Euphorbia humistrata |
Euphorbia brachycera |
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spreading sandmat |
horned spurge, shorthorn spurge |
|
Habit | Herbs, annual, with taproot. | Herbs, perennial, with thick rootstock. |
Stems | prostrate to ascending, usually mat-forming and rooting at nodes, 5–45 cm, sparsely to moderately villous to pilose (densely on young growth). |
erect or ascending, branched, 10–60 cm, usually glabrous, sometimes puberulent. |
Leaves | opposite; stipules distinct, linear-subulate, often irregularly 2- or 3-lobed, 1–1.3 mm, sparsely villous to pilose; petiole 0.5–1.5 mm, sparsely to moderately villous to pilose; blade oblong-ovate to ovate-elliptic or oblong-elliptic, 4–18 × 2.5–8 mm, base strongly asymmetric, one side angled and other rounded to auriculate, margin on longer side serrulate, on shorter side subentire, apex rounded or broadly acute, abaxial surface pale grayish green, sparsely lanulose, adaxial surface usually with irregular reddish streak along midvein, usually glabrate, rarely sparsely lanulose; palmately veined at base, pinnate distally. |
petiole 0–0.5 mm; blade oblong-elliptic, lanceolate, or oblanceolate to broadly ovate, 5–25 × 2–7 mm, base truncate, rounded, acute, or attenuate, margins entire, apex acute or obtuse, sometimes mucronate, surfaces usually glabrous, sometimes puberulent; venation inconspicuous, only midvein prominent. |
Involucre | obconic, 0.8–1 × 0.6–0.8 mm, sparsely villous to pilose; glands 4, green to yellow-green (turning pink with age), usually ± unequal, narrowly oblong, 0.1–0.2 × 0.2–0.5 mm; appendages white to reddish tinged, lunate, ± irregular and variable in shape, 0.1–0.3 × 0.2–1.5 mm, distal margin crenulate. |
turbinate, campanulate or cupulate, 1.5–2.6 × 1.4–1.7 mm, usually glabrous, sometimes puberulent; glands 4, crescent-shaped to triangular-ovate, 0.5–0.8 × 0.7–1.7 mm, margins usually entire, occasionally slightly crenate to dentate; horns divergent, 0.2–0.4 mm, longer than teeth on gland margin. |
Staminate flowers | 2–5. |
10–15. |
Pistillate flower(s) | ovary short-sericeous; styles 0.5–0.8 mm, 2-fid 1/2 length. |
ovary, usually glabrous, sometimes puberulent; styles 0.5–0.9 mm, 2-fid. |
Capsules | ovoid, well exserted from involucre at maturity, 1.3–1.5 × 1.2–1.6 mm, sparsely to moderately short-sericeous; columella 0.9–1.2 mm. |
depressed-ovoid, 2.8–4 × 3.5–4.5 mm, 3-lobed; cocci rounded, smooth, usually glabrous, sometimes sparsely puberulent; columella 2.4–3.3 mm. |
Seeds | white to light brown, oblong-ovoid, bluntly angular in cross section, 0.8–1.2 × 0.5–0.9 mm, smooth or papillate. |
light gray, cylindric ovoid-oblong, 2–2.8(–3) × 1.4–2.2 mm, irregularly shallowly pitted; caruncle sessile to shortly stipitate, conic, 0.4–0.5 × 0.8–1.1 mm. |
Cyathia | solitary at distal nodes; peduncle 0.1–0.6(–2) mm. |
peduncle 0.4–1 mm. |
Cyathial | arrangement: terminal pleiochasial branches 3–5(–8), 1–4+ times 2-branched; pleiochasial bracts lanceolate or ovate to broadly ovate, wider than distal leaves; dichasial bracts distinct, broadly ovate or rhombic to triangular-ovate, base obtuse, margins entire or slightly crenate, apex obtuse, mucronate; axillary cymose branches 0–8. |
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2n | = 28. |
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Euphorbia humistrata |
Euphorbia brachycera |
|
Phenology | Flowering and fruiting spring–late summer. | Flowering and fruiting spring–summer. |
Habitat | Stream and river banks, gravel bars, floodplains, pond edges, disturbed fields, railroads, roadsides. | Montane areas, canyons, rock crevices, sandy or gravelly slopes, pine-oak woodlands, ponderosa pine and mixed coniferous forests. |
Elevation | 0–300 m. (0–1000 ft.) | 1200–3200 m. (3900–10500 ft.) |
Distribution |
AL; AR; FL; GA; IL; IN; KS; KY; LA; MO; MS; OH; OK; TN; TX; VA; WV
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AZ; CO; ID; MT; ND; NE; NM; SD; TX; UT; WY; Mexico (Chihuahua, Coahuila, Sonora)
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Discussion | Euphorbia humistrata is distributed throughout the Mississippi River valley and along other major river systems in the central and eastern United States. There are scattered reports of this species as a waif or as introduced farther north and/or east (for example, Minnesota, New York, North Carolina, Ontario, South Dakota, and Wisconsin), but the authors have not been able to verify these occurrences. Euphorbia humistrata is similar to E. maculata and is often confused with that species in herbaria. It can be distinguished from E. maculata by its tendency to root at the stem nodes, its longer styles, and its seeds that lack low transverse ridges and that are more bluntly angled. When growing side-by-side, E. humistrata has an overall less congested appearance and its cyathia are not as numerous or crowded as those of E. maculata. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Euphorbia brachycera is morphologically extremely variable, and plants from the northern part of the species range have sometimes been distinguished as E. robusta. Euphorbia brachycera is most closely related to the other native, perennial species of subg. Esula in western North America, namely E. chamaesula, E. lurida, E. schizoloba, and E. yaquiana. The name E. montana Engelmann, which has sometimes been applied to E. brachycera, is illegitimate because it is a later homonym of E. montana Rafinesque. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 272. | FNA vol. 12, p. 300. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Anisophyllum | Euphorbiaceae > Euphorbia > subg. Esula |
Sibling taxa | ||
Synonyms | Chamaesyce humistrata | E. brachycera var. robusta, E. montana var. robusta, E. odontadenia, E. robusta, Tithymalus brachycerus, T. robustus |
Name authority | Engelmann: in A. Gray, Manual ed. 2, 386. (1856) | Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 192. (1859) |
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