74. Pleiacanthus (Nuttall) Rydberg, Fl. Rocky Mts. 1069. 1917.
Thorny skeletonweed [Greek pleio, in compounds, more than usual, and acanthos, a prickly plant, or acantha, thorn]
L. D. Gottlieb
Lygodesmia D. Don subgen. Pleiacanthus Nuttall, Trans. Amer. Philos. Soc., n. s. 7: 444. 1841
Perennials, 10–50 cm; root crowns woody, branched. Stems 1–4[–8]. branches divaricate, rigid, spine-tipped, with conspicuous tufts of light brown, wool in axils of bud scales at and just below ground level, otherwise glabrous (bud scales lanceolate, 8–30 × 5–8 mm, entire). Leaves cauline; sessile; proximal blades linear, margins entire; distal bractlike. Heads (± subsessile, erect), borne singly or in paniculiform arrays. Peduncles not inflated, not bracteate. Calyculi of 4–6 bractlets (unequal, lengths to 1/2 phyllaries). Involucres cylindric. 2–3+ mm diam. Phyllaries 3–5 in ±1 series, linear-lanceolate. Receptacles flat or convex. smooth, glabrous, epaleate. Florets 3–5; corollas pink or lavender. Cypselae tan, columnar, apices truncate (beaks 0), with 5 equal faces. separated by weakly rounded ribs, each face with central. narrow, shallow, longitudinal groove, glabrous; pappi persistent, of 50–60, distinct, light tan, barbellate bristles (of 2 lengths). x = 8.
Species 1: w United States
