E-Flora BC: Electronic Atlas of the Flora of British Columbia

Onopordum acanthium L subsp. acanthium
Scotch thistle (Scotch cottonthistle)
Asteraceae (Aster family)

Introduction to Vascular Plants

© 3CDSG DND  Email the photographer   (Photo ID #10129)

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Distribution of Onopordum acanthium subsp. acanthium
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Introduction

Scotch thistle is an introduced species of thistle in the aster family (Asteraceae) that was introduced to North America, South America and Australia in the 19th century as an ornamental plant. In North America, it is now found in disturbed sites and roadsides in most US states and in several Canadian provinces (BC, MB, NB, NS, ON, QC) (USDA 2010). In BC, it has been confirmed across the southeast and south-central part of the province, including southeastern Vancouver Island, the Lower Mainland, and the Okanagan. It has been collected as far north as Vernon. It is also reported from a few locations beyond the confirmed range in the Kootenays (Castlegar, Trail, Nelson, and Slocan areas).

This is a biennial (sometimes annual) species that produces a large rosette of spiny leaves and a large tap root (up to 30 cm long) in its first year. In the second year, it is a tall (1.5-3.0 m) coarse spiny plant with large solitary (globe-shaped) pinkish-purple flowerheads. Basal leaves are lacking, and leaves are alternate. Leaves are toothed to deeply pinnately lobed, and spines are 2-5 mm long. It is densely woolly-hairy below and sparsely woolly-hairy above, and is very drought-resistant.

This is the familiar thistle that is the emblem of Scotland.

Species Information

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General:
Biennial herb from a fibrous root; stems erect, simple, branched, broadly spiny-winged, woolly-hairy, 1.5-3.0 m tall.
Leaves:
Basal leaves lacking; stem leaves alternate; lower leaves elliptic to oblanceolate, toothed to deeply pinnately-lobed, 10-60 cm long, 5-10 cm wide, spiny, the spines 2-5 mm long, sparsely woolly-hairy and green above, densely white woolly-hairy below; upper leaves reduced and linear-elliptic to linear-lanceolate.
Flowers:
Heads discoid, few to many at the ends of branches; involucres egg-shaped to more or less rounded, 2.5-3.5 cm tall; involucral bracts lanceolate, tapering to a stiff, spreading spine 4-5 mm long, outer ones 2 mm wide at the base, inner ones similar but more flexible, flatter, and with shorter spines; disk flowers reddish-purple; receptacles flat, fleshy, honeycombed, often with short bristles on the partitions.
Fruits:
Achenes hairy, transversely wrinkled, greyish-brown, 4-5 mm long; pappus of numerous slender bristles.

Source: The Illustrated Flora of British Columbia

Habitat / Range

Dry roadsides and disturbed areas in the lowland zone; rare in SW and SC BC; introduced from Eurasia.

Source: The Illustrated Flora of British Columbia

Climate

The climate type for this species, as reported in the: "British Columbia plant species codes and selected attributes. Version 6 Database" (Meidinger et al. 2008), is not evaluated, unknown or variable.

Synonyms and Alternate Names

Onopordum acanthium L.

Taxonomic and Nomenclatural Links

Additional Photo Sources

General References