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  Asclepiadaceae: Asclepias incarnata

  R. Neil Reese

  Asclepias incarnata is a mostly solitary stemmed, upright, tall plant (70 to 200 cm) growing from a stout base and containing milky white sap. Usually, its stems have many branches toward the top. All portions of the plant contain a white milky juice. The mostly oppositely simple leaves are 5 to 15 cm long and 1 to 3 cm wide, ascending to spreading, narrow and lance-shaped, with the ends tapering to a sharp point and the margins entire. They are attached to the stem by a short petiole, 3-17 mm long. The inflorescences are terminal to the stem and branches, contain 10-40 flowers each attached by a short pedicel (10-17 mm) connected to a 1-7 cm peduncle. Flowers are 9-11 mm tall with 5-merous calyx has green to purple lobes 1.3-2.3 mm long. The petals are bright pink to rarely white, reflexed 5-6 mm long. The stamens and pistil are pink to white and fused, 1.2-1.8 mm tall and 1-1.5 mm wide. The fruit is an erect follicle 5-8 cm long. The seeds are broadly ovate 6-9 mm long and are covered with long white hairs. Swamp milkweed blooms from June through September and is commonly found in marshes, along banks of lakes, ponds and other waterways throughout South Dakota.

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  Asclepiadaceae : Asclepias pumila

  R. Neil Reese

  Asclepias pumila is a perennial herb with milky white sap, which grows from a taproot or slender rhizome with 1 to several stems arising from a branched base and reaching 8 cm to 30 cm in height. The leaves are simple, alternate in a tight spiral and often whorled near the base of the stem. The blade is narrow 1.5-6 cm long and about 1 mm wide, erect to spreading, lacks a petiole and the margin is entire. There are 1 to many inflorescences in the axils of the upper leaves, each with 4-20 flowers in an umbellate cyme. The flowers are 5-8 mm long, the calyx green to purple with 5 lobes. The corolla is white to pink tinged or sometimes a yellow green, reflexed and 2.8-4.2 mm long. The fruit are follicles that are erect, narrow cylinders 4-6 cm long and 6-8 mm wide. The seeds are ovate 4-6 mm long with long white hairs that turn brown with age. As with other milkweeds the stamens and pistils are fused, greenish-white and 0.6 to1.1 mm tall. Plains milkweed blooms from July to September in prairies and along hillsides throughout South Dakota.

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  Asclepiadaceae: Asclepias speciosa

  R. Neil Reese

  Asclepias speciosa is a perennial herb with milky white sap, growing from a deep rhizome with solitary stems that are simple or occasionally branched, growing 50 to 100 cm in height and densely covered in hairs toward the top. The simple leaves are usually opposite with a short petiole 2-13 mm in length. The blades are entire, broadly lanceolate to ovate. 8-20 cm long and 2.5-10 cm wide, with a thick covering of hairs on the underside. The inflorescences are few to several in the upper leaf axils, each coming from a 2-10 cm peduncle 1-3 cm long hat are having 10 to 40 flowers attached by a 1-3 cm long pedicel that is covered with short hairs. The flowers are 15-28 mm long, the calyx is green to purple, covered with hairs and with 5 lobes that are 5-7 mm long. The purple to rose colored corolla lobes are rounded, reflexed and 9-15 mm long the apex is attenuated looking like a crown. The fused stamens and pistil os pale rose to pinkish-cream colored, broadly obconic 1-1.5 mm tall a\nd 2.5-3.3 mm wide. The fruit are erect follicles that are 7-11 cm long and 2-3 cm wide. The sees are ovate 6-9 mm long with long white to brownish hairs. Showy milkweed blooms from May through August on the banks of lakes, ponds and streams or moist areas on prairies throughout much of South Dakota. Showy milkweed and common milkweed are very similar. They can be distinguished by their flower petals, with A. speciosa having longer narrower petal lobes that give the flower the appearance of a crown.

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  Asclepiadaceae: Asclepias syriaca

  R. Neil Reese

  Asclepias syriaca is a perennial herb with milky white sap, growing from a deep rhizome with solitary stems that are simple or occasionally branched, growing 0.6 to 2 m in height and densely covered in hairs toward the top. The simple leaves are usually opposite with a short petiole 2-13 mm in length. The blades are broadly lanceolate to ovate. 6-30 cm long and 5-11 cm wide, margins entire, with a thick covering of hairs on the underside. The inflorescences are few to several in the upper leaf axils, each coming from a 1-14 cm peduncle 1.5-4.5 cm long that have 20 to130 flowers attached by 1-3 cm long pedicels that are covered with short hairs. The flowers are 11-17 mm long, the calyx is green to purple, covered with hairs and with 5 lobes that are 2.4-4 mm long. The purple to rose to rarely white colored corolla lobes are rounded, reflexed and 9-15 mm long the apex is attenuated looking like a crown. The fused stamens and pistil os pale rose to pinkish-cream colored, broadly obconic 1-1.9 mm tall and 1.5-2.5 mm wide. The fruit are erect follicles that are 7-11 cm long and 2-3.5 cm wide. The seeds are ovate 6-8 mm long with long white to brownish hairs. Common milkweed blooms from May through August on the banks of lakes, ponds and streams or moist areas on prairies and along roadsides throughout much of South Dakota. Showy milkweed and common milkweed are very similar. They can be distinguished by their flower petals, with A. speciosa having longer narrower petal lobes that give the flower the appearance of a crown.

