Euphorbia davidii |
Euphorbia serpillifolia |
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David's poinsettia, David's spurge, tooth poinsettia, tooth spurge |
thyme leaf spurge, thyme-leafed spurge, thymeleaf sandmat |
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Habit | Herbs, annual, with taproot. | Herbs, annual, with slender taproot. | ||||
Stems | erect or ascending, 20–70 cm, both coarsely and sparsely hirsute and closely strigillose; branches usually ± straight, occasionally proximal branches arcuate. |
prostrate to ascending, often mat-forming, 7–35 cm, glabrous, pilose, or villous. |
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Leaves | usually opposite, occasionally alternate at distal nodes; petiole 7–25 mm, strigose; blade usually narrowly to broadly elliptic, occasionally lance-elliptic, 10–100 × 5–35 mm, base cuneate to attenuate, margins coarsely crenate-dentate, strigose, revolute to nearly flat, apex broadly acute to acuminate, or obtuse, abaxial surface strigose with stiff, strongly tapered hairs, adaxial surface sparsely strigose-hirsute; venation pinnate, midvein prominent. |
opposite; stipules distinct, divided nearly to base into 3–5 subulate to filiform segments, these sometimes 2-fid toward apex or laciniate, 0.7–2.1 mm, glabrous; petiole 0.5–1 mm, glabrous, villous, or pilose; blade ovate, oblong, elliptic, or obovate, 3–13 × 2–7 mm, base asymmetric, rounded to oblique, margins usually entire in proximal 1/2 and serrulate in distal 1/2, rarely serrulate nearly to base, apex obtuse or truncate, surfaces often with red spot in center, not papillate, glabrous, villous, or pilose; weakly 3-veined from base, usually only midvein conspicuous. |
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Involucre | cylindric, 2.5–3 × 1.3–1.8 mm, glabrous; involucral lobes divided into 5–7 linear, papillate lobes; gland 1, yellow-green, sessile and broadly attached, 0.9 × 1.3 mm, opening oblong, glabrous; appendages absent. |
obconic, 0.6–1.1 × 0.6–1 mm, glabrous, villous, or pilose; glands 4, yellow to pink, usually oblong to reniform, 0.1 × 0.2–0.3 mm; appendages white to pink, oblong or flabellate, rarely absent, (0–)0.1–0.2 × (0–)0.3–0.4 mm, distal margin entire or shallowly lobed. |
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Staminate flowers | 5–8. |
5–20. |
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Pistillate flowers | ovary glabrous or sparsely strigose; styles 1 mm, 2-fid 1/2 to nearly entire length. |
ovary glabrous, villous, or pilose; styles 0.3–0.4 mm, 2-fid 1/2 length. |
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Capsules | broadly ovoid, 2.9–3.3 × 4–4.8 mm, 3-lobed, glabrous; columella 2.2–2.7 mm. |
broadly ovoid to oblate, cocci not elongated nor terminating in empty portion, 1.4–1.9 × 1.5–2, glabrous, pilose, or villous; columella 1.2–1.6 mm. |
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Seeds | black to brown or pale gray, ovoid to triangular-ovoid, angular in cross section, 2.4–2.9 × 2.2–2.9 mm, low-tuberculate, tubercles irregularly arranged or in faint, transverse row; caruncle 0.9–1.1 mm. |
pink, light brown, or grayish, ovoid to narrowly ovoid, 4-angled in cross section, 1–1.4 × 0.6–0.9 mm, smooth to dimpled or rugose, or with faint transverse ridges that do not interrupt abaxial keel. |
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Cyathial | arrangement: terminal pleiochasial branches usually 3, occasionally reduced to congested cyme, 1–2-branched; pleiochasial bracts 2–4, often whorled, green with diffuse greenish white to mauve near base, similar in shape and size to distal leaves or slightly narrower; dichasial bracts similar in shape to distal leaves but smaller, often highly reduced. |
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Cyathia | peduncle 0.5–1 mm. |
solitary or in small, cymose clusters at distal nodes or on congested, axillary branches; peduncle 0.4–1.7 mm. |
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2n | = 56. |
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Euphorbia davidii |
Euphorbia serpillifolia |
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Phenology | Flowering and fruiting summer–fall. | |||||
Habitat | Forests, stream and riverbanks, prairies, roadsides and open disturbed areas. | |||||
Elevation | 200–1500 m. (700–4900 ft.) | |||||
Distribution |
AR; AZ; CA; CO; FL; IA; ID; IL; IN; KS; KY; LA; MA; MI; MN; MO; NC; NE; NJ; NM; NY; OH; OK; SD; TN; TX; UT; VA; VT; WI; WV; WY; ON; QC; Mexico (Chihuahua, Coahuila, Sonora) [Introduced in South America, Eurasia (China, Russia), Australia]
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AZ; CA; CO; FL; GA; IA; ID; IL; MI; MN; MO; MT; ND; NE; NH; NM; NV; NY; OK; OR; PA; SD; TX; UT; WA; WI; WY; AB; BC; MB; NB; ON; QC; SK; Mexico; South America |
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Discussion | Euphorbia davidii is native from the southwestern United States and northern Mexico north through the southern Great Plains; it apparently is adventive elsewhere. The species is the weediest member of the E. dentata species group (following M. H. Mayfield 1997) and has become an agricultural weed in North America, South America (for example, Argentina), and in the Old World (particularly Australia and Russia). Euphorbia davidii can be distinguished from the closely similar E. dentata by its larger capsules and seeds, often more elliptic leaves, and shorter, stiffer hairs. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Subspecies 2 (2 in the flora). Euphorbia serpillifolia is variable, especially in regard to seed sculpturing. L. C. Wheeler (1941) documented and discussed this variation, suggesting that within the United States and Canada the taxon could be further divided into various taxa. However, Wheeler refrained from actually proposing names and commented that further study was needed. The authors concur with Wheeler and maintain a broad delimitation of the species, pending a detailed study of variation throughout its range. Otherwise indistinguishable hairy plants are treated as subsp. hirtula. In contrast to the widespread typical subspecies, subsp. hirtula ranges from northern Baja California, Mexico, to central California. In this region the two subspecies sometimes grow together. The spelling of the specific epithet follows the original publication of the name and contrasts with the often-used variant serpyllifolia. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 12, p. 320. | FNA vol. 12, p. 287. | ||||
Parent taxa | Euphorbiaceae > Euphorbia > sect. Poinsettia | Euphorbiaceae > Euphorbia > sect. Anisophyllum | ||||
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Subordinate taxa | ||||||
Synonyms | Chamaesyce serpillifolia | |||||
Name authority | Subils: Kurtziana 17: 125, figs. 1, 2H–J. (1984) | Persoon: Syn. Pl. 2: 14. (1806) | ||||
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