Euphorbia exstipulata |
Euphorbia angusta |
|
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square-seed spurge, squareseed or Clark Mountain spurge |
Blackfoot sandmat, narrow-leaf spurge |
|
Habit | Herbs, annual, with slender taproot. | Herbs, perennial, with moderately to strongly thickened rootstock. |
Stems | erect, 5–26 cm, uniformly puberulent to hispidulous or glabrous; branches arcuate. |
erect, 12–43 cm, uniformly strigose. |
Leaves | opposite; petiole 1–3 mm, often indistinct, glabrous or puberulent; blade linear to narrowly elliptic or ovate, 14–42 × 3–28 mm, base attenuate, margins coarsely serrate, occasionally revolute, apex acute to obtuse, abaxial surface sparsely hispidulous to strigillose, adaxial surface glabrous; midvein conspicuous. |
opposite; stipules distinct, linear-subulate or nodiform to papilliform nodiform to papilliform stipules often reddish brown, 0.1–0.7 mm, strigose; petiole 0.3–1.2 mm, strigose; blade: proximal ovate to ovate-elliptic, distal linear to elliptic-linear, 7–41 × 2–5 mm, distal leaf blades more than 6 times as long as wide, base asymmetric, cuneate to rounded, margins entire, often involute on drying, apex acute, surfaces usually short strigose, occasionally glabrous adaxially; venation pinnate, only midvein conspicuous. |
Involucre | turbinate to campanulate, 1.1–1.5 × 1–1.3 mm, glabrous, pilose or puberulent; involucral lobes divided into several linear lobes; glands 4(–5), yellow to pink, sessile and broadly attached, 0.2 × 0.3–0.4 mm, opening oblong to nearly circular, glabrous; appendages usually petaloid, white to pink, ovate to trapezoidal, occasionally absent, not incurved and covering glands, 0.2–0.4 × 0.3–0.8 mm, entire, undulate, or conspicuously divided into triangular segments, glabrous. |
turbinate to campanulate-turbinate, 1–1.5 × 1–1.4 mm, strigose; glands 4, green to yellow-green, concave, narrowly oblong, 0.2–0.4 × 0.4–0.7 mm; appendages white, flabellate, 0.5–1.1 × 0.3–0.5 mm, distal margin shallowly and irregularly toothed. |
Staminate flowers | 10–12. |
16–26. |
Pistillate flowers | ovary puberulent on keels, styles 0.8–1.1 mm, 2-fid 1/2 to nearly entire length. |
ovary strigose; styles 0.3–0.5 mm, 2-fid at apex to almost 1/2 length. |
Capsules | broadly depressed-oblong to ovoid, 2.7–3.3 × 3.1–3.9 mm, puberulent (with appressed hairs usually concentrated on keels); columella 1.9–2.5 mm. |
broadly ovoid, 2–2.6 × 2.5–3 mm, strigose; columella 1.6–2.2 mm. |
Seeds | white to gray or light brown, ovoid, bluntly 4-angled in cross section, 1.9–2.5 × 1.4–1.7 mm, tuberculate, often with 2 transverse ridges; caruncle 0.1 × 0.2 mm. |
white, ovoid, 4-angled in cross section, 1.7–2.2 × 1.1–1.2 mm, transversely low-ridged or wrinkled. |
Cyathial | arrangement: terminal cymose or dichasial branches usually 1–2, occasionally reduced to monochasia, 1–2-branched; pleiochasial bracts 2–4, often whorled, wholly green or paler green at base, similar in shape and size to distal leaves or slightly narrower; dichasial bracts similar in shape to distal leaves but smaller or highly reduced. |
|
Cyathia | peduncle 1–1.9 mm. |
solitary at distal nodes; peduncle 1.1–2.4 mm. |
2n | = 28. |
|
Euphorbia exstipulata |
Euphorbia angusta |
|
Phenology | Flowering and fruiting summer–fall. | Flowering and fruiting early spring–fall. |
Habitat | Desert scrub, grasslands, mesquite savannas, oak and oak-juniper woodlands. | Rocky limestone soils. |
Elevation | 800–2000 m. (2600–6600 ft.) | 400–1200 m. (1300–3900 ft.) |
Distribution |
AZ; CA; NM; TX; UT; WY; Mexico (Chihuahua, Coahuila, Durango, Guanajuato, San Luis Potosí, Sonora, Zacatecas)
|
TX; Mexico (Coahuila) |
Discussion | Euphorbia exstipulata is native from Texas to California and northern Mexico. The species was found once in the late nineteenth century in Wyoming but has not been re-collected there. Broad-leaved plants have been segregated as var. lata, but the variation in leaf shape is continuous and no varieties are formally recognized here. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Euphorbia angusta, which in the flora area is known from the trans-Pecos region to the Edwards Plateau, is easily recognized by its erect habit, linear leaves, and relatively showy involucral gland appendages with toothed margins. The species is closely related to E. acuta and the Mexican endemic E. johnstonii Mayfield (M. H. Mayfield 1991); it is not only morphologically distinctive but is also the only species in sect. Anisophyllum with C3 photosynthesis (R. F. Sage et al. 2011; T. L. Sage et al. 2011; G. L. Webster 1975). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 322. | FNA vol. 12, p. 260. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Poinsettia | Euphorbiaceae > Euphorbia > sect. Anisophyllum |
Sibling taxa | ||
Synonyms | E. exstipulata var. lata | Chamaesyce angusta |
Name authority | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 189. (1859) | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 189. (1859) |
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