Gamochaeta americana (Mill.) Weddell (1856: 151)

Freire, Susana E., Grossi, Mariana A., Iharlegui, Laura, Abarca, Camila L., Monti, Claudia & Bayón, Néstor D., 2021, Taxonomic Identity of Gamochaeta americana and Gamochaeta coarctata (Gnaphalieae, Asteraceae), Phytotaxa 523 (4), pp. 273-283 : 277-280

Gamochaeta americana (Mill.) Weddell (1856: 151) .

Gnaphalium americanum Miller (1768: without page).

Gnaphalium purpureum var. americanum (Mill.) Klatt (1878: 140) . Type:— JAMAICA. 1731, W. Houston s.n .

(lectotype: BM-001009488!, designated by Moore (1936: 206); photo: E-00433391!).

Gnaphalium coarctatum Willdenow (1803: 1886) . Gnaphalium spicatum Lamarck (1788: 757) , nom. illeg. Gnaphalium purpureum var. spicatum Klatt (1878: 140) . Gamochaeta spicata Cabrera (1961: 380) , nom. superfl. Gamochaeta coarctata (Willd.) Kerguélen (1987: 104) . Type:—[ URUGUAY]. Monte Video, Oct 1767, P. Commerson s.n. (holotype: P-LAM 00309295!).

Gnaphalium consanguineum Gaudichaud (1825: 103) . Gamochaeta americana var. alpina Weddell (1856: 152) . Gnaphalium spicatum var. alpinum (Wedd.) Hieronymus (1900: 31) . Type:— ARGENTINA. Tierra del Fuego. Islas Malvinas (Falklands Islands), s.d., C. Gaudichaud s.n. (lectotype: P-00704625!, designated by Cabrera (1961: 364)).

Gnaphalium spicatum var. chonoticum Hooker (1846: 309) . Type :— CHILE. [Prov. Aysen] Chonos Arch., Dec 1834, C. Darwin [Henslow’s 333] (lectotype: K-000500392!, designated by Porter (1986: 56); isolectotype: CGE) .

Gamochaeta americana subvar. interrupta Weddell (1856: 152) . Type not designated.

Gnaphalium purpureum var. macrophyllum Greenman (1904: 97) . Type:— COSTA RICA. El Copey, 1800 m, Feb 1898, A. Tonduz 11771 (lectotype: BR-0000005318742!, designated here; isolectotype: GH-0008342 fragment!).

Gnaphalium guatemalense Gandoger (1918: 42) . Gamochaeta guatemalensis (Gand.) Cabrera (1961: 363) . Type:— GUATEMALA. Dpto. Alta Verapaz, Feb 1907, H. von Tuerckheim II 1634 (holotype: LY; isotypes: MO, NY, SI!).

Gamochaeta irazuensis Nesom (1990b: 199–200) . Type :— COSTA RICA. Volcán Irazu, 10000–11330 ft., 1 Dec 1937, P.H. Allen 702 (holotype: F-0050254 F!) .

Annual, biennial to perennial herbs, 5–67 cm tall, stem solitary or more often several ascending stems, unbranched, whitish-woolly, with basal rosette of leaves, rarely approximate, persisting at flowering. Leaves widely obovate or obovate-oblanceolate to oblanceolate, rarely linear-oblanceolate, attenuate at base, apex rounded to obtuse, mucronate, margins flat or wavy toward the apex; strongly bicolored, glabrescent or glabrous and green above, and with appressed white tomentum on lower surface; basal leaves 1.2–9(–12) cm × 3–20(–25) mm; cauline leaves 1–7.5 cm × 2–14 mm, gradually reduced in size upwards. Capitula many, in clusters in the axils of the upper leaves, arranged in continuous elongated spikes or only interrupted at the base (inflorescence branched in robust plants). Involucre narrowly campanulate, 3–5 × 2–3 mm. Phyllaries 18–30, 3–4-seriate, lamina light-brown at apex; outer phyllaries 1–3.5 × 0.5– 1.8 mm, ovate, apex obtuse or acute to acuminate, lanuginose; inner phyllaries 2.5–4.5 × 0.3–1 mm, oblong, apex acute to rounded to short acuminate, glabrous. Pistillate florets 35–136, corolla white-yellowish, purplish at apex, filiform, 2–3 mm long. Bisexual florets 2–7, corolla white-yellowish, purplish at apex, tubular, 2.2–3 mm long.Achenes 0.5–0.8 mm long, pilose, with short globose duplex hairs. Pappus bristles 2.5–3 mm long.

Distribution and habitat:— Gamochaeta americana is widely distributed from the United States of America to Tierra del Fuego and Islas Malvinas ( Falkland Islands). Adventive in Eurasia, Africa, Australia, and New Zealand, growing on grassland, moist semi-fixed dunes, and fields on the edge of forests, abandoned crop fields and modified soils along roads, from sea level to 4000 m.

Notes:— The protologue of Gnaphalium purpureum var. macrophyllum mentioned: “ Costa Rica. El Copey, altitude 1800 m, February, 1898, Ad. Tonduz, no. 11,771 (hb. Gr. and hb. Inst. Phys. Geog. Cost. Ri.)”. We located fragments of the type (leaf and spike) accompanied by an illustration at GH (00008342) and one specimen at BR (0000005318742) with the stamp of “Herb. Instit. physico-geogr. … costaricensis”. We have designated BR-0000005318742 as lectotype because it fully agrees with the protologue of the species .

Weddell (1856: 152) placed Gnaphalium americanum Mill. , G. purpureum L., G. spicatum Lam. , and G. coarctatum Willd. into the synonymy of Gamochaeta americana var. vulgaris Weddell (1856: 152) .

Nesom (2004a) described two new species, Gamochaeta argyrinea Nesom from the U.S.A. and Puerto Rico, and G. chionesthes Nesom from the U.S.A. In that treatment, Nesom excluded G. americana from the U.S.A. and referred the specimens previously identified as G. americana to G. coarctata (e.g. Nesom 1990a). Our revised concept of G. americana may also include G. argyrinea and G. chionesthes , which have bicolored obovate or obovate-oblanceolate to oblanceolate leaves and capitula arranged in elongated spikes. The multivariate analysis of Gamochaeta is one of our ongoing projects, so before synonymizing G. argyrinea and G. chionesthes with G. americana , we await the outcome of that work.