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Mexican fireplant, painted euphorbia

euphorbia, sandmat, spurge

Habit Herbs, annual, with taproot. Herbs, subshrubs, or shrubs [trees, cactoid succulents, geophytes, vines], annual, biennial, or perennial, monoecious [dioecious]; hairs unbranched or absent; latex white.
Stems

erect-ascending, 20–100 cm, sparsely pilose to villous;

branches ± straight.

Leaves

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.

persistent, deciduous, or small and caducous proximally, alternate, opposite, or whorled, sometimes bractlike and subtending floral structures, simple;

stipules absent or present, persistent or deciduous;

petiole absent or present, glands absent;

blade unlobed, margins entire, crenulate, crenate-dentate, or serrulate, laminar glands absent;

venation palmate, palmate at base and pinnate distally, or pinnate, often only midvein prominent.

Inflorescences

bisexual [unisexual], terminal or axillary, pseudanthia (each consisting of cuplike involucre bearing glands on rim, these sometimes with petaloid appendages, enclosing solitary pistillate flower surrounded by (0–)1–80 staminate flowers, entire structure termed the cyathium), in monochasia, dichasia, pleiochasia, cymose clusters, capitate glomerules, or solitary;

glands subtending each bract 0.

Involucre

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.

Pedicels

present.

Staminate flowers

8–15.

sepals 0;

petals 0;

nectary absent;

stamen 1;

pistillode absent.

Pistillate flowers

ovary glabrous or puberulent;

styles 0.8–1.3 mm, 2-fid 1/2 to nearly entire length.

sepals 0 (ovary subtended by a calyxlike structure in E. floridana, E. inundata, E. mesembrianthemifolia, E. porteriana, E. rosescens, and E. telephioides);

petals 0;

nectary absent;

pistil 3-carpellate;

styles 3, distinct or connate basally to most of length, unbranched or 2-fid.

Fruits

capsules, tardily dehiscent and with spongy mesocarp in E. lathyris [drupes].

Capsules

broadly ovoid, 2.8–3.8 × 4–5.3 mm, 3-lobed, usually glabrous, rarely sparsely puberulent;

columella 2.1–2.8 mm.

Seeds

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.

globose to ovoid, oblong, cylindric, deltoid, pyramidal, or bottle-shaped;

caruncle present or absent.

Cyathial

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.

Cyathia

peduncle 0.9–1.5 mm.

x

= 6, 7, 8, 9, 10.

2n

= 28.

Euphorbia heterophylla

Euphorbia

Phenology Flowering and fruiting nearly year-round.
Habitat Disturbed areas, roadsides.
Elevation 0–500 m. (0–1600 ft.)
Distribution
from USDA
Mexico; Central America; South America [Introduced, Ala., Ariz., Calif., Fla., Ga., La., Miss., N.Mex., Tex.; introduced also in Eurasia, Africa]
[WildflowerSearch map]
[BONAP county map]
from USDA
North America; Mexico; Central America; South America; West Indies; Bermuda; Eurasia; Africa; Atlantic Islands; Indian Ocean Islands; Pacific Islands; Australia
[BONAP county map]
Discussion

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.)

Species ca. 2000 (139 in the flora).

Euphorbia is one of the two or three most species-rich angiosperm genera worldwide. Members of the genus occur in almost all habitat types, and many species prefer disturbed areas. Species in the genus are vegetatively highly diverse; growth forms include diminutive ephemerals, tuberous geophytes, taprooted perennial herbs, vines, various types of shrubs, trees to 25 m tall, and many xerophytic stem-succulents. Although succulents are primarily restricted to the Old World, a handful of independently derived succulents are native to the New World (B. L. Dorsey et al. 2013). Within the flora area these include E. antisyphilitica and E. tithymaloides. The striking vegetative similarity between the Old World succulent Euphorbia and New World cacti is one of the most commonly cited examples of convergent evolution.

The most distinctive feature of Euphorbia is its unique pseudanthial inflorescence, the cyathium (G. Prenner and P. J. Rudall 2007). This structure is so similar in appearance to a bisexual flower that many early botanists, including Linnaeus, actually mistook it for one. As with all Euphorbiaceae, the flowers of Euphorbia are unisexual, but in contrast to most other members of the family, they are extremely reduced. The pistillate flower comprises a single, perianth-less ovary, and the staminate flower comprises a single perianth-less stamen. Most species are likely insect-pollinated, but a few species are hummingbird-pollinated (R. L. Dressler 1957).

The latex of all of the species is abundant and in some instances highly caustic, and care should be taken to avoid exposure to it. Nevertheless, some species in the flora area have been used for medicinal purposes (for example, Euphorbia corollata and E. ipecacuanhae, C. F. Millspaugh 1892).

Euphorbia is best known for its ornamental taxa, in particular E. pulcherrima Willdenow ex Klotzsch (the Christmas poinsettia), a native of Mexico. This species is widely grown throughout the flora area but has not become naturalized. Other commonly cultivated species in the flora area include E. milii Des Moulins (crown-of-thorns), E. rigida M. Bieberstein, E. characias (Mediterranean spurge), E. marginata (snow-on-the-mountain), and E. antisyphilitica (candelilla); the last two are native species. Euphorbia “Diamond Frost” has in recent years become a popular cultivar to grow in pots or flowerbeds. Its progenitor, E. graminea, is introduced in the flora area and appears mainly associated with plantings in several southern states. In addition to several herbaceous European species that have become naturalized in North America, several others that have been recorded in the flora area in the past appear not to be persistent. These include species such as E. amygdaloides Linnaeus, E. epithymoides Linnaeus (sometimes treated as E. polychroma Kerner), E. lucida Waldstein & Kitaibel, E. paralias Linnaeus, and E. segetalis Linnaeus. In addition to these leafy taxa, numerous succulent species are commonly cultivated in botanical gardens and by private growers. Among the most popular are E. lactea Haworth, E. neriifolia Linnaeus, E. obesa Hooker, E. tirucalli Linnaeus, and E. trigona Miller. Although some of these species may persist around areas where they were previously cultivated, there is no evidence that they are actually naturalized in the region.

