Flora of North America species comparison

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Arctium tomentosum

bardane tomenteuse, cotton burdock, woolly burdock, woolly burrdock
Habit Plants to 250 cm.
Basal leaves

petioles hollow or solid, 10–15 cm, glandular-hairy;

blades 30–40 × 16–28 cm, coarsely dentate to subentire, abaxially white-tomentose, adaxially green, sparsely short-hairy.
Peduncles

1.5–12 cm.
Involucres

15–25 mm diam., densely cobwebby (rarely glabrate).
Florets

30+;

corollas rose-purple, (occasionally white), 9–13 mm, limb minutely glandular.
Phyllaries

linear to linear-lanceolate, inner usually purplish, margins with minute spreading or reflexed glandular hairs.
Heads

usually in corymbiform clusters, long-pedunculate.
Cypselae

light brown, 5–8 mm;

pappus bristles 1–3 mm.
2n

= 36.

Arctium tomentosum
Phenology Flowering summer–early fall (Jul–Oct).
Habitat Waste places, roadsides, fields, forest clearings
Elevation 0–1600 m (0–5200 ft)
Distribution
from FNA
CO; CT; MA; ME; MN; MO; ND; NH; OH; SD; VT; AB; MB; NB; NF; NS; ON; PE; QC; SK; Eurasia [Introduced in North America]
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[BONAP county map]
Discussion

Arctium tomentosum has been reported from Illinois, Iowa, Maryland, New Jersey, Oregon, Pennsylvania, South Carolina, and Wisconsin; I have not seen specimens.The involucres of Arctium tomentosum are usually very densely cobwebby.

Exceptional forms of A. tomentosum have nearly glabrous involucres. Forms of A. minus with especially cobwebby involucres have been misidentified as A. tomentosum; they lack the corymbiform capitulescence and glandular corollas of the latter.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 19, p. 169.
Parent taxa Asteraceae > tribe Cardueae > Arctium
Sibling taxa
A. lappa, A. minus
Name authority Miller: Gard. Dict. ed. 8, Arctium no. 3. (1768)
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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