Flora of North America species comparison

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Euphorbia radians

Euphorbia sect. Poinsettia

sun spurge
Habit Herbs, perennial, with moniliform tuberous rootstock. Herbs, annual or perennial [rarely shrubs or small trees], with taproot or tuberous rootstock.
Stems

erect, 5–20(–30) cm, usually glabrous, occasionally puberulent;

branches ± straight.

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

alternate;

petiole 0–2 mm, glabrous or strigose;

blade linear-lanceolate to ovate or broadly elliptic, 25–50 × 3–20 mm, unlobed, base rounded (tapered to petiole), margins with few glandular teeth, strigillose, flat to revolute, apex acute, abaxial surface coarsely strigose, adaxial surface strigose-hirsute;

venation pinnate, midvein prominent.

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

broadly globose-cupulate, 1.7–2.1 × 2.2–2.5 mm, glabrous or puberulent;

involucral lobes divided into triangular segments;

glands 1–4(–5), white, sessile and broadly attached, 1.1 × 1.4 mm, opening oblong, glabrous;

appendages absent.

± 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

20–25.

3–25.
Pistillate flowers

ovary glabrous or puberulent, styles 3–4 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

depressed-globose, 3.8–5 × 4–5 mm, 3-lobed, glabrous or puberulent;

columella 3.6–4.5 mm.

Seeds

white, mottled brown to gray, ellipsoid, rounded in cross section, 4–4.6 × 2.4–3.2 mm, smoothly and broadly pitted or grooved;

caruncle 0.1 mm.

caruncle present or absent.
Cyathial

arrangement: terminal pleiochasial branches usually 3, occasionally reduced to congested cyme, 1–2-branched (often highly condensed);

pleiochasial bracts 6–8(–10), as tight involucrate whorl, wholly white to pale pink or red, usually narrower than distal leaves;

dichasial bracts linear and 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 2–5.5 mm.

x

= 7.

Euphorbia radians

Euphorbia sect. Poinsettia
Phenology Flowering and fruiting spring–summer.
Habitat Pinyon-juniper woodlands, oak savannas, desert grasslands and scrub.
Elevation 700–2500 m. (2300–8200 ft.)
Distribution
from FNA
AZ; TX; Mexico
[WildflowerSearch map]
[BONAP county map]
North America; Mexico; Central America; South America; West Indies; Eurasia; Africa; Indian Ocean Islands; Pacific Islands; Australia
Discussion

Euphorbia radians is widely distributed but scattered from the Sonoran and Chihuahuan deserts south to Oaxaca in Mexico. The species is distinct among species in sect. Poinsettia in the flora area in its precocious habit, often flowering before the leaves emerge.

(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. 324. 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. exstipulata, 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. 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 Poinsettia radians Poinsettia
Name authority Bentham: Pl. Hartw., 8. (1839) (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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