Eriogonum Michaux. Wild buckwheat [Greek erion, wool, and gony, knee, alluding to the hairy nodes of the species first described, E. tomentosum]. This key to the subgenera has been devised by James L. Reveal.
1 Flowers abruptly stipitate at the attenuated base, sometimes only weakly so, the stipe not at all winged, the bracts foliaceous, 2–several.
- 2 Tall erect perennials with a single, rarely more, leafy stem arising from a short branched caudex or a deep soft taproot; flowers white tomentose with long, dense hairs abaxially, yellowish adaxially, the stipe mostly 2–5 mm long, the outer whorl of tepals similar or narrower than those of the inner ones. 1d. subg. Eriogonum
- 2 Low spreading cespitose to shrubby perennials arising from hard, usually highly branched woody caudices; flowers mostly yellow or some shade thereof, glabrous, or if pubescent then the hairs short and not dense, the stipe 0.3–3 mm long, rarely inconspicuous and nearly lacking, the outer whorl of tepals as wide or wider than those of the inner whorl. 1e. subg. Oligogonum
1 Flowers not attenuate at base, stipelike base absent or, if present, then slightly winged; inflorescence bracts, usually 3.
- 3 Plants cespitose to tall and erect perennial herbs, subshrubs or shrubs, or if annual or biennial then the stems normally solitary, tall and leafy throughout, the flowers polygamodioecious, and the plants of c North America; involucres (except the one at the fork of the node in some) typically sessile but if distinctly pedunculate throughout then leaves neither roundish and or the plants from Texas and nc Mexico nor the perianth yellow and hispid with hirsute leaves (e.g., perennial members of subg. Ganysma).
- 4 Plants cespitose perennials, erect herbaceous perennials, subshrubs or shrubs, sometimes large and nearly arborescent, always arising from branched woody caudices; leaves tomentose to glabrous, not pilose or strigose; stems usually stout, not hollow, or if so then not jointed at the base; achenes mostly 1–5 mm long, not winged or distinctly ridged, but if ribbed then embryo curved; trans- Mississippi West and especially w North America from the Pacific Ocean to the w edge of the Great Plains. 1a. subg. Eucycla.
- 4 Plants tall and erect annuals or biennials, or if perennials then plant with pilose to strigose leaves and the stems hollow and jointed at the base or the achenes winged or distinctly ridged
- 5 Plants biennial or late-flowering annuals with long leafy stems up to 1 m or more tall; central North America from Montana and North Dakota to s New Mexico, Texas and Louisiana, and in northernmost Mexico. 1b. subg. Micrantha.
- 5 Plants perennial.
- 6 Involucres 3 at a node, sessile in the axils of the bracts, not angled but becoming ruptured at maturity by numerous foliaceous bractlets and small pubescent flowers; stems hollow and jointed basally; Death Valley area, California. 1c. subg. Clastomyelon.
- 6 Involucres solitary, pedunculate or nearly so, not ruptured by the linear bractlets or the few, usually glabrous, flowers; leaves pilose to strigose; stems usually solid but if hollow then not jointed basally; Utah, Wyoming and Nebraska s to Mexico. 1f. subg. Pterogonum
- 3 Plants annual or, if perennial, then involucres usually distinctly pedunculate, leaves basal and tomentoseat least abaxially, but if leaf blades pilose or strigose then plants of desert regions.
- 7 Involucres smooth, not ribbed or angled, usually pedunculate, or if sessile then the involucres not appressed to the branches, the involucre tube glabrous or sparsely pubescent; w North America and the n Great Plains. 1g. subg. Ganysma.
- 7 Involucres angled to strongly ribbed, strongly appressed to the branches and sessile or terminal on bracteated branchlets, or if pedunculate then the peduncles erect, stout and usually restricted to the lower nodes of the inflorescence with the involucres usually densely tomentose; w North America but mainly in California. 1h. subg. Oregonium.