Euphorbia brachycera |
Euphorbia micromera |
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horned spurge, shorthorn spurge |
desert spurge, Sonoran sandmat, tiny sandmat |
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Habit | Herbs, perennial, with thick rootstock. | Herbs, annual, with slender taproot. |
Stems | erect or ascending, branched, 10–60 cm, usually glabrous, sometimes puberulent. |
prostrate, mat-forming, 5–35 cm, glabrous or shortly pilose. |
Leaves | petiole 0–0.5 mm; blade oblong-elliptic, lanceolate, or oblanceolate to broadly ovate, 5–25 × 2–7 mm, base truncate, rounded, acute, or attenuate, margins entire, apex acute or obtuse, sometimes mucronate, surfaces usually glabrous, sometimes puberulent; venation inconspicuous, only midvein prominent. |
opposite; stipules distinct, subulate, 0.2–0.4 mm, pilose; petiole 0.5–1.2 mm, glabrous or pilose; blade ovate to elliptic, 6–15 × 2–4 mm, base asymmetric, one side cuneate to rounded, other side rounded, margins entire, apex obtuse, surfaces glabrous or pilose; venation obscure or only midvein conspicuous. |
Involucre | turbinate, campanulate or cupulate, 1.5–2.6 × 1.4–1.7 mm, usually glabrous, sometimes puberulent; glands 4, crescent-shaped to triangular-ovate, 0.5–0.8 × 0.7–1.7 mm, margins usually entire, occasionally slightly crenate to dentate; horns divergent, 0.2–0.4 mm, longer than teeth on gland margin. |
campanulate, 0.4–0.6 × 0.5–0.9 mm, glabrous or pilose; glands 4, red, circular to oblong, 0.1 × 0.1–0.2 mm; appendages absent. |
Staminate flowers | 10–15. |
2–5. |
Pistillate flower(s) | ovary, usually glabrous, sometimes puberulent; styles 0.5–0.9 mm, 2-fid. |
ovary usually glabrous, rarely pilose; styles 0.1–0.2 mm, 2-fid at apex. |
Capsules | depressed-ovoid, 2.8–4 × 3.5–4.5 mm, 3-lobed; cocci rounded, smooth, usually glabrous, sometimes sparsely puberulent; columella 2.4–3.3 mm. |
oblong, 1.3–1.5 × 1.1–1.3 mm, usually glabrous, rarely pilose; columella 1–1.2 mm. |
Seeds | light gray, cylindric ovoid-oblong, 2–2.8(–3) × 1.4–2.2 mm, irregularly shallowly pitted; caruncle sessile to shortly stipitate, conic, 0.4–0.5 × 0.8–1.1 mm. |
light gray, narrowly ovoid, 4-angled in cross section, 0.9–1 × 0.5–0.6 mm, smooth to slightly rugose or with 1–4 faint transverse ridges that do not pass through abaxial keel. |
Cyathial | arrangement: terminal pleiochasial branches 3–5(–8), 1–4+ times 2-branched; pleiochasial bracts lanceolate or ovate to broadly ovate, wider than distal leaves; dichasial bracts distinct, broadly ovate or rhombic to triangular-ovate, base obtuse, margins entire or slightly crenate, apex obtuse, mucronate; axillary cymose branches 0–8. |
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Cyathia | peduncle 0.4–1 mm. |
solitary at distal nodes; peduncle 0.4–1.4 mm. |
2n | = 28. |
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Euphorbia brachycera |
Euphorbia micromera |
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Phenology | Flowering and fruiting spring–summer. | Flowering nearly year-round in response to sufficient rainfall. |
Habitat | Montane areas, canyons, rock crevices, sandy or gravelly slopes, pine-oak woodlands, ponderosa pine and mixed coniferous forests. | Desert scrub, riparian woods with ash and willow, saltbush scrub, Joshua tree woodlands and grasslands, often in sandy or gravelly areas. |
Elevation | 1200–3200 m. (3900–10500 ft.) | -20–1800 m. (-100–5900 ft.) |
Distribution |
AZ; CO; ID; MT; ND; NE; NM; SD; TX; UT; WY; Mexico (Chihuahua, Coahuila, Sonora)
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AZ; CA; NM; NV; TX; UT; Mexico (Baja California, Baja California Sur, Chihuahua, Coahuila, Durango, Sonora)
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Discussion | Euphorbia brachycera is morphologically extremely variable, and plants from the northern part of the species range have sometimes been distinguished as E. robusta. Euphorbia brachycera is most closely related to the other native, perennial species of subg. Esula in western North America, namely E. chamaesula, E. lurida, E. schizoloba, and E. yaquiana. The name E. montana Engelmann, which has sometimes been applied to E. brachycera, is illegitimate because it is a later homonym of E. montana Rafinesque. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Source | FNA vol. 12, p. 300. | FNA vol. 12, p. 278. |
Parent taxa | Euphorbiaceae > Euphorbia > subg. Esula | Euphorbiaceae > Euphorbia > sect. Anisophyllum |
Sibling taxa | ||
Synonyms | E. brachycera var. robusta, E. montana var. robusta, E. odontadenia, E. robusta, Tithymalus brachycerus, T. robustus | Chamaesyce micromera |
Name authority | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 192. (1859) | Boissier: Proc. Amer. Acad. Arts 5: 171. (1861) |
Web links |