Flora of North America species comparison

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Euphorbia exstipulata

Euphorbia sect. Poinsettia

square-seed spurge, squareseed or Clark Mountain spurge
Habit Herbs, annual, with slender taproot. Herbs, annual or perennial [rarely shrubs or small trees], with taproot or tuberous rootstock.
Stems

erect, 5–26 cm, uniformly puberulent to hispidulous or glabrous;

branches arcuate.

erect or ascending, branched, terete, glabrous or hairy.
Leaves

opposite;

petiole 1–3 mm, often indistinct, glabrous or puberulent;

blade linear to narrowly elliptic or ovate, 14–42 × 3–28 mm, base attenuate, margins coarsely serrate, occasionally revolute, apex acute to obtuse, abaxial surface sparsely hispidulous to strigillose, adaxial surface glabrous;

midvein conspicuous.

opposite or alternate;

stipules usually present, occasionally absent, at base of petiole;

petiole present, glabrous or hairy;

blade monomorphic (occasionally polymorphic in E. cyathophora and E. heterophylla), base symmetric, margins entire or toothed, flat to revolute, surfaces glabrous or variously hairy;

venation pinnate, midvein often prominent.
Involucre

turbinate to campanulate, 1.1–1.5 × 1–1.3 mm, glabrous, pilose or puberulent;

involucral lobes divided into several linear lobes;

glands 4(–5), yellow to pink, sessile and broadly attached, 0.2 × 0.3–0.4 mm, opening oblong to nearly circular, glabrous;

appendages usually petaloid, white to pink, ovate to trapezoidal, occasionally absent, not incurved and covering glands, 0.2–0.4 × 0.3–0.8 mm, entire, undulate, or conspicuously divided into triangular segments, glabrous.

± actinomorphic, not spurred;

glands 1–3 (sometimes 4–5 in E. eriantha, E. exstipulata, and E. radians), sessile or stipitate, shallowly cupped to deeply concave;

appendages absent or petaloid (E. bifurcata, E. eriantha, and E. exstipulata).
Staminate flowers

10–12.

3–25.
Pistillate flowers

ovary puberulent on keels, styles 0.8–1.1 mm, 2-fid 1/2 to nearly entire length.

ovary glabrous or hairy;

styles distinct, occasionally appearing connate at base, unbranched or 2-fid.
Capsules

broadly depressed-oblong to ovoid, 2.7–3.3 × 3.1–3.9 mm, puberulent (with appressed hairs usually concentrated on keels);

columella 1.9–2.5 mm.

Seeds

white to gray or light brown, ovoid, bluntly 4-angled in cross section, 1.9–2.5 × 1.4–1.7 mm, tuberculate, often with 2 transverse ridges;

caruncle 0.1 × 0.2 mm.

caruncle present or absent.
Cyathial

arrangement: terminal cymose or dichasial branches usually 1–2, occasionally reduced to monochasia, 1–2-branched;

pleiochasial bracts 2–4, often whorled, wholly green or paler green at base, similar in shape and size to distal leaves or slightly narrower;

dichasial bracts similar in shape to distal leaves but smaller or highly reduced.

arrangement: terminal monochasia, dichasia, or condensed pleiochasia with 1–3 primary branches;

individual pleiochasial branches unbranched or few-branched at 1 or more successive nodes;

bracts subtending pleiochasia (pleiochasial bracts) opposite or whorled, usually wholly green or with paler green, white, pink, or red at base, sometimes wholly white, pink, or red, similar in shape and size to distal leaves or distinctly different, those on branches and subtending cyathia (dichasial and subcyathial bracts) opposite, distinct;

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

peduncle 1–1.9 mm.

x

= 7.

