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FNA | Family List | FNA Vol. 12 | Euphorbiaceae

24d. Euphorbia Linnaeus subg. Esula Persoon, Syn. Pl. 2: 14. 1806.

Ricarda Riina Dmitry V. Geltman

Jess A. Peirson Paul E. Berry

Galarhoeus Haworth; Tithymalus Gaertner

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. 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. 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.

Species ca. 480 (34 in the flora): nearly worldwide.

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).

SELECTED REFERENCES Geltman, D. V. et al. 2011. Typification and synonymy of the species of Euphorbia subgenus Esula (Euphorbiaceae) native to the United States and Canada. J. Bot. Res. Inst. Texas 5: 143–151. Norton, J. B. S. 1900. A revision of the American species of Euphorbia of the section Tithymalus occurring north of Mexico. Rep. (Annual) Missouri Bot. Gard. 11: 85–144. Peirson, J. A. et al. 2014. Phylogeny and taxonomy of the New World leafy spurges, Euphorbia section Tithymalus (Euphorbiaceae). Bot. J. Linn. Soc. 175: 191–228. Riina, R. et al. 2013. A worldwide molecular phylogeny and classification of the leafy spurges, Euphorbia subgenus Esula (Euphorbiaceae). Taxon 62: 316–342.

1 Leaves opposite; capsules tardily dehiscent and appearing indehiscent, mesocarp spongy.   106 Euphorbia lathyris
+ Leaves alternate; capsules dehiscent, mesocarp not spongy   (2)
2 (1) Shrubs.   100 Euphorbia dendroides
+ Herbs   (3)
3 (2) Leaves, pleiochasial bracts, and dichasial bracts similar; dichasial bracts alternate; pleiochasial branches 3-branched at nodes; coastal areas of s Florida.   123 Euphorbia trichotoma
+ 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 (3) Cocci verrucose-tuberculate, verrucose, or papillate; involucral gland horns absent   (5)
+ 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)
5 (4) Perennial herbs with thick rootstock or woody taproot   (6)
+ Annual or biennial herbs with taproot   (7)
6 (5) Leaf blade margins finely serrulate; stems often densely villous; involucral glands 2–3; capsules 3–4.5 mm; w United States.   110 Euphorbia oblongata
+ Leaf blade margins entire; stems glabrous; involucral glands 5; capsules 4.5–5.2 mm; e United States.   115 Euphorbia purpurea
7 (5) Leaves sparsely pilose, apex usually acute; terminal pleiochasial branches usually 5, 3-branched; involucre sparsely pilose.   114 Euphorbia platyphyllos
+ Leaves glabrous, apex usually obtuse to rounded; terminal pleiochasial branches usually 3, rarely 5, 2-branched; involucre glabrous   (8)
8 (7) Cocci papillate, papillae raised, 0.2–0.5 mm; montane areas of Arizona, New Mexico.   93 Euphorbia alta
+ Cocci verrucose, verrucae low and round, 0.1–0.2 mm; widespread, including Arizona, New Mexico.   119 Euphorbia spathulata
9 (4) Perennial or biennial herbs with rootstocks (taproot in E. myrsinites)   (10)
+ Annual or biennial herbs with taproots   (20)
10 (9) Stems succulent; leaf blades fleshy, midvein not prominent; involucral gland horns thick, tips rounded, dilated; capsules 5–7 mm.   109 Euphorbia myrsinites
+ 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 (10) Leaf blade and bract margins serrate, serrulate, or irregularly dentate   (12)
+ Leaf blade and bract margins entire (bract margins occasionally slightly crenate in E. brachycera or slightly crenulate in E. chamaesula)   (13)
12 (11) Leaf blade margins irregularly serrate; involucres 2–4 mm, gland horns 0–0.6 mm; capsules 4.5–6 mm.   118 Euphorbia serrata
+ Leaf blades margins finely serrulate; involucres 1.1–2 mm, gland horns 1–2 mm; capsules 2.5–3 mm.   120 Euphorbia terracina
13 (11) Plants with slender, spreading rootstocks; seeds smooth   (14)
+ Plants from thick rootstocks; seeds shallowly pitted to almost smooth   (16)
14 (13) Leaf blades oblong-elliptic, 9–20 mm wide, bases truncate or auriculate, apices obtuse to rounded.   92 Euphorbia agraria
