109. Pterocaulon Elliott, Sketch Bot. S. Carolina. 2: 323. 1823.
[Greek pteron, wing, and kaulos, stem, alluding to stems winged by decurrent leaf bases]
Guy L. Nesom
Perennials, 20–150 cm; usually rhizomatous and/or lignescent-tuberous-rooted. Stems erect, simple, internodes winged (by decurrent leaf bases), lanate-tomentose and/or glandular. Leaves cauline, alternate; sessile; blades linear to elliptic or obovate, bases decurrent, margins usually serrate to serrulate or denticulate, rarely entire, abaxial faces densely whitish-tomentose [puberulent or glabrescent], adaxial (green) glabrous or glabrescent, both faces usually stipitate- or sessile-glandular. Heads disciform, (sessile) in spiciform arrays (at ends of branches). Involucres cylindro-campanulate to campanulate, 2–3[–5] mm diam. Phyllaries persistent, in 4–6 series, distinct, narrowly lanceolate, unequal (subindurate to scarious). Receptacles flat, epaleate. Ray florets 0. Peripheral (pistillate) florets in 1–3+ series, fertile; corollas yellowish. Inner (functionally staminate [bisexual]) florets [1–]2–15[+]; corollas yellowish, lobes 5. Cypselae cylindric to fusiform, angled or slightly compressed, ribs 6–9 (white, narrow), faces usually sparsely strigose to hispidulous, minutely sessile-glandular between ribs; pappi persistent, of distinct, barbellulate bristles in 1–2 series. x = 10.
Species 17 (2 in the flora): North America, South America, Australasia.
The 11 primarily South American species of Pterocaulon sect. Pterocaulon have 1–17 functionally staminate florets per head, 1–2-seriate pappi, and hairs of tomentum with the relatively long, aseptate portion arising from clusters of basal cells. The 6 Australasian species of sect. Monenteles (Labillardière) Cabrera have a single functionally staminate floret per head, uniseriate pappi, and hairs of the tomentum equally septate throughout.
SELECTED REFERENCE
Cabrera, A. L. and A. M. Ragonese. 1978. Revisión del género Pterocaulon (Compositae). Darwiniana 21: 185–257.
