Euphorbia polycarpa |
Euphorbia micromera |
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smallseed sandmat |
desert spurge, Sonoran sandmat, tiny sandmat |
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Habit | Herbs, annual, with slender taproot. | |
Stems | prostrate, mat-forming, 5–35 cm, glabrous or shortly pilose. |
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Leaves | opposite; stipules distinct, subulate, 0.2–0.4 mm, pilose; petiole 0.5–1.2 mm, glabrous or pilose; blade ovate to elliptic, 6–15 × 2–4 mm, base asymmetric, one side cuneate to rounded, other side rounded, margins entire, apex obtuse, surfaces glabrous or pilose; venation obscure or only midvein conspicuous. |
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Involucre | campanulate, 0.4–0.6 × 0.5–0.9 mm, glabrous or pilose; glands 4, red, circular to oblong, 0.1 × 0.1–0.2 mm; appendages absent. |
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Staminate flowers | 2–5. |
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Pistillate flowers | ovary usually glabrous, rarely pilose; styles 0.1–0.2 mm, 2-fid at apex. |
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Capsules | oblong, 1.3–1.5 × 1.1–1.3 mm, usually glabrous, rarely pilose; columella 1–1.2 mm. |
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Seeds | light gray, narrowly ovoid, 4-angled in cross section, 0.9–1 × 0.5–0.6 mm, smooth to slightly rugose or with 1–4 faint transverse ridges that do not pass through abaxial keel. |
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Euphorbia | polycarpa is a highly variable species distributed throughout the Baja California peninsula, eastern Sonora, and the arid southwestern United States from southwestern Arizona to southern Nevada and central California. |
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l | . |
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c | . |
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Wheeler | (1941) divided the species into seven varieties, the majority of which occur in Baja California Sur. |
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He | reported two of these for the United States: var. hirtella and var. polycarpa. |
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Variety | hirtella, as the name suggests, was applied to hairy plants. |
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However | , it is here treated as a synonym of var. polycarpa, because variation in pubescence shows no geographic segregation and ranges along a continuum from glabrous or sparsely to densely hairy, and because glabrous and hairy branches can occur on the same individual. |
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Cyathia | solitary at distal nodes; peduncle 0.4–1.4 mm. |
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Euphorbia polycarpa |
Euphorbia micromera |
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Phenology | Flowering nearly year-round in response to sufficient rainfall. | |
Habitat | Desert scrub, riparian woods with ash and willow, saltbush scrub, Joshua tree woodlands and grasslands, often in sandy or gravelly areas. | |
Elevation | -20–1800 m. (-100–5900 ft.) | |
Distribution |
AZ; CA; NV; nw Mexico
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AZ; CA; NM; NV; TX; UT; Mexico (Baja California, Baja California Sur, Chihuahua, Coahuila, Durango, Sonora)
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Discussion | Varieties 5 (1 in the flora). Some of the varieties occurring in Mexico are highly divergent and appear to be sufficiently distinct to merit recognition as species. However, within the flora area, Euphorbia polycarpa is relatively uniform, and the only noteworthy variation involves the size of the involucral gland appendages. In the portion of the California Floristic Province occupied by E. polycarpa (Los Angeles, Orange, western Riverside, western San Diego, and Ventura counties) the appendages are conspicuously larger than those of plants throughout the remainder of its range in the southwestern United States (0.4–1.2 versus 0.1–0.3 mm). Large-appendaged plants are also common in Baja California and correspond well with the type collection. The taxonomic significance of this variation is not clear at this time, and the small-appendaged plants may merit segregation as an infraspecific taxon. However, no formal changes are proposed, awaiting a comprehensive review of the species throughout its range. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Source | FNA vol. 12, p. 283. | FNA vol. 12, p. 278. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Anisophyllum | Euphorbiaceae > Euphorbia > sect. Anisophyllum |
Sibling taxa | ||
Subordinate taxa | ||
Synonyms | Chamaesyce polycarpa | Chamaesyce micromera |
Name authority | Bentham: Bot. Voy. Sulphur, 50. (1844) | Boissier: Proc. Amer. Acad. Arts 5: 171. (1861) |
Web links |