Flora of North America species comparison

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Euphorbia subg. Esula

leafy spurge, Wolf's milk
Habit Herbs or shrubs, annual, biennial, or perennial, with taproot or thickened rootstock.
Stems

woody or herbaceous (succulent in Euphorbia myrsinites), erect or ascending, branched or unbranched, terete, glabrous or hairy.
Leaves

alternate (opposite in E. lathyris);

stipules absent;

petiole present or absent, glabrous or hairy;

blade monomorphic, herbaceous (fleshy in E. myrsinites), base symmetric, margins entire or toothed, surfaces glabrous or hairy;

venation pinnate, sometimes obscure, midvein often prominent.
Involucre

± actinomorphic, not spurred;

glands 4–5 (2–3 in E. oblongata), flat or slightly convex;

appendages absent or hornlike, 2, slender with attenuate or rounded tips (thick with rounded and dilated tips in E. myrsinites).
Staminate flowers

5–40.
Pistillate flowers

ovary glabrous or hairy;

styles distinct or partly connate, usually 2-fid, sometimes unbranched.
Seeds

caruncle present.
Cyathial

arrangement: terminal pleiochasia with (1–)2–17 primary branches;

individual pleiochasial branches unbranched or 2–4 branched at 1 or more successive nodes;

bracts subtending pleiochasia (pleiochasial bracts) whorled, green, similar in shape and size to distal stem leaves or distinctly different, those on branches and subtending cyathia (dichasial and subcyathial bracts) opposite (alternate in E. trichotoma), distinct or connate;

additional cymose branches often present in axils of distal leaves, but alternately arranged and without whorled bracts.

Euphorbia subg. Esula
Distribution
Nearly worldwide
Discussion

Species ca. 480 (34 in the flora).

