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©Copyright 1993 by the Regents of the University of California
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POLYGONACEAE

BUCKWHEAT FAMILY

James C. Hickman

Annual to trees, some dioecious
Stem: nodes often swollen
Leaves simple, basal or cauline, alternate, opposite, or whorled, generally entire; stipules 0 or obvious and fused into a generally scarious sheath around stem
Inflorescence: small cluster, axillary or arrayed in cymes or panicles; involucres sometimes subtending 1–many flowers
Flower generally bisexual, small, ± radial; perianth generally 5–6-lobed, base ± tapered, often jointed to pedicel; stamens 2–9, often in 2 whorls; ovary superior, styles generally 3, generally fused at base
Fruit: achene, generally enclosed by persistent perianth, generally 3-angled, ovoid, and glabrous
Genera in family: 50 genera, 1100 species: worldwide, especially n temp; some cultivated for food (Fagopyrum ; Rheum , rhubarb; Rumex , sorrel) or ornamental (Antigonon , coral-vine; Muehlenbeckia ; Polygonum )
Reference: [Ronse Decraene & Akeroyd 1988 Bot J Linn Soc 98:321–371; Reveal et al. 1989 Phytologia 66(2–4):83–414]
Treatments of the 15 eriogonoid genera are based on the monographic work of James L. Reveal, who is gratefully acknowledged.

DODECAHEMA


Species in genus: 1 sp
Etymology: (Greek: twelve awns)
Reference: [Reveal & Hardham 1989 Phytologia 66:83–88]

Native

D. leptoceras (A. Gray) Reveal & Hardham

SLENDER-HORNED SPINEFLOWER

Annual, spreading, 3–10 cm
Leaves basal; stipule 0; petiole 0; blade 10–60 mm, linear-oblanceolate, glabrous
Inflorescence 1–5 dm diam; bract 1 per node, 3–6 mm, 3-lobed; involucre ± sessile, 2–4 mm, cylindric, glandular, lobes 6, lobe awns 2–3 mm, awns at base 6, 1–2 mm; flowers 3 per involucre
Flower: perianth 1.2–2 mm, white to pink, hairy, lobes 6; stamens 9
Fruit 1.7–2 mm, dark brown to black
Chromosomes: n=±17
Ecology: Alluvial sand in coastal scrub
Elevation: 200–700 m.
Bioregional distribution: c&e South Coast, adjacent foothills of Transverse Ranges, Peninsular Ranges
Synonyms: Centrostegia l. A. Gray; Chorizanthe l. (A. Gray) S. Watson
Threatened by development, off-road vehicles.

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