Euphorbia capitellata |
Euphorbia nephradenia |
|
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capitate sandmat, head sandmat, head spurge |
Paria spurge, Utah spurge |
|
Habit | Herbs, annual or perennial, with slender to thick and woody rootstock. | Herbs, annual, with slender little-branched taproot. |
Stems | usually ascending (but ranging from decumbent to erect), 15–50 cm, glabrous, strigillose, or pilose. |
erect to ascending, branched, dichotomous distally and slightly angled, 4–25 cm, glabrous or sparsely strigillose. |
Leaves | 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. |
opposite; stipules 0.1–0.2 mm; petiole 2–6 mm, glabrous or sparsely strigillose; blade usually linear- to narrowly-elliptic, occasionally ovate to obovate, 14–42 × 3–10 mm, progressively narrower distally, base attenuate, margins entire, apex usually acute, rarely obtuse, surfaces glabrous or sparsely strigillose; venation inconspicuous. |
Involucre | 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. |
campanulate, 1–1.1 × 1.2–1.4 mm, strigillose at least toward apex; glands 5, green-yellow, oblong, 0.4–0.6 × 0.7–1 mm; appendages whitish to yellow-green, lunate to broadly ovate, 0.2–0.5 × 0.7–1.1 mm, entire or slightly crenulate. |
Staminate flowers | 25–40. |
25–30. |
Pistillate flowers | ovary glabrous or pilose; styles 0.4–0.6 mm, 2-fid entire length. |
ovary glabrous; styles 0.7–1 mm, 2-fid at apex. |
Capsules | ovoid to oblate, 1.3–1.9 × 1.4–2.1 mm, glabrous or pilose; columella 1.1–1.7 mm. |
oblate to subglobose, 2.9–3.2 × 3.2–3.4 mm, glabrous; columella 2.8–3.1 mm. |
Seeds | 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. |
light gray to whitish, oblong-ovoid, rounded in cross section, 2.3–2.6 × 1.3–1.5 mm, dimpled and rugulose; caruncle absent. |
Cyathia | 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. |
solitary at distal bifurcations of stems; peduncle 0.6–2.4 mm, glabrous or strigillose. |
2n | = 14. |
|
Euphorbia capitellata |
Euphorbia nephradenia |
|
Phenology | Flowering and fruiting year-round in response to sufficient moisture. | Flowering and fruiting spring–summer. |
Habitat | Gravelly washes, rocky slopes, basaltic talus, disturbed roadsides, primarily desert scrub, desert grasslands, riparian forests, rarely oak-juniper woodlands. | Saltbush, blackbrush, Ephedra-dominated scrub and desert communities. |
Elevation | 600–1600 m. (2000–5200 ft.) | 1100–1500 m. (3600–4900 ft.) |
Distribution |
AZ; NM; TX; Mexico (Baja California, Baja California Sur, Chihuahua, Coahuila, Sinaloa, Sonora)
|
CO; UT |
Discussion | 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.) |
Euphorbia nephradenia is the only species of the genus endemic to the Colorado Plateau of Utah and adjacent Colorado. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 262. | FNA vol. 12, p. 249. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Anisophyllum | Euphorbiaceae > Euphorbia > sect. Alectoroctonum |
Sibling taxa | ||
Synonyms | Chamaesyce capitellata, C. pycnanthema, E. pycnanthema | |
Name authority | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 188. (1859) | Barneby: Leafl. W. Bot. 10: 314. (1966) |
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