Ontario Weeds: Bull thistle
Excerpt from Publication 505, Ontario Weeds, Order this publication
Table of Contents
- Other Names
- General Description
- Stems and Roots
- Flowers and Fruit
- Related Links
Name: Bull thistle, Cirsium vulgare
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.
Bull thistle. A. Base of plant.
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.
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