Euphorbia exstipulata

Euphorbia sect. Poinsettia
Phenology Flowering and fruiting summer–fall.
Habitat Desert scrub, grasslands, mesquite savannas, oak and oak-juniper woodlands.
Elevation 800–2000 m. (2600–6600 ft.)
Distribution
from FNA
AZ; CA; NM; TX; UT; WY; Mexico (Chihuahua, Coahuila, Durango, Guanajuato, San Luis Potosí, Sonora, Zacatecas)
[WildflowerSearch map]
[BONAP county map]
North America; Mexico; Central America; South America; West Indies; Eurasia; Africa; Indian Ocean Islands; Pacific Islands; Australia
Discussion

Euphorbia exstipulata is native from Texas to California and northern Mexico. The species was found once in the late nineteenth century in Wyoming but has not been re-collected there. Broad-leaved plants have been segregated as var. lata, but the variation in leaf shape is continuous and no varieties are formally recognized here.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 30 (10 in the flora).

Section Poinsettia belongs to Euphorbia subg. Chamaesyce (Gray) Reichenbach. An expanded sect. Poinsettia is recognized here to include three species that have previously often been included in sect. Alectoroctonum (Schlechtendal) Baillon (E. bifurcata, E. eriantha, and E. exstipulata). These three species differ from the so-called core Poinsettia by the presence of involucral gland appendages, but they possess the shallowly to deeply concave involucral glands and toothed leaves that are generally diagnostic for the broader section. Molecular phylogenetic analyses clearly unite these three species with the other members of sect. Poinsettia and not with sect. Alectoroctonum (Y. Yang et al. 2012).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaf blades linear to linear-elliptic, margins entire or with 2–4 inconspicuous teeth near apex; involucral glands densely canescent, appendages divided into subulate segments, incurved and covering glands, densely canescent; styles unbranched.
E. eriantha
1. Leaf blades linear, lanceolate, ovate, oblong, elliptic, or pandurate, margins conspicuously toothed (sometimes subentire in E. cyathophora, entire or few toothed in E. pinetorum); involucral glands glabrous, appendages absent or entire, undulate, slightly lobed, or divided into triangular segments, not incurved and covering glands, glabrous; styles 2-fid.
→ 2
2. Branches often arcuate; involucral gland appendages usually present, rarely absent.
→ 3
3. Leaf blades usually ovate, rarely oblong or elliptic, margins finely serrulate; petioles 15–49 mm; involucral glands 1(–3); ovaries glabrous; caruncles absent or rudimentary.
E. bifurcata
3. Leaf blades linear to narrowly elliptic or ovate, margins coarsely serrate; petioles 1–3 mm; involucral glands 4 (–5); ovaries puberulent on keels; caruncles 0.1 × 0.2 mm.
E. exstipulata
2. Branches ± straight (except occasionally proximal branches arcuate in E. davidii and E. dentata); involucral gland appendages absent.
→ 4
4. Leaves usually opposite, occasionally alternate distally, blade margins coarsely crenate-dentate or doubly crenate; seeds with caruncles; pleiochasial bracts wholly green or with paler green, white, or mauve near base; annual herbs.
→ 5
5. Ovaries densely pilose; capsules pilose (often sparsely); involucral gland taller than wide, stipitate.
E. cuphosperma
5. Ovaries and capsules glabrous or sparsely strigose; involucral glands shorter than wide, sessile.
→ 6
6. Hairs of abaxial leaf blade surface stiff, strongly tapered; capsules 4–4.8 mm wide; seeds angular in cross section, unevenly tuberculate.
E. davidii
6. Hairs of abaxial leaf blade surface weak, filiform; capsules 3.5–4 mm wide; seeds rounded in cross section, evenly tuberculate.
E. dentata
4. Leaves usually alternate, occasionally opposite proximally, blade margins entire, subentire, or glandular-serrulate; seeds usually without caruncles, occasionally caruncles rudimentary; pleiochasial bracts green (purpurescent in E. pinetorum), often paler green, white, pink, or red at base, occasionally wholly white, pink, or red; annual or perennial herbs.
