Euphorbia humistrata |
Euphorbia aaron-rossii |
|
---|---|---|
spreading sandmat |
Marble Canyon spurge, Ross' or Marble Canyon spurge |
|
Habit | Herbs, annual, with taproot. | Herbs, perennial, with deep stout 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, branched, densely clumped, previous year’s dead stems persistent, 25–45(–60) cm, glabrous, striate. |
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. |
alternate, persisting, usually reflexed, occasionally spreading; stipules 0.1–0.3 mm; petiole 0.2–2.2 mm, glabrous; blade narrowly ovate to lanceolate proximally, narrowly lanceolate, linear, or filiform distally, 10–32 × 0.5–6.5 mm, base cuneate, margins entire, apex acute, surfaces pilose when young, sparsely strigose or glabrous with age; venation obscure, only midvein conspicuous. |
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 to campanulate, 2.2–3.7 × 1.5–2.5 mm, moderately strigose; glands 5, dark green, reniform, 0.7–1.1 × 1–1.6 mm; appendages white to pink, flabellate, 0.5–1.5 × 0.8–2.2 mm, dentate or erose. |
Staminate flowers | 2–5. |
20–25. |
Pistillate flowers | ovary short-sericeous; styles 0.5–0.8 mm, 2-fid 1/2 length. |
ovary strigose; styles 1–1.3 mm, 2-fid at apex. |
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. |
subglobose, 2–3 × 4 mm, sparsely strigose; columella 2–3 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. |
gray-green to gray-brown, globose-ovoid, 1.8–2.2 × 1.2–1.6 mm, longitudinally pitted; caruncle absent. |
Cyathia | solitary at distal nodes; peduncle 0.1–0.6(–2) mm. |
in terminal monochasia (thus appearing solitary at alternate nodes); peduncle 0.5–2.5 (or 10–25) mm, glabrous or sparsely strigose. |
Euphorbia humistrata |
Euphorbia aaron-rossii |
|
Phenology | Flowering and fruiting spring–late summer. | Flowering and fruiting spring–fall. |
Habitat | Stream and river banks, gravel bars, floodplains, pond edges, disturbed fields, railroads, roadsides. | Sandy soils and dunes, occasionally rocky slopes, riparian areas. |
Elevation | 0–300 m. (0–1000 ft.) | 600–1300 m. (2000–4300 ft.) |
Distribution |
AL; AR; FL; GA; IL; IN; KS; KY; LA; MO; MS; OH; OK; TN; TX; VA; WV
|
AZ |
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 aaron-rossii is restricted to the banks of the Colorado River in several small areas of the Grand and Marble canyons. The species is most closely related to E. strictior and E. wrightii, but due to its rarity, it has not been extensively studied. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 272. | FNA vol. 12, p. 242. |
Parent taxa | Euphorbiaceae > Euphorbia > sect. Anisophyllum | Euphorbiaceae > Euphorbia > sect. Alectoroctonum |
Sibling taxa | ||
Synonyms | Chamaesyce humistrata | |
Name authority | Engelmann: in A. Gray, Manual ed. 2, 386. (1856) | A. H. Holmgren & N. H. Holmgren: Brittonia 40: 357, figs. 1, 2. (1988) |
Web links |