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Published In: Species Plantarum 1: 461. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 8/11/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Introduced

 

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7. Euphorbia esula L. (leafy spurge, wolfs milk)

Map 1669, Pl. 380 i, j

Plants perennial herbs, with a deep, spreading, branched rootstock, usually also with rhizomes. Stems 30–90 cm long, erect or ascending, sometimes from a short-spreading base, often branched above the midpoint, the branches not flattened toward the tip, green to yellowish green, sometimes reddish- or purplish-tinged toward the base, glabrous. Leaves alternate above the lowermost node and below the inflorescence branches (those of the inflorescence branches opposite) not appearing crowded, sessile or very short-petiolate. Stipules absent. Leaf blades 30–100 mm long (those of the inflorescence branches 8–15 mm), unlobed, the margins entire, the surfaces glabrous, green to yellowish green; those below the inflorescence linear to narrowly oblong-lanceolate or narrowly oblanceolate, tapered at the base, rounded or abruptly short-tapered to a minute, sharply pointed tip; those along the inflorescence branches kidney-shaped to broadly ovate (slightly longer than wide to more commonly somewhat wider than long), broadly rounded or broadly angled to shallowly cordate and somewhat clasping the stem, the terminal ones somewhat cupped around the cyathia and strongly yellowish-tinged, rounded or more commonly very broadly angled to a minute, sharply pointed tip. Inflorescences terminal umbellate panicles with opposite or whorled leaves at the base and each of the 5–17 primary branches usually branched 1–4 additional times, the cyathia solitary or in small clusters at the branch tips. Involucre 1.5–3.0 mm long, glabrous, the rim shallowly 4-lobed, the margin usually densely and minutely cobwebby-hairy (the hairs attached on the inner side), the marginal glands 4, 1.2–1.9 mm long, more or less kidney-shaped to crescent, the oblong body often tapered into a pair of spreading horns, yellow to greenish yellow, lacking petaloid appendages. Staminate flowers 12–25 per cyathium. Ovaries glabrous, the styles 1.5–3.0 mm long, each divided 1/4–1/3 of the way from the tip into 2 slightly club-shaped lobes. Fruits 2.5–3.5 mm long, glabrous, appearing finely warty or roughened especially along the angles. Seeds 2.2–3.0 mm long, oblong-elliptic to oblong-ovate in outline, slightly flattened to nearly circular in cross-section, rounded or slightly flattened at the base, the surface smooth, brown to silvery gray, usually finely mottled, with a pale, somewhat flattened to slightly winglike caruncle. 2n=20, 60, 64. May–September.

Introduced, uncommon and sporadic (native of Europe, Asia; introduced in the northern U.S. south to California, New Mexico, and Virginia, also Canada). Pastures, railroads, roadsides, and open, disturbed areas.

Leafy spurge is a problem invasive exotic species throughout much of the northern half of the United States and adjacent Canada, particularly in the northern Great Plains. Dunn (1979, 1985) reviewed the history of its introduction into North America in the early 1800s and noted that more than 2.5 million acres are infested with this species. The plants have extensive rootstocks reported to reach more than 5 m deep and also produce long-lived seeds (Burrows and Tyrl, 2001). Euphorbia esula aggressively outcompetes most native grassland species, forming dense, often nearly pure stands. It has a large negative economic impact because the presence of this unpalatable species renders rangelands unfit for livestock grazing. Interestingly, young plants are palatable to sheep and goats, which are one means of controlling infestations.

The taxonomy of E. esula and its relatives (which include E. cyparissias), especially the nonnative North American populations, is still somewhat controversial. Radcliffe-Smith (1985) reviewed the taxonomy of the more than 75 taxa within the E. esula/virgata complex worldwide, concluding that about 20 species and hybrids either have been documented as growing somewhere in North America or are likely future introductions. He suggested that the most aggressively invasive member of the group was not true E. esula, but instead a hybrid between that species and another Old World species, E. virgata Waldst. & Kit. This supposed hybrid has been called E. pseudovirgata (Schur) Soó and was said to differ from E. esula in its narrow leaves generally widest below the midpoint. Steyermarks (1963) original Chariton County collection agrees with this morphology. Subsequently, Stahevich et al. (1988) and Crompton et al. (1990) conducted large-scale detailed cytological and morphometric analyses of the complex using both North American samples and additional plants from native Old World populations. They could find no chromosomal or morphological distinctions to separate E. esula and E. virgata (at least in North America) or any evidence that plants ascribed to E. pseudovirgata represented interspecific hybrids. These authors concluded that there are only five species and one hybrid present in North America and that the most widespread of these is E. esula in the broad sense (to include plants attributed to E. virgata and E. pseudovirgata). This conservative treatment is followed in the present work. The one surviving hybrid combination, E. esula E. cyparissias (E. pseudoesula Schur), has not yet been reported from Missouri but plausibly might be found in the state someday.

 


 

 
 
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