Euphorbia heterophylla
Euphorbia exserta
Mexican fireplant, painted euphorbia
coastal sand spurge, maroon or purple sand spurge
erect-ascending, 20–100 cm, sparsely pilose to villous;
branches ± straight.
erect or ascending, unbranched or branched, solitary, few, or occasionally densely clumped, previous year's dead stems not persistent, 20–33 cm, usually glabrous, rarely sparsely villous, glaucescent.
usually alternate, occasionally opposite proximally;
petiole 10–50 mm, pilose;
blade narrowly lanceolate to elliptic or broadly obovate (then usually pandurate and 4-lobed), often polymorphic on single plants, 30–200 × 20–140 mm, base acute, margins sparsely glandular-serrulate, hirtellous, flat, apex acute to obtuse, abaxial surface sparsely appressed-pilose, adaxial surface sparsely pilosulous to glabrate;
venation pinnate, midvein prominent.
alternate;
stipules less than 0.1 mm;
petiole (0–)1–3 mm, glabrous;
blade linear or linear-elliptic to obovate or orbiculate, proximal greatly reduced, scalelike, 15–30 × 1–20 mm, base cuneate to rounded, margins entire, apex rounded, broadly acute, or emarginate, surfaces glabrous, glaucescent;
venation often obscure on narrow leaves, midvein conspicuous.
usually campanulate, occasionally nearly hemispheric, 1.5–1.9 × 1.2–1.8 mm, glabrous;
involucral lobes divided into several linear, smooth lobes;
gland 1, yellow-green, stipitate, clavate, 1–1.4 × 1–1.2 mm, opening circular (occasionally flattened from pressing), with annular rim, glabrous;
appendages absent.
usually dark red, campanulate, 1.3–1.6 × 1.4–2.1 mm, glabrous;
glands 5, usually dark red, rarely greenish red, elliptic reniform, thickened, 0.3–0.5 × 0.8 mm;
appendages white or green, often forming narrow rim around distal margin of gland, 0–0.2 mm, entire.
8–15.
20–25.
ovary glabrous or puberulent;
styles 0.8–1.3 mm, 2-fid 1/2 to nearly entire length.
ovary glabrous;
styles 0.4–0.8 mm, 2-fid at apex.
broadly ovoid, 2.8–3.8 × 4–5.3 mm, 3-lobed, usually glabrous, rarely sparsely puberulent;
columella 2.1–2.8 mm.
depressed-globose, 1.8–2.5 × 3.6–4.4 mm, glabrous;
columella 1.9–2.4 mm.
brown-gray to ashy gray, broadly deltoid, 2.4–2.8 × 1.9–2.4 mm, angular in cross section, dorsal face strongly acute-carinate, tuberculate, with broad rounded tubercles in 2 rows;
caruncle 0.1 mm.
ashy white, ovoid, 2.1 × 1.3 mm, angled with 5 blunt longitudinal ridges, with shallow and irregular pits;
caruncle absent.
arrangement: terminal dichasial branches usually 2, occasionally reduced to congested cyme, 1–2-branched (often congested and difficult to discern);
pleiochasial bracts 2–4, often whorled, wholly green or paler green at base, similar in shape and size to distal leaves;
dichasial bracts highly reduced, rarely absent in highly congested clusters.
peduncle 0.9–1.5 mm.
usually in terminal dichasia, sometimes pleiochasia;
peduncle 6–33 mm, filiform, glabrous.
= 28.
Euphorbia heterophylla
Euphorbia exserta
Euphorbia heterophylla occurs from the southern United States, where it is likely naturalized, south through Mexico and Central America to South America. Because of its weediness, the precise native range in tropical and subtropical parts of the New World is not well understood. It has become widely established also in warm areas of the Old World. Leaf shape in this species is highly polymorphic within both populations and individuals. Euphorbia heterophylla can appear superficially similar to E. cyathophora but differs in its stipitate, circular involucral glands and its floral bracts that are at most very pale at the base (never colored as is typical in E. cyathophora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
K. R. Park (1998) recognized both Euphorbia exserta and E. gracilior as distinct species, with the former known only from the holotype. However, this treatment follows M. J. Huft (1997) and treats E. gracilior as a synonym of E. exserta. Although the type of E. exserta is unusual in having greenish red (versus dark red) cyathia and glands, as well as small gland appendages, it is otherwise typical of the species as a whole, including features such as the upright habit, reddish coloration, scalelike proximal leaves, and filiform peduncles to 30 mm that are also common to plants formerly treated as E. gracilior. Euphorbia gracilis Elliott, which has sometimes been applied to E. exserta, is an illegitimate name (a later homonym of E. gracilis Loiseleur-Deslongchamps) and pertains here.
The upright habit and usually dark red cyathia and glands distinguish Euphorbia exserta from the otherwise similar E. ipecacuanhae, while the glaucescent vegetative parts and smaller gland appendages readily separate E. exserta from the similar E. curtisii. Euphorbia exserta is found on the Gulf and Atlantic coastal plains.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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