The European natives Euphorbia paralias and E. segetalis were recorded from Pennsylvania in the early twentieth century. Neither species has been collected more recently, and those early occurrences probably represent waifs that never became established. Other European species here considered waifs in the flora area include E. amygdaloides, E. epithymoides (sometimes treated as E. polychroma), and E. lucida. The widespread, introduced leafy spurge is treated here as E. virgata, which in North America previously has been mostly misidentified as E. esula Linnaeus. Euphorbia esula is a related, but more restricted and less weedy, European species that has been recorded historically in the flora area as a waif but is excluded because it is not persistent. Typifications and synonymy of native North American species of subg. Esula were published by D. V. Geltman et al. (2011).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaves opposite; capsules tardily dehiscent and appearing indehiscent, mesocarp spongy.
E. lathyris
1. Leaves alternate; capsules dehiscent, mesocarp not spongy.
→ 2
2. Shrubs.
E. dendroides
2. Herbs.
→ 3
3. Leaves, pleiochasial bracts, and dichasial bracts similar; dichasial bracts alternate; pleiochasial branches 3-branched at nodes; coastal areas of s Florida.
E. trichotoma
3. Leaves, pleiochasial bracts, and dichasial bracts usually dissimilar; dichasial bracts opposite; pleiochasial branches unbranched or 2-(3- or 4-)branched at each node; not coastal areas of s Florida.
→ 4
4. Cocci verrucose-tuberculate, verrucose, or papillate; involucral gland horns absent.
→ 5
5. Perennial herbs with thick rootstock or woody taproot.
→ 6
6. Leaf blade margins finely serrulate; stems often densely villous; involucral glands 2–3; capsules 3–4.5 mm; w United States.
E. oblongata
6. Leaf blade margins entire; stems glabrous; involucral glands 5; capsules 4.5–5.2 mm; e United States.
E. purpurea
5. Annual or biennial herbs with taproot.
→ 7
7. Leaves sparsely pilose, apex usually acute; terminal pleiochasial branches usually 5, 3-branched; involucre sparsely pilose.
E. platyphyllos
7. Leaves glabrous, apex usually obtuse to rounded; terminal pleiochasial branches usually 3, rarely 5, 2-branched; involucre glabrous.
→ 8
8. Cocci papillate, papillae raised, 0.2–0.5 mm; montane areas of Arizona, New Mexico.
E. alta
8. Cocci verrucose, verrucae low and round, 0.1–0.2 mm; widespread, including Arizona, New Mexico.
E. spathulata
4. Cocci smooth (granulate in E. cyparissias, granulate toward abaxial line in E. agraria and E. virgata, or puncticulate toward abaxial line in E. exigua, but then involucral gland horns always present); involucral gland horns present or absent.
→ 9
9. Perennial or biennial herbs with rootstocks (taproot in E. myrsinites).
→ 10
10. Stems succulent; leaf blades fleshy, midvein not prominent; involucral gland horns thick, tips rounded, dilated; capsules 5–7 mm.
E. myrsinites
10. Stems not succulent; leaf blades not fleshy, midvein prominent; involucral gland horns absent or slender, tips attenuate or rounded; capsules 2–5 mm (4.5–6 in E. serrata).
→ 11
11. Leaf blade and bract margins serrate, serrulate, or irregularly dentate.
→ 12
12. Leaf blade margins irregularly serrate; involucres 2–4 mm, gland horns 0–0.6 mm; capsules 4.5–6 mm.
E. serrata
12. Leaf blades margins finely serrulate; involucres 1.1–2 mm, gland horns 1–2 mm; capsules 2.5–3 mm.
E. terracina
11. Leaf blade and bract margins entire (bract margins occasionally slightly crenate in E. brachycera or slightly crenulate in E. chamaesula).
→ 13
13. Plants with slender, spreading rootstocks; seeds smooth.
→ 14
14. Leaf blades oblong-elliptic, 9–20 mm wide, bases truncate or auriculate, apices obtuse to rounded.
E. agraria
14. Leaf blades linear, linear-oblong, linear-ovate, or narrowly oblanceolate, 0.5–12 mm wide, bases attenuate, cuneate, rounded, or truncate, apices acute to rounded (sometimes mucronulate in E. virgata).
→ 15
15. Leaf blades 0.5–3 mm wide; stems 10–50 cm; cocci granulate.
E. cyparissias
15. Leaf blades 3–12 mm wide; stems 20–90 cm; cocci smooth except finely granulate toward abaxial line.
E. virgata
13. Plants from thick rootstocks; seeds shallowly pitted to almost smooth.
→ 16
16. Peduncles 1–3 mm; involucral gland horns usually convergent; capsules 4.3–5 mm.
E. chamaesula
16. Peduncles 0.3–1 mm; involucral gland horns absent or usually divergent; capsules 2–4 mm.
→ 17
17. Involucral gland margins usually entire, occasionally slightly crenate to dentate, horns longer than teeth on gland margins.
E. brachycera
17. Involucral gland margins irregularly to strongly crenate or dentate, horns absent or equaling to slightly longer than teeth on gland margins.
