a. Capitulescence composed of axillary clusters of capitula; involucre 2–3 mm tall; axis of plant often profusely branched (Figure 3); pappus bristles distinct but joined at the base by short, interlocking cilia ................................................................ Gnaphalium |
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2b. Capitulescence spike-like or subcapitate, in either case terminal; involucre 3–7 mm tall; axis of plant simple to sparingly branched; pappus bristles either connate at the base into a ring or distinct and without interlocking cilia |
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3a. Body of cypsela glabrous; involucre 3–5 mm tall; pappus bristles basally connate into a ring, the entire set falling as a unit; body of cypsela 0.4–0.9 mm long; plants annual or biennial, of low elevations .................................................... Gamochaeta |
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3b. Body of cypsela sparsely strigose; involucre 5–7 mm tall; pappus bristles basally connate or not; body of cypsela 1–1.5 mm long; plants perennial, boreal and alpine ........................................................................................................... Omalotheca |
Figure 1 (left), 2 (middle), and 3 (right). 1—Capitulescence architecture in Pseudognaphalium obtusifolium, note also white phyllaries and yellow disk flowers. 2—Capitulescence architecture in Omalotheca sylvatica, note also brown phyllaries and purple disk flowers. 3—Plant habit of Gnaphalium uliginosum.
Checklist of New England cudweeds
Gamochaeta pensyvanica (Willd.) Cabrera
Gamochaeta purpurea (L.) Cabrera
Gnaphalium uliginosum L.
Omalotheca supina (L.) DC.
Omalotheca sylvatica (L.) Schultz-Bip & F.W. Schultz
Pseudognaphalium macounii (Greene) Kartesz
(synonym: Gnaphalium viscosum)
Pseudognaphalium micradenium (Weatherby) Nesom
Pseudognaphalium obtusifolium (L.) Hilliard & Burtt
Literature Cited
Anderberg, A.A. 1991. Taxonomy and phylogeny of the tribe Gnaphalieae (Asteraccae). Opera Botanica 104: 1–195.
Nesom, G. 1990a. The taxonomic status of Gamochaeta (Asteraceae: Inuleae) and the species of the United States. Phytologia 68: 186–198.
Nesom, G. 1990b. Taxonomic summary of Omalotheca (Asteraceae: Inuleae). Phytologia 68: 241–246.