26. Acaena Mutis ex Linnaeus, Mant. Pl. 145, 200. 1771.
[Greek akaina, thorn, alluding to barbed spines arising from wall of hypanthium]
Herbs, perennial, 1–15 dm diam.; from branched, woody caudex or stoloniferous. Stems 1–20, creeping and rooting or suberect, ˂basally woody, clad in old leaf bases˃, glabrous or sparsely pilose. Leaves persistent, basal and/or cauline; stipules absent or persistent, adnate to petiole, free portion ovate to obovate, deeply 2–5-fid, or linear, margins entire; petiole present; blade spatulate, [1–]2–15[–18] cm, herbaceous, leaflets 4–10 per side, ˂opposite˃, ovate, oblong, or elliptic, margins flat or revolute, incised or pinnatisect, dentate or entire, surfaces hairy or glabrous. Inflorescences terminal or axillary, [4–]15–100-flowered, spikes or globose heads; peduncles present or absent; bracts absent; bracteoles present. Pedicels present. Flowers 3.5–6 mm diam.; hypanthium obtriangular, ovoid, or obconic, 3.5–6 mm diam., ˂spiny [or winged or neither]˃, tomentose or glabrous; sepals 4–5[–6], spreading, elliptic or triangular; petals 0; stamens 2–4[–6], longer than sepals; carpels 1[or 2], ˂styles white or red, fimbriate˃. Fruits achenes, 1[–2], spindle-shaped; hypanthium persistent, enclosing achenes, ˂gray- to red-brown, ovoid, oblong, globose, or obconic, 3–6 mm diam., hardened, sometimes winged, distinctly or obscurely angled with a single spine at apex of each of 4 angles, or covered with 10–20[–50] spines [or without spines], spines usually bearing retrorse hairs or barbs at apices, pubescent or glabrous, eglandular or glandular˃; sepals persistent, spreading. x = 21.
Species ca. 45 (3 in the flora): w United States, Mexico, South America (Argentina, Chile), s Africa (Cape Province), Atlantic Islands (Gough Island, South Georgia, Tristan da Cunha), Indian Ocean Islands (Kerguelen, Prince Edward Island), Pacific Islands (Hawaii, New Guinea, New Zealand), Australia; introduced in Europe (England, Ireland).
SELECTED REFERENCE Bitter, F. A. G. [1910–]1911. Die Gattung Acaena. Biblioth. Bot. 74.