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FNA | Family List | FNA Vol. 5 | Polygonaceae | Eriogonum

129. Eriogonum arcuatum Greene, Pittonia. 4: 319. 1901.

Eriogonum jamesii Bentham var. arcuatum (Greene) S. Stokes

Herbs, spreading to often compact mats, 0.2-2.5 × 2-10 dm, floccose. Stems: caudex absent or spreading; aerial flowering stems erect or nearly so, slender, solid, not fistulose, usually arising directly from a taproot, 0.2-2 dm, floccose. Leaves basal, typically not in rosettes; petiole 0.5-2 cm, tomentose to floccose; blade oblanceolate or oblong to elliptic, 0.5-3 × 0.5-1.5 cm, densely tomentose abaxially, mostly floccose and grayish or greenish adaxially, margins entire, plane. Inflorescences umbellate or compound-umbellate, occasionally capitate or even reduced to single involucre, 0.3-2 × 0.3-2 dm; branches floccose; bracts 3-8, semileaflike at proximal node, 0.3-2 × 0.2-1 cm, often scalelike distally. Involucres 1 per node, usually campanulate, 3-7 × 3-8 mm, floccose; teeth 5-8, erect, 0.1-0.5 mm. Flowers 4-8 mm, including 0.7-2 mm stipelike base; perianth yellow, densely pubescent abaxially; tepals dimorphic, those of outer whorl lanceolate to elliptic, 1.5-5 × 1-3 mm, those of inner whorl lanceolate to fan-shaped, 1.5-7 × 2-4 mm; stamens exserted, 2-4 mm; filaments pilose proximally. Achenes light brown to brown, 4-5 mm, glabrous except for sparsely pubescent beak.

Varieties 3 (3 in the flora): w United States.

Eriogonum arcuatum has long been included under E. jamesii, primarily as the var. flavescens. It has also gone under the name E. bakeri, published by Greene about six weeks after he published E. arcuatum; the Fort Collins, Colorado, entomologist and botanist Charles Fuller Baker collected the types of both.

1 Involucres (3-)4-8 mm wide; inflorescences umbellate or compound-umbellate, rarely capitate; flowers (4-)5-8 mm; below 3000 m; n Arizona, c and w Colorado, nw New Mexico, e Utah, se Wyoming   129a var. arcuatum
+ Involucres 3-5 mm wide; inflorescences capitate, rarely umbellate or reduced to single involucre; flowers 4-5(-6) mm or 6-7 mm; usually above 3000 m in c Colorado, or 1600-1900 m in sw Utah   (2)
2 (1) Flowers 4-5(-6) mm; Zion National Park, Utah   129b var. rupicola
+ Flowers 6-7 mm; Rocky Mountains, Colorado   129c var. xanthum


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