→ 7
7. Stems 5–20(–30) cm, from moniliform tuberous rootstocks; seeds 4–4.6 mm; perennial herbs.
E. radians
7. Stems 20–100 cm, with taproots or woody rootstocks; seeds 2.1–3.1 mm; annual or perennial herbs.
→ 8
8. Pleiochasial bracts wholly green or paler green at base; involucral glands stipitate, opening round (occasionally flattened from pressing), with annular rim.
E. heterophylla
8. Pleiochasial bracts green or purpurescent, often white, pink, or red at base, occasionally wholly white, pink, or red; involucral glands sessile or substipitate, opening oblong (flattened without pressing), without annular rim.
→ 9
9. Annual herbs with spreading taproots; leaf blades 4–40 mm wide, linear, lanceolate, elliptic, or broadly pandurate; bracts usually green with white, pink, or red at base, occasionally distal bracts wholly white, pink, or red, rarely all bracts wholly green; capsules green; involucral gland 1; widespread, including s Florida.
E. cyathophora
9. Perennial herbs with thickened, woody taproots; leaf blades 2.5–5 mm wide, lanceolate to linear; bracts wholly purpurescent green or pink at base; capsules purpurescent; involucral glands 3(–5); Miami-Dade and Monroe counties, s Florida.
E. pinetorum
Source FNA vol. 12, p. 322. FNA vol. 12, p. 317. Authors: Jess A. Peirson, Paul E. Berry, Victor W. Steinmann.
Parent taxa Euphorbiaceae > Euphorbia > sect. Poinsettia Euphorbiaceae > Euphorbia
Sibling taxa
E. aaron-rossii, E. abramsiana, E. acuta, E. agraria, E. albomarginata, E. alta, E. angusta, E. antisyphilitica, E. arizonica, E. astyla, E. austrotexana, E. bicolor, E. bifurcata, E. bilobata, E. blodgettii, E. bombensis, E. brachycera, E. capitellata, E. carunculata, E. chaetocalyx, E. chamaesula, E. cinerascens, E. commutata, E. conferta, E. cordifolia, E. corollata, E. crenulata, E. cumulicola, E. cuphosperma, E. curtisii, E. cyathophora, E. cyparissias, E. davidii, E. deltoidea, E. dendroides, E. dentata, E. discoidalis, E. eriantha, E. exigua, E. exserta, E. falcata, E. fendleri, E. florida, E. floridana, E. garberi, E. georgiana, E. geyeri, E. glyptosperma, E. golondrina, E. gracillima, E. graminea, E. helioscopia, E. helleri, E. heterophylla, E. hexagona, E. hirta, E. hooveri, E. humistrata, E. hypericifolia, E. hyssopifolia, E. indivisa, E. innocua, E. inundata, E. ipecacuanhae, E. jaegeri, E. jejuna, E. laredana, E. lasiocarpa, E. lata, E. lathyris, E. longicruris, E. lurida, E. macropus, E. maculata, E. marginata, E. meganaesos, E. melanadenia, E. mendezii, E. mercurialina, E. mesembrianthemifolia, E. micromera, E. misera, E. missurica, E. myrsinites, E. nephradenia, E. nutans, E. oblongata, E. ocellata, E. ophthalmica, E. ouachitana, E. parishii, E. parryi, E. pediculifera, E. peplidion, E. peplus, E. perennans, E. pergamena, E. pinetorum, E. platyphyllos, E. platysperma, E. polycarpa, E. polygonifolia, E. polyphylla, E. porteriana, E. prostrata, E. pubentissima, E. purpurea, E. radians, E. rayturneri, E. revoluta, E. roemeriana, E. rosescens, E. schizoloba, E. serpens, E. serpillifolia, E. serrata, E. serrula, E. setiloba, E. simulans, E. spathulata, E. stictospora, E. strictior, E. telephioides, E. terracina, E. tetrapora, E. texana, E. theriaca, E. thymifolia, E. tithymaloides, E. trachysperma, E. trichotoma, E. vallis-mortae, E. velleriflora, E. vermiculata, E. villifera, E. virgata, E. wrightii, E. yaquiana
Subordinate taxa
E. bifurcata, E. cuphosperma, E. cyathophora, E. davidii, E. dentata, E. eriantha, E. exstipulata, E. heterophylla, E. pinetorum, E. radians
Synonyms E. exstipulata var. lata Poinsettia
Name authority Engelmann: in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 189. (1859) (Graham) Baillon: Étude Euphorb., 284. (1858)
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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