Euphorbia brachycera |
Euphorbia roemeriana |
|
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horned spurge, shorthorn spurge |
Roemer's spurge |
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Habit | Herbs, perennial, with thick rootstock. | Herbs, annual, with taproot. |
Stems | erect or ascending, branched, 10–60 cm, usually glabrous, sometimes puberulent. |
erect, occasionally decumbent at base, branched, 15–30 cm, glabrous. |
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. |
petiole 2–5 mm; blade oblanceolate to obovate, 5–20 × 5–10 mm (larger leaves in distal portion of stem), base cuneate to attenuate, margins entire, apex rounded, surfaces glabrous; venation pinnate. |
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, 1.5–2 × 1–1.6 mm, glabrous; glands 4, elliptic to trapezoidal, 0.4–0.6 × 0.7–1.2 mm; horns slightly convergent, 0.1–0.3 mm. |
Staminate flowers | 10–15. |
10–12. |
Pistillate flower(s) | ovary, usually glabrous, sometimes puberulent; styles 0.5–0.9 mm, 2-fid. |
ovary glabrous; styles 0.6–1 mm, 2-fid. |
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. |
subglobose, 2–2.5 × 2.4–3 mm, slightly lobed; cocci rounded, smooth, glabrous; columella 1.5–1.8 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. |
brown, oblong-ovoid, 1.6–1.8 × 1.4–1.5 mm, with scattered, deep and broad pits; caruncle conic, reniform, 0.3–0.4 × 0.4–0.6 mm. |
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. |
arrangement: terminal pleiochasial branches 3, 1–4 times 2-branched; pleiochasial bracts ovate to oblong, similar in size to distal leaves; dichasial bracts connate 1/2 length, reniform to semicircular, base truncate to perfoliate, margins entire, apex rounded to obtuse; axillary cymose branches 0–3. |
Cyathia | peduncle 0.4–1 mm. |
peduncle 0–0.9 mm. |
2n | = 28. |
|
Euphorbia brachycera |
Euphorbia roemeriana |
|
Phenology | Flowering and fruiting spring–summer. | Flowering and fruiting spring. |
Habitat | Montane areas, canyons, rock crevices, sandy or gravelly slopes, pine-oak woodlands, ponderosa pine and mixed coniferous forests. | Rich calcareous soils, creek canyons. |
Elevation | 1200–3200 m. (3900–10500 ft.) | 100–300 m. (300–1000 ft.) |
Distribution |
AZ; CO; ID; MT; ND; NE; NM; SD; TX; UT; WY; Mexico (Chihuahua, Coahuila, Sonora)
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TX |
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.) |
D. S. Correll and M. C. Johnston (1970) suggested that Euphorbia roemeriana, which is restricted to the eastern part of the Edwards Plateau, is the southern counterpart of E. commutata, to which it is morphologically very similar. However, molecular phylogenetic analyses indicate that it is most closely related to E. austrotexana and E. longicruris (J. A. Peirson et al. 2014). Euphorbia roemeriana can be distinguished from E. commutata and several of the other small, annual species of subg. Esula by its consistently connate dichasial bracts. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 300. | FNA vol. 12, p. 308. |
Parent taxa | Euphorbiaceae > Euphorbia > subg. Esula | Euphorbiaceae > Euphorbia > subg. Esula |
Sibling taxa | ||
Synonyms | E. brachycera var. robusta, E. montana var. robusta, E. odontadenia, E. robusta, Tithymalus brachycerus, T. robustus | Tithymalus roemerianus |
Name authority | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 192. (1859) | Scheele: Linnaea 22: 151. (1849) |
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