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Published In: Species Plantarum 2: 793. 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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1. Sonchus arvensis L. (field sow thistle, perennial sow thistle)

Pl. 262 e, f; Map 1096

Plants perennial, with deep-set, branched rhizomes. Stems 40–150 cm long, often somewhat glaucous. Leaves with the clasping basal lobes rounded or pointed, the margins with the teeth having relatively stiff, short, slender prickles at the tips, the upper surface glabrous, not or only slightly shiny, the undersurface glabrous or rarely sparsely pubescent with minute, inconspicuous, unbranched hairs. Basal and lower stem leaves 6–40 cm long, usually irregularly and deeply lobed. Median and upper stem leaves gradually reduced in size, variously shallowly or deeply lobed, sometimes unlobed and merely toothed. Inflorescence branches glabrous or sparsely to moderately pubescent with spreading, gland-tipped hairs, occasionally with minute, branched, cobwebby to woolly hairs toward the tip. Flowering heads 2.5–4.5 cm in diameter (measured across the spreading corollas). Involucre (10–)14–22 mm long, glabrous or sparsely to moderately pubescent with a central band of spreading, gland-tipped hairs, occasionally with minute, branched, cobwebby to woolly hairs toward the base. Corollas 12–25 mm long, bright yellow to orangish yellow. Pappus 8–14 mm long. Fruits 2.5–3.5 mm long, noticeably 5–8-ribbed on each face, also finely cross-wrinkled, reddish brown to dark brown. 2n=36, 54. July–October.

Introduced, uncommon, known thus far only from Marion and St. Louis Counties and the city of St. Louis (native of Europe, introduced widely in North America). Railroads, gardens, and disturbed areas.

Most botanists recognize two subspecies based mainly upon differences in pubescence patterns of the inflorescence (and underlying differences in ploidy). Both types appear to be widespread weeds in North America, although usually they are not found in mixed populations. The paucity of documented chromosome counts makes it impossible to determine whether the ploidy differences are consistently correlated with the morphological characters of the subspecies.

 

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1 1. Involucres and at least the upper portions of the inflorescence branches moderately to densely pubescent with spreading, gland-tipped hairs, rarely also sparsely to moderately pubescent with minute, branched, cobwebby hairs ... 1A. SSP. ARVENSIS

Sonchus arvensis L. subsp. arvensis
2 1. Involucres and inflorescence branches glabrous or sparsely to densely pubescent with minute, branched, cobwebby to woolly hairs (toward the base of the involucre and along the adjacent branch tip), rarely also with a few spreading, gland-tipped hairs ... 1B. SSP. ULIGINOSUS Sonchus arvensis subsp. uliginosus
 
 


 

 
 
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