Euphorbia arizonica |
Euphorbia capitellata |
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Arizona sandmat, Arizona spurge |
capitate sandmat, head sandmat, head spurge |
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Habit | Herbs, annual or short-lived perennial, with slender to slightly thickened taproot. | Herbs, annual or perennial, with slender to thick and woody rootstock. |
Stems | erect to ascending, 10–30 cm, uniformly pilose with glistening hairs. |
usually ascending (but ranging from decumbent to erect), 15–50 cm, glabrous, strigillose, or pilose. |
Leaves | opposite; stipules distinct, deltate, (0–)0.1 mm, glabrous or with few scattered hairs; petiole 0.4–1.5 mm, pilose with glistening hairs; blade usually ovate, rarely elliptic, 3–11 × 2–7 mm, base asymmetric, one side cuneate to rounded, other side rounded to strongly cordate, margins entire, apex obtuse or acute, surfaces pilose with glistening hairs; 3-veined from base but usually only midvein conspicuous. |
opposite; stipules distinct, filiform or divided into 2–3 subulate-filiform segments, without dark, circular glands at base, 0.6–1.5 mm, pilose; petioles 0.6–1.3 mm, glabrous, pilose, or strigillose; blade ovate to narrowly ovate, 4–19 × 2–8 mm, base asymmetric, one side strongly cordate, other side rounded to slightly cordate, margins entire or serrulate (commonly nearly entire with few scattered teeth, often slightly thickened), apex acute, surfaces often with red spot in center, glabrous, pilose, or strigillose; weakly 3-veined from base, usually only midvein conspicuous. |
Involucre | urceolate, 1.1–1.3 × 0.5–0.9 mm, glabrous or pilose with glistening hairs; glands 4, dark maroon, usually oblong to reniform, rarely almost circular, 0.2 × 0.2–0.4 mm; appendages white to pink, oblong, flabellate, oblong, or elliptic, 0.3–0.6 × 0.6–0.9 mm, distal margin entire or crenulate. |
narrowly obconic to narrowly campanulate, 0.8–1.6 × 0.7–1.3 mm, glabrous or pilose; glands 4, yellow-green to pink or maroon, circular to oblong, 0.2–0.4 × 0.2–0.5 mm; appendages white to light pink, oblong to reniform or flabellate, 0.2–1.1 × 0.5–1.7 mm, surfaces glabrous, distal margin entire. |
Staminate flowers | 5–12. |
25–40. |
Pistillate flowers | ovary pilose, styles 0.5–0.6 mm, 2-fid 1/2 length. |
ovary glabrous or pilose; styles 0.4–0.6 mm, 2-fid entire length. |
Capsules | broadly ovoid to subglobose, 1.4–1.8 mm diam., pilose; columella 1.1–1.4 mm. |
ovoid to oblate, 1.3–1.9 × 1.4–2.1 mm, glabrous or pilose; columella 1.1–1.7 mm. |
Seeds | gray to light brown, ovoid, 4-angled in cross section, 0.9–1.1 × 0.5–0.6 mm, rugose with 2–5 irregular transverse ridges that sometimes pass through abaxial keel. |
pink to pinkish gray, narrowly ovoid to narrowly ovoid-oblong, 4-angled or weakly 3-angled in cross section, 0.9–1.5 × 0.5–0.7 mm, irregularly dimpled, sometimes also with faint transverse ridges that do not pass through abaxial keel. |
Cyathia | solitary at distal nodes; peduncle 0.7–3.6 mm. |
in dense, terminal capitate glomerules, with reduced, bractlike leaves subtending cyathia, at tips of main stems and short, leafy, axillary branches; peduncle 0.1–1.2 mm. |
2n | = 14. |
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Euphorbia arizonica |
Euphorbia capitellata |
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Phenology | Flowering and fruiting year-round in response to sufficient moisture. | Flowering and fruiting year-round in response to sufficient moisture. |
Habitat | Washes and rocky slopes, sometimes on limestone, desert scrub communities often with creosote-bush, riparian forests, mesquite woodlands, oak chaparral. | Gravelly washes, rocky slopes, basaltic talus, disturbed roadsides, primarily desert scrub, desert grasslands, riparian forests, rarely oak-juniper woodlands. |
Elevation | 100–1400 m. (300–4600 ft.) | 600–1600 m. (2000–5200 ft.) |
Distribution |
AZ; CA; NM; TX; Mexico (Baja California, Baja California Sur, Chihuahua, Coahuila, Durango, Sonora)
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AZ; NM; TX; Mexico (Baja California, Baja California Sur, Chihuahua, Coahuila, Sinaloa, Sonora)
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Discussion | Euphorbia arizonica is distinctive and easily recognized by its glistening, translucent hairs that appear somewhat glutinous and are most apparent on the stems. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Euphorbia capitellata is a characteristic herb in the Sonoran Desert of southern Arizona, ranging east to extreme southwestern Texas. During peak flowering, plants are attractive due to the dense clusters of cyathia with well-developed involucral gland appendages. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 260. | FNA vol. 12, p. 262. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Anisophyllum | Euphorbiaceae > Euphorbia > sect. Anisophyllum |
Sibling taxa | ||
Synonyms | Chamaesyce arizonica | Chamaesyce capitellata, C. pycnanthema, E. pycnanthema |
Name authority | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 186. (1859) | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 188. (1859) |
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