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  Asclepiadaceae : Asclepias tuberosa

  R. Neil Reese

  Asclepias tuberosa is a perennial herb with milky white sap, growing from a deep rootstock with 1 to many stems arising from thick crown. The stems are simple to having a few branches toward the top, generally covered with short hairs, and reaching 30 to 90 cm in height. The ascending to spreading simple leaves are alternate on the lower stem but become subopposite to opposite where the flowers emerge. The blades are entire, linear to broadly lanceolate, 5-10 cm long and 7-23 mm wide with margins that curl downward. There are 1 to several umbellate clusters of flowers at the ends of the stem and branches and in the upper leaf axils. Six to 25 flowers are attached to a short peduncle (< 3 cm long) or sessile with each flower having a short (12-19mm) pedicel. Flowers are 11-16 mm long, the calyx is covered with hairs and green to purplish colored, with lobes 2-4 mm long. The bright orange to reddish corolla lobes are reflexed and 5.5-8.5 mm long. The fused stamens and pistil is about 1-1.5 mm tall and wide. The fruit are tapered at both ends, 8-15 cm long and 1-1.5 cm wide. The seeds are oval 5-7 mm long with long white hairs. Butterfly milkweed blooms from May to August in sandy prairies and open woodlands in a few counties in both eastern and western South Dakota.

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  Asclepiadaceae : Asclepias verticillata

  R. Neil Reese

  Asclepias verticillata is a perennial herb containing milky white sap, with 1 to a few stems arising from a fibrous crown, occasionally branched and 35-90 cm tall. The sessile leaves are whorled with 3-6 leaves per node. The blades are entire, linear, 1.5 to 8 cm long and about 1 mm wide. The inflorescences are few to many in the axils of the upper leaves, each containing 6-20 flowers. Flower buds appear yellowish but produce white to greenish white flowers. Each flower is attached to a short peduncle (1-4 cm long) by a 5-11 mm pedicel. Calyx lobes are green to purple tinged 1-2.5 mm long and the corolla lobes are white to greenish white, reflexed and3.5-4.5 mm long. The fruit are erect follicles 8-10.5 cm long and < 1 cm wide. The ovate seeds are 5-6 mm long with long white hairs. Whorled milkweed blooms from June through September in the prairies, flood plains and open woods of South Dakota.

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  Asclepiadaceae: Asclepias viridiflora

  R Neil Reese

  Asclepias viridiflora is a perennial herb, with milky white sap, having 1 or 2 stems growing from a taproot, with the stems only occasionally branched, stout and 10 to 60 cm tall. The simple leaves are opposite, or nearly so, to alternate. The blades are entire, variable in shape from linear to almost round, ascending to widely spreading, 4-14 cm long and 1-6 cm wide and having a few to a dense covering of whitish short woolly hairs. There are 1 to many inflorescences scattered in the axils of the leaves of the upper half of the stem. Each umbellate cluster contains 20-80 flowers, each with a short (5-15 mm) pedicel attached to a 2-20 mm peduncle. The flowers are 9.5-12.5 mm long with a green to purple tinged calyx with lobes 2-3 mm long. The corolla is pale green, with reflexed lobes 5.7-7 mm long. The fused stamens and pistil is also pale green and 1.2-1.5 mm tall and 1.2 -1.4 mm wide. The fruit is a follicle, swollen in the middle and tapered at both ends, 7-15 cm long and about 2 cm in the widest section. The seeds are obovate, 6-7.5 mm long with long tan hairs attached. Flowering occurs from June through August. Green milkweed grows on sandy to rocky soils in prairies throughout much of South Dakota.

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  Asteraceae: Achillea millefolium

  R. Neil Reese

  Achillea millefolium is a rhizomatous perennial herb which grows 30 cm to 100 cm in height. The leaves are alternate, compound bipinnately dissected, 5-20 cm long and feathery in appearance. Flowers are arranged in heads that are usually collected into flat-topped clusters. Heads are surrounded by imbricate bracts in several series and contain 10 or less ray flowers and 10-25 disk florets. Petals are white to cream-colored or rarely pinkish and bloom from May to June (later in higher locations). Fruit are flattened achenes that lack a pappus. This species is commonly found on all northern continents in mildly disturbed areas, meadows, woods, and prairies. It is common throughout South Dakota

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  Asteraceae : Ageratina altissima

  R. Neil Reese

  Ageratina altissima is a perennial herb arising from a rhizome, with upright or sometimes ascending stems, covered with short spreading hair, growing from 30 to 150 cm tall. The simple, opposite petiolate leaves have blades that are ovate to broadly ovate, contracted at the base and pointed at the tip, 6-15 cm long and 3-12 cm wide toward the base and smaller toward the top, with variously toothed margins. Each pair of leaves is positioned at a 90-degree angle from the pair above and below. The inflorescence is made up of flat-topped clusters of heads. Each head has a 3-5 mm involucre of bracts that are all about the same length. There are 12-24 white disk flowers that produce 5-sided achenes that have a bristly pappus and, when mature, appear as fluffy white balls like dandelions and seeds are carried in the wind. White snakeroot blooms in August through October in open woods and disturbed sites in eastern and south-central parts of South Dakota.

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  Asteraceae : Agoseris glauca

  R Neil Reese

  Agoseris glauca is a perennial herb having a large taproot and can grow from 8–50 cm tall. It has linear to oblanceolate leaves