Euphorbia schizoloba |
Euphorbia alta |
|
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Mojave spurge |
giant spurge, roughpod spurge, tall spurge, warty spurge |
|
Habit | Herbs, perennial, with thick rootstock. | Herbs, annual or biennial, with taproot. |
Stems | slender, ascending, often sinuous, many, densely branched near base, 10–50 cm, usually glabrous, usually glaucous. |
erect, branched, 20–60 cm, glabrous. |
Leaves | petiole 0–1 mm; blade broadly oblanceolate to obovate, 10–20 × 3–9 mm, base usually acute, occasionally short-attenuate, rarely obtuse, margins entire, apex usually acute, occasionally obtuse, acuminate to cuspidate, surfaces usually glabrous, usually glaucous; venation pinnate, sometimes obscure, midvein prominent. |
petiole 0–1 mm; blade oblong-spatulate, 20–50 × 7–18 mm, base broadly attenuate, margins serrulate, apex rounded to obtuse, surfaces glabrous, ± glaucous; venation pinnate, midvein prominent. |
Involucre | campanulate to broadly turbinate, 2.2–3 × 2–2.5 mm, glabrous; glands 4, irregularly semicircular to trapezoidal or elliptic-truncate, 0.8–1.5 × 1–2.2, margins strongly crenate or dentate; horns usually absent, if present then straight, 0.1–0.2 mm, generally equaling teeth on gland margin. |
narrowly campanulate, 0.8–1.1 × 1.1–1.3 mm, glabrous; glands 4, elliptic, 0.3–0.5 × 0.5–0.7 mm; horns absent. |
Staminate flowers | 12–20. |
5–10. |
Pistillate flowers | ovary glabrous; styles 1–1.2 mm, 2-fid. |
ovary glabrous; styles 0.5–0.9 mm, 2-fid. |
Capsules | oblong-ovoid, 3.5–4 × 3.8–5 mm, 3-lobed; cocci rounded, smooth, glabrous; columella 3.3–3.8 mm. |
depressed-globose, 2–3 × 2.5–3.5 mm, 3-lobed; cocci rounded, papillate, papillae 0.2–0.5 mm, glabrous; columella 1.5–1.9 mm. |
Seeds | gray to whitish, oblong cylindric, 2–3 × 1.5 mm, irregularly shallowly pitted to almost smooth; caruncle conic, 0.6 × 0.6 mm. |
purple-black, ovoid, 1.6–2 × 1.3–1.7 mm, reticulate and areolate; caruncle reniform, flat, 0.5 × 0.7 mm. |
Cyathial | arrangement: terminal pleiochasial branches (1–)3–4(–5), each 1–3 times 2-branched; pleiochasial bracts broadly ovate to subcordate, usually similar in size to, occasionally wider than, distal leaves; dichasial bracts distinct, broadly ovate to almost reniform, base obtuse, margins entire, apex obtuse, acuminate to cuspidate; axillary cymose branches 0–2(–4). |
arrangement: terminal pleiochasial branches 3, 2–3 times 2-branched; pleiochasial bracts elliptic-oblanceolate to oblong, similar in size to distal leaves; dichasial bracts distinct, broadly ovate to orbiculate/reniform, base obtuse, margins serrulate, apex obtuse to rounded and often mucronulate; axillary cymose branches 6–20(–25). |
Cyathia | peduncle 0.3–1 mm. |
peduncle 0.5–1 mm. |
Euphorbia schizoloba |
Euphorbia alta |
|
Phenology | Flowering and fruiting spring–summer. | Flowering and fruiting summer. |
Habitat | Desert mountains and canyon slopes, rocky and gravelly soils. | Montane pine-oak and mixed conifer forests, disturbed roadsides, logged areas. |
Elevation | 500–1800 m. (1600–5900 ft.) | 1500–3000 m. (4900–9800 ft.) |
Distribution |
AZ; CA; NV
|
AZ; NM; Mexico
|
Discussion | Euphorbia schizoloba is a desert perennial that occurs on bluffs and ledges in the Mojave and Sonoran Deserts. Sparsely pubescent plants of E. schizoloba are known from Arizona and are best represented by several collections from the Mazatzal and Sierra Ancha mountains in Gila County from between 1000 to 1800 meters. George Engelmann published two names for this species almost simultaneously in 1861 (E. schizoloba and E. incisa). Although the authors have not been able to determine which publication has priority, Engelmann himself cited E. incisa as a synonym of E. schizoloba (in W. H. Brewer et al. 1876–1880, vol. 2), as did J. B. S. Norton (1899). Also, the type specimen at MO was annotated by Engelmann as E. schizoloba, and there is no mention of the name E. incisa on the sheet. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Euphorbia alta is a montane species from southern Arizona, New Mexico, and northern and central Mexico that is very similar to and sometimes difficult to distinguish from E. spathulata. Euphorbia alta tends to be a robust biennial, whereas E. spathulata is strictly annual. The most consistent characteristic to separate these two species is that the ovaries and capsules of E. alta are distinctly papillate, with the papillae rising sharply above the surface, whereas the ovaries and capsules of E. spathulata are merely verrucose, with the protuberances lower and rounded. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 309. | FNA vol. 12, p. 298. |
Parent taxa | Euphorbiaceae > Euphorbia > subg. Esula | Euphorbiaceae > Euphorbia > subg. Esula |
Sibling taxa | ||
Synonyms | E. incisa, Tithymalus incisus, T. schizolobus | Tithymalus altus |
Name authority | Engelmann: Proc. Amer. Acad. Arts 5: 173. (1861) | Norton: N. Amer. Euphorbia, 24, plate 24. (1899) |
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