Most people don't grow thistles as ornamentals but you have to admit the flower is nice and is very attractive to bees and butterflies. If you do let them grow near you for the beauty of the flowers, it is suggested you avoid this one unless you control seed production.
Stems: Bull Thistle plants can reach up to 2 to 6 feet in height with occasional lateral branching. Stems are light green and have dense white hair on their angular circumference. The angles appear as small wings descending from the leaf and they are very spiny. The plant is usually biennial, forming a basal rosette and taproot the first year and sending up the tall stem the second year. Stems may be single or many from the root.
Leaves: Leaves are oblong, 5 to 15 inches long, several inches across, alternate, pinnately divided into rigid triangular to lanceolate (broadest below the middle) shaped lobes which then may have teeth; each lobe has spines. The upper side is dark green with short rough white hair and bristle-like spines and the underside is light green with woolly hair. This is the only thistle in Minnesota or in North America with bristle-like spines on the upper leaf surface. The more basal leaves have winged stalks and may or may not be present at flowering time. The lower stem leaves also have winged bases. Mid and upper stem leaves gradually reduce in size, but are more deeply lobed than the basal leaves and each mid to upper stem leaf base has a pair of small dark green wings that extend downward from the point of attachment as far as the axil of the leaf below. On these wings are the spines.
The floral array consists of one to several stalked flower clusters that may be in corymb or panicle form.
Flowers: The flower heads are up to 1 1/2 inches wide and are densely filled with many small purple 5 lobed bisexual tubular disc florets. The corollas are longer than the flower tubes, the throats have 5 lobes from which the long style is exserted. The style is tightly surrounded by 5 stamens, shorter than the style. Ray florets are lacking. The flower head is bell shaped to hemispheric in shape and the outside has 10 to 12 series of phyllaries that are green in color and have sharp tips that curl outward. Phyllaries lack the central glutinous ridge of some thistles. Scattered among these phyllaries are fine hairs that look like cobwebs. Flowers have a fragrance.
Seed: The flowers mature to a dry oblong ridged cypsela, 3 to 4.5 mm long, that has attached some long whitish-brown hair (pappus) for wind dispersion. The pappus is slightly shorter than the corolla of the floret. Seeds germinate readily; most references say they are only viable for 1 to 2 years but the MN Department of Natural Resources says 10 years.
Invasive: See notes at bottom of page.
Habitat: Bull Thistle prefers full sun, adapts to a variety of soils and colonizes disturbed sites. It grows from a tap root and does not spread much vegetatively but re-seeds by wind dispersion of the seeds. The flowers provide an attraction for bees and butterflies and the seeds are liked by the American Goldfinch which also uses the cobwebby hair of the flower head (sometimes called 'thistle-down') for nest building.
Names: An older scientific name for the plant is C. lanceolatum, and prior to that Carduus vulgaris which came after Carduus lanceolatus. See Eloise Butler's notes below. The genus Cirsium is from the Greek word kirsion - for a particular thistle and has been adopted for a number of plants generally not appreciated by gardeners. The species vulgare is from the Latin meaning 'common'. The author names for the plant classification are: ‘Savi’ is for Gaetano Savi (1769-1844), Italian naturalist who published 4 important books on Italian flora including his largest - Flora Italiana in 1818. He was first to publish this species and his work was later updated by 'Ten.' who is Michele Tenore (1780-1861), Italian botanist who helped establish and became director of the Botanical Garden of Naples.
Above: The purple 5 lobed flowers have a flower head with a series of phyllaries that are green in color and have sharp tips that curl outward. Scattered among these phyllaries are fine hairs that look like cobwebs. Drawing from Flora von Deutschland.
Below: 1st & 2nd photos - Bull Thistle has a tall stem with branching usually occurring only near the top. Flower heads develop as singles or in most cases, in small open clusters. 3rd photo - The stems have dense white hair and spines on the angles formed by the leaf wings that descend downward to the axil of the next lower leaf.
Below: Several individual florets. The5 lobes of the corolla are 5 to 7 mm long. The upper floret in the photo shows the style exserted from the tube with the darker stamens surrounding it.
Below: 1st photo - In Minnesota the Bull Thistle forms a first year rosette of basal leaves and in the second year (2nd photo) sends up the stems forming the full plant.
Below: The flower heads may be single or in corymb or panicle type arrays. Each flower stalk has a small leaf-like bract. The disc florets are bisexual, many in number, and have purple corollas from which the long style is exerted.
Below: 1st photo - A stem leaf is pinnately divided into lobes which have spines. The upper surface is dark green with rough hair and bristly spines. 2nd photo - The underside of stem leaves is a lighter green and covered with dense woolly hair.
Below left: 1st photo - flower heads in various states of seed maturity. 2nd photo - The flowers mature to an oblong ridged dry cypsela that has attached some long white hair for wind dispersion.
Notes: Bull Thistle is a non-native plant that is found in the majority of Minnesota counties with most of the exceptions found in the western side of the state. In North America it is found across all the of the continent except several of the far north Canadian provinces and also Florida and the Canadian maritime provinces excepted. Eloise Butler first noted it in the Garden when she reported it blooming on Aug. 5, 1914. She used the older name of C. lanceolatum. Martha Crone, liking the plant, actually planted two in July 1945 and more in 1946 and '48.
Invasive: In nine states, including Minnesota, it is classified as a noxious weed. It is one of those ecological stowaways that made its way to North America from its home in Europe, Western Asia and Northwest Africa. Control: As this plants spreads by reseeding, it is controlled by cutting it down to the level of the plant crown before the flowers produce seed. It therefore, cannot recover from cultivation either, which eliminates if from most cultivated areas, but pastures and graze land are a different problem. Cattle will not eat it so it must be cut or spot treated with glyphosate.
While speaking primarily of the non-invasive thistles, Eloise Butler wrote: "The Scotch made no mistake in selecting the thistle for their national flower. Bristling with needle-like prickles, a type of stern independence, it does not admit of close intimacy. But we are captivated by its reddish purple blooms, fragrant as roses and brimmed with sweetness. Economical and thrifty, the thistle can wrest a living from the scantiest means; but “ower canny” as it is, it sends out myriads of plumy seeds, by which it will establish itself in richer soil whenever the opportunity offers. The voracious caterpillar crawls by it to plants with unarmed herbage; the thistle is browsed only be underfed donkeys. It is often decked with winged visitants of black and gold, the thistle birds or goldfinches, surrounded by drifting clouds of silvery plumes, as they lightly swing on the matured flower heads and eagerly break them apart to obtain their favorite food. The buds, the beautiful flower clusters, the feathery balls of fruit, and the deeply lobed leaves with ruffled margins of the thistle, all readily lend themselves to designs for ornament."
"The Field Thistle, Cirsium discolor, is particularly lovely by reason of its pale pink, or sometimes white flowers, and long, drooping leaves. The Bull Thistle [Cirsium vulgare] has larger heads and still more formidable prickles; while the tall swamp thistle is less stout and spiny. [C. muticum Michx.]. These species are not undesirable for a garden, if one has space enough to keep them at arm’s length. But no good word can be said for the Canada Thistle, an emigrant from Europe that multiplies apace, although allowed no rights of citizenship. It seems useless to legislate against it; for it has a running root stock that spreads while we sleep, and the seeds fly over the country to sow discomfort everywhere. It is a pest because it is so difficult to keep within bounds. If you wish to know just how Theophilus Thistlewaite thrust three thousand thistles through the thick of his thumb (too low an estimate by far!), clear by hand a plot of land that has been overrun by Canada Thistles." Published August 27, 1911, Minneapolis Sunday Tribune
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"