One of the most troublesome noxious weeds in the northern part of the flora area is leafy spurge, which was introduced from Eurasia. This species has been widely treated in North America as Euphorbia esula Linnaeus, but it turns out to be a misapplication of that name. The true leafy spurge in North America is more appropriately treated as E. virgata, a weedy species that is broadly distributed throughout temperate Europe and Asia (D. V. Geltman 1998). The actual E. esula is a related species of more restricted distribution in Europe that lacks the weedy tendencies of E. virgata (see discussion under 124. E. virgata for characters that distinguish the two). As with some of the herbaceous European waif species mentioned above, the real E. esula has been recorded historically in different parts of the flora area, but it does not appear to have persisted. It is therefore excluded here, and this should help to dispel the incorrect application of that name to leafy spurge in North America.

Historically, distinctive clades within Euphorbia were segregated into a number of satellite genera. In the flora area, these include Chamaesyce, Pedilanthus, and Poinsettia. Although these segregate genera are morphologically well-defined and monophyletic assemblages, recent molecular phylogenetic research has demonstrated that they are all nested within a broadly defined Euphorbia (V. W. Steinmann and J. M. Porter 2002; J. W. Horn et al. 2012). These molecular analyses both show Euphorbia as comprising four distinct clades, each of which is treated as a subgenus. Three of these subgenera, subg. Chamaesyce (Gray) Caesalpinius ex Reichenbach, subg. Esula Persoon, and subg. Euphorbia, are represented in the flora area. Subgenus Esula is treated here as a morphologically cohesive unit, whereas subg. Chamaesyce and subg. Euphorbia are divided into well-defined sections, which are keyed out and treated below.

The pleiochasia in Euphorbia are determinate. Each bears a whorl of pleiochasial bracts, which subtends multiple dichasial cymes, termed pleiochasial branches, that arise from a common point. The pleiochasium usually is terminated by a cyathium, but that sometimes aborts.

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

Key
1. Stems usually prostrate, sometimes erect, ascending, reclining, or decumbent; leaves opposite (rarely whorled in E. fendleri), blade bases usually asymmetric; stipules interpetiolar (except in E. acuta where at base of petiole, deciduous, sometimes appearing absent).
sect. Anisophyllum
1. Stems usually erect or ascending, rarely decumbent or prostrate; leaves alternate, opposite, or whorled, blade bases symmetric; stipules at base of petiole or absent.
→ 2
2. Stems semisucculent to succulent, zig zag; involucres strongly zygomorphic, spurred and forming tube that encloses glands.
sect. Crepidaria
2. Stems not both succulent and zig zag; involucres ± actinomorphic, not spurred.
→ 3
3. Involucral gland appendages usually petaloid, occasionally rudimentary; leaf margins entire.
sect. Alectoroctonum
3. Involucral gland appendages not petaloid (except in E. bifurcata, E. eriantha, and E. exstipulata in sect. Poinsettia, but then leaf margins usually toothed); leaf margins entire or toothed (teeth sometimes inconspicuous in E. eriantha with linear leaves).
→ 4
4. Cyathia in terminal monochasia, dichasia, or condensed pleiochasia; involucral glands shallowly cupped to deeply concave, 1–3 per cyathium (if 4–5 in E. exstipulata then involucral gland appendages present; if 4–5 in E. radians then terminal clusters of cyathia subtended by white to pinkish, leafy bracts; if 4–5 in E. eriantha, then involucral gland appendages fringed, canescent, and folded over glands); involucral gland appendages petaloid, fringed, or absent.
sect. Poinsettia
4. Cyathia in pleiochasia; involucral glands slightly concave, flat, or slightly convex, 4–5 per cyathium (2–3 in E. oblongata), terminal clusters of cyathia never subtended by white to pinkish bracts; involucral gland appendages hornlike or absent.
→ 5
5. Ovary and capsule not subtended by calyxlike structure; seeds with caruncle; involucral gland appendages hornlike or absent.
subg. Esula
5. Ovary and capsule subtended by calyxlike structure; seeds without caruncle; involucral gland appendages absent.
sect. Nummulariopsis
Source FNA vol. 12, p. 323. FNA vol. 12, p. 237. Authors: Paul E. Berry, Ricarda Riina, Jess A. Peirson, Ya Yang, Victor W. Steinmann, Dmitry V. Geltman, Jeffery J. Morawetz, Natalia I. Cacho.
Parent taxa Euphorbiaceae > Euphorbia > sect. Poinsettia Euphorbiaceae
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. 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. sect. Alectoroctonum, E. sect. Anisophyllum, E. sect. Crepidaria, E. sect. Nummulariopsis, E. sect. Poinsettia, E. subg. Esula
Synonyms E. geniculata, Poinsettia geniculata, P. heterophylla
Name authority Linnaeus: Sp. Pl. 1: 453. (1753) Linnaeus: Sp. Pl. 1: 450. (1753): Gen. Pl. ed. 5, 208. (1754)
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