+ 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 (14) Leaf blades 0.5–3 mm wide; stems 10–50 cm; cocci granulate.   99 Euphorbia cyparissias
+ Leaf blades 3–12 mm wide; stems 20–90 cm; cocci smooth except finely granulate toward abaxial line.   124 Euphorbia virgata
16 (13) Peduncles 1–3 mm; involucral gland horns usually convergent; capsules 4.3–5 mm.   96 Euphorbia chamaesula
+ Peduncles 0.3–1 mm; involucral gland horns absent or usually divergent; capsules 2–4 mm   (17)
17 (16) Involucral gland margins usually entire, occasionally slightly crenate to dentate, horns longer than teeth on gland margins.   95 Euphorbia brachycera
+ Involucral gland margins irregularly to strongly crenate or dentate, horns absent or equaling to slightly longer than teeth on gland margins   (18)
18 (17) Leaf blade apices obtuse to rounded; involucral glands oblong to broadly ovate, 0.5–0.8 × 1–1.6 mm.   108 Euphorbia lurida
+ Leaf blade apices acute to acuminate; involucral glands semicircular to trapezoidal, 0.8–1.5 × 1–2.2 mm   (19)
19 (18) Stems and leaf blades usually glabrous and glaucous.   117 Euphorbia schizoloba
+ Stems and leaf blades puberulent to lanulose.   125 Euphorbia yaquiana
20 (9) Leaf blade margins serrulate to crenulate, sometimes only obscurely so; involucral glands without horns; seeds reticulate or areolate   (21)
+ Leaf blade margins entire; involucral glands usually with, occasionally without, horns; seeds smooth, pitted, sulcate, or tuberculate   (22)
21 (20) Terminal pleiochasial branches usually 5; involucres 1.5–2 mm; capsules 2.5–4 mm; seeds 1.6–2.2 mm.   104 Euphorbia helioscopia
+ Terminal pleiochasial branches 3; involucres 0.5–0.9 mm; capsules 1.6–2 mm; seeds 1.4–1.5 mm.   122 Euphorbia texana
22 (20) Seeds smooth.   105 Euphorbia helleri
+ Seeds pitted, sulcate, or tuberculate   (23)
23 (22) Seeds sulcate at least on adaxial faces (large-pitted on abaxial faces in E. peplidion and E. peplus)   (24)
+ Seeds pitted or tuberculate   (26)
24 (23) Ovaries pilose at base; cocci glabrous or slightly pilose; capsules 2–3 mm; seeds transversely sulcate; involucral glands with or without horns.   102 Euphorbia falcata
+ 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 (24) Leaf blades linear-oblanceolate to narrowly cuneate-spatulate, 1–4 mm wide; cocci without wings.   112 Euphorbia peplidion
+ Leaf blades obovate, oblong or suborbiculate, 4–15 mm wide; cocci with low longitudinal wings.   113 Euphorbia peplus
26 (23) Seeds tuberculate.   101 Euphorbia exigua
+ Seeds pitted   (27)
27 (26) Dichasial bracts connate 1/4–1/2 length (often only on one side or rarely only basally in E. crenulata)   (28)
+ Dichasial bracts usually distinct, occasionally subconnate basally   (30)
28 (27) 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.   98 Euphorbia crenulata
+ 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 (28) 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.   111 Euphorbia ouachitana
+ Petioles 2–5 mm; capsules subglobose, 2–2.5 mm; seeds with scattered, deep and broad pits; Texas.   116 Euphorbia roemeriana
30 (27) Dichasial bracts strongly imbricate; seeds gray to purple-gray or sometimes nearly black.   107 Euphorbia longicruris
+ Dichasial bracts not imbricate; seeds white to gray or red-brown to brown   (31)
31 (30) 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.   97 Euphorbia commutata
+ 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 (31) 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.   121 Euphorbia tetrapora
+ Seeds white to gray, 1.4–1.7 × 1–1.6 mm, with pits scattered over entire surface   (33)
33 (32) 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.   94 Euphorbia austrotexana
+ Leaf blades oblanceolate, 3–5 mm wide; seeds ovoid, 1.6–1.7 × 1.4–1.6 mm; granitic outcrops in Georgia.   103 Euphorbia georgiana

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