Tall Thistle
Cirsium altissimum
Aster family (Asteraceae)

Description: This native wildflower is a biennial or short-lived perennial. During the 1st year, it consists of a low rosette of leaves spanning about 1' across. During the 2nd year and thereafter, it develops stems with alternate leaves and becomes about 3-8' tall. These stems are usually sparingly branched. The central stem and side stems are light green to reddish brown, terete with several longitudinal ridges, and pubescent-woolly. The alternate leaves are up to 9" long and 3" across, becoming gradually smaller as they ascend the stems. These leaves are lanceolate, oblanceolate, or elliptic in shape; their margins are entire, slightly dentate, or shallowly lobed. At the pointed tip of each lobe or dentate tooth, there is usually a spine. The upper surface of each leaf is green with appressed white hairs, while the lower surface is covered with a dense mat of white-woolly hairs. The base of each leaf is sessile or clasps its stem slightly. The basal leaves of 1st year plants are similar to the alternate leaves, except they are often more deeply pinnatifid. 

The upper stems terminate in individual flowerheads spanning about 2" across. Each flowerhead has a multitude of small disk florets that are pink to purplish pink. Each floret has a tubular corolla that divides into 5 slender lobes. The base of the flowerhead is surrounded by numerous floral scales (phyllaries) that partially overlap each other. Each small floral scale is lanceolate-ovate and dark green with a white midrib; it has a dark tip, where a fine spine projects outward. Underneath each flowerhead, there are 2-3 small leafy bracts with spines along their margins like the leaves. The blooming period occurs from late summer to early fall and lasts about 1–1 months. The flowerheads are usually fragrant. After the blooming period, the entire plant begins to wither away and turns yellow to brown. The disk florets of the flowerheads become masses of bullet-shaped achenes with tufts of cottony white hairs. These achenes are distributed by the wind. The root system consists of a taproot. This wildflower spreads by reseeding itself.

Cultivation: The preference is full sun to light shade, moist to mesic areas, and a fertile loam, clay-loam, or sandy-loam soil. Tall Thistle is more tolerant of shade than other thistles. The lower leaves may wither away prematurely at a dry sunny site. The size of this plant can vary significantly depending on environmental conditions.

Range & Habitat: Tall Thistle is occasional throughout Illinois (see Distribution Map). It is widely distributed, but usually isn't common where it occurs. Habitats include open deciduous woodlands, woodland borders, thinly wooded rocky slopes, areas along woodland paths, savannas, thickets, swamps, meadows, areas along railroads, and roadsides. Tall Thistle can be found in both disturbed and undisturbed habitats; it is found in wooded habitats more often than other thistles.

Faunal Associations: The nectar of the showy flowerheads attracts various long-tongued bees (honeybees, bumblebees, digger bees), butterflies, skippers, and Sphinx moths (including Hummingbird Clearwing moths). Long-tongued bees and smaller Halictid bees also collect pollen from the flowers. Goldfinches feed on thistle seeds and use the tufts of hair in the construction of their little nests. Various sparrows and the Slate-Colored Junco also eat thistle seeds occasionally. The caterpillars of the butterflies Vanessa cardui (Painted Lady) and Calephelis mutica (Swamp Metalmark) have been observed feeding on the foliage of Tall Thistle. The caterpillars of several moths also feed on Cirsium spp. (Thistles); see the Moth Table for a listing of these species. Other insects that feed on thistles include Oulema palustris (Leaf Beetle sp.), Cassida rubiginosa (Thistle Tortoise Beetle), Euphoria inda (Bumble Flower Beetle), and Melanoplus borealis borealis (Northern Grasshopper).

Photographic Location: Along a woodland path at Fox Ridge State Park in east-central Illinois.

Comments: As the common name suggests, this thistle can become quite tall. It resembles Cirsium discolor (Pasture Thistle) and other common thistles, except that its leaves are less pinnatifid and spiny. The native Pasture Thistle prefers habitats that are more dry and sunny, but it is also sometimes found in wooded habitats. An aggressive Eurasian species, Cirsium vulgare (Bull Thistle), also prefers habitats that are more dry and sunny; it is even more heavily armed with spines than the Pasture Thistle. Unlike the Tall Thistle and Pasture Thistle, the Bull Thistle has leaf undersides that are more green because they are less densely hairy. The leaf undersides of the preceding native thistles are bright white because they have dense mats of white-woolly hairs. All of these tall-growing thistles are in bloom at about the same time of year and their erect flowerheads are pink to purplish pink.

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