Ontario Weeds: Bull thistle
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Excerpt from Publication 505, Ontario Weeds, Order this publication
Table of Contents
Name: Bull thistle, Cirsium vulgare
(Savi) Tenore.,
Other Names: CIRVU, chardon vulgaire,
Spear thistle, cirse vulgaire, pet-d'âne, piqueux
Family: Composite or Aster Family (Compositae)
General Description: Biennial, reproducing
only by seed. It is distinguished from all other thistles by the
covering of short, sharp prickles on the upper, dark green surface
of the leaf blade, these prickles (apart from the obvious spines
along the margins and tips of the lobes) make the surface very harsh
to the touch. Its purple flower heads are larger than Canada
thistle, its involucral bracts surrounding the heads are more
slender and usually more numerous than in Nodding
thistle or Plumeless
thistle and the hairs (pappus) on its seeds are feather-like
(have plumes) rather than being straight and unbranched as in the
latter two thistles.
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![]() Bull thistle. A. Base of plant. |
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![]() C. "Seed". |
![]() D. Portion of a leaf showing its very rough, prickly surface. |
Stems & Roots: Stems erect, 30-150
cm (1-5 ft) high, rarely much taller, usually widely branched, short-hairy;
middle and upper stems of large plants with narrow, very spiny leaf-like
wings running lengthwise; on small plants the whole stem and its
branches spiny-winged, the wing drying and disappearing as the stem
gets thicker and woody leaves in a large, flat basal rosette during
the first year, each leaf deeply lobed, the lobes usually grouped
in 2's or 3's together along each side of the leaf with distinctly
unlobed portions between them, with long (about 1 cm, 2/5 in.),
hard, sharp spines from the tips of each lobe and smaller spines
along the margins; under-surface light green, finely woolly-hairy
and soft to the touch; upper surface dark green, with closely spaced,
short, sharp prickles and very prickly to the touch stem leaves
similar to rosette leaves but smaller upwards on the stem, alternate
(1 per node).
Flowers & Fruit: Flower heads
erect at tips of branches, large, 2.5-7.5 cm (1-3 in.) across, without
ray florets but with long purplish disk florets and surrounded by
an involucre of many, overlapping, very narrow, outward-pointing
green bracts, each tipped with a firm, yellowish spine; seeds about
4 mm (1/6 in.) long, grayish-brown with darker lines, shiny, the
hair (pappus) at tip of seed long and branching feather-like (plumose)
Flowers from July to September.
Habitat: Bull thistle is common throughout
Ontario in pastures, edges of woods, waste places, fence lines and
roadsides; its rosettes are occasionally troublesome in lawns and
gardens.
Related Links
... on general Weed
topics
... on weed identification, order OMAFRA
Publication 505: Ontario Weeds
... on weed control, order OMAFRA
Publication 75: Guide To Weed Control
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