→ 18
18. Leaf blade apices obtuse to rounded; involucral glands oblong to broadly ovate, 0.5–0.8 × 1–1.6 mm.
E. lurida
18. Leaf blade apices acute to acuminate; involucral glands semicircular to trapezoidal, 0.8–1.5 × 1–2.2 mm.
→ 19
19. Stems and leaf blades usually glabrous and glaucous.
E. schizoloba
19. Stems and leaf blades puberulent to lanulose.
E. yaquiana
9. Annual or biennial herbs with taproots.
→ 20
20. Leaf blade margins serrulate to crenulate, sometimes only obscurely so; involucral glands without horns; seeds reticulate or areolate.
→ 21
21. Terminal pleiochasial branches usually 5; involucres 1.5–2 mm; capsules 2.5–4 mm; seeds 1.6–2.2 mm.
E. helioscopia
21. Terminal pleiochasial branches 3; involucres 0.5–0.9 mm; capsules 1.6–2 mm; seeds 1.4–1.5 mm.
E. texana
20. Leaf blade margins entire; involucral glands usually with, occasionally without, horns; seeds smooth, pitted, sulcate, or tuberculate.
→ 22
22. Seeds smooth.
E. helleri
22. Seeds pitted, sulcate, or tuberculate.
→ 23
23. Seeds sulcate at least on adaxial faces (large-pitted on abaxial faces in E. peplidion and E. peplus).
→ 24
24. Ovaries pilose at base; cocci glabrous or slightly pilose; capsules 2–3 mm; seeds transversely sulcate; involucral glands with or without horns.
E. falcata
24. Ovaries glabrous; cocci glabrous; capsules 1.3–2.3 mm; seeds longitudinally sulcate on adaxial faces, large-pitted on abaxial faces; involucral glands with horns.
→ 25
25. Leaf blades linear-oblanceolate to narrowly cuneate-spatulate, 1–4 mm wide; cocci without wings.
E. peplidion
25. Leaf blades obovate, oblong or suborbiculate, 4–15 mm wide; cocci with low longitudinal wings.
E. peplus
23. Seeds pitted or tuberculate.
→ 26
26. Seeds tuberculate.
E. exigua
26. Seeds pitted.
→ 27
27. Dichasial bracts connate 1/4–1/2 length (often only on one side or rarely only basally in E. crenulata).
→ 28
28. Biennial or occasionally annual herbs; dichasial bract margins erose-denticulate to subentire; involucral glands 1.5–2.3 mm wide, horns 0.4–0.6 mm; capsules 2.5–3 mm; seeds 2–2.5 mm; California, sw Colorado, Oregon.
E. crenulata
28. Annual herbs; dichasial bract margins entire; involucral glands 0.7–1.2 mm wide, horns 0.1–0.4 mm; capsules 2–2.7 mm; seeds 1.6–2 mm; e of Rocky Mountains.
→ 29
29. Petioles 0–3 mm; capsules ovoid-globose, 2.6–2.7 mm; seeds with deep, rounded pits in 3–4 regular, vertical rows; c United States but not Texas.
E. ouachitana
29. Petioles 2–5 mm; capsules subglobose, 2–2.5 mm; seeds with scattered, deep and broad pits; Texas.
E. roemeriana
27. Dichasial bracts usually distinct, occasionally subconnate basally.
→ 30
30. Dichasial bracts strongly imbricate; seeds gray to purple-gray or sometimes nearly black.
E. longicruris
30. Dichasial bracts not imbricate; seeds white to gray or red-brown to brown.
→ 31
31. Biennial or occasionally annual herbs; petioles of proximal leaves 5–10 mm; leaf blades usually oblanceolate to obovate, rarely ovate, 3–10 mm wide (at least some blades more than 5 mm wide); capsules 2.5–3.2 mm.
E. commutata
31. Annual herbs; petioles of proximal leaves 0–2 mm; leaf blades linear to oblanceolate, spatulate-cuneate, or slightly lanceolate, 0.5–5 mm wide; capsules 1.8–2.4 mm.
→ 32
32. Seeds reddish brown to brown, 1.3–1.4 × 0.8–0.9 mm, with 4–6 shallow pits or irregular oblong grooves on adaxial faces, small-pitted or nearly smooth on abaxial faces.
E. tetrapora
32. Seeds white to gray, 1.4–1.7 × 1–1.6 mm, with pits scattered over entire surface.
→ 33
33. Leaf blades linear to slightly lanceolate or linear-oblanceolate, 0.5–2.5 mm wide; seeds ellipsoid, 1.4–1.7 × 1–1.3 mm; sandy-soiled habitats in Texas.
E. austrotexana
33. Leaf blades oblanceolate, 3–5 mm wide; seeds ovoid, 1.6–1.7 × 1.4–1.6 mm; granitic outcrops in Georgia.
E. georgiana
Source FNA vol. 12, p. 294. Authors: Ricarda Riina, Dmitry V. Geltman, Jess A. Peirson, Paul E. Berry.
Parent taxa Euphorbiaceae > Euphorbia
Subordinate taxa
E. agraria, E. alta, E. austrotexana, E. brachycera, E. chamaesula, E. commutata, E. crenulata, E. cyparissias, E. dendroides, E. exigua, E. falcata, E. georgiana, E. helioscopia, E. helleri, E. lathyris, E. longicruris, E. lurida, E. myrsinites, E. oblongata, E. ouachitana, E. peplidion, E. peplus, E. platyphyllos, E. purpurea, E. roemeriana, E. schizoloba, E. serrata, E. spathulata, E. terracina, E. tetrapora, E. texana, E. trichotoma, E. virgata, E. yaquiana
Synonyms Galarhoeus, Tithymalus
Name authority Persoon: Syn. Pl. 2: 14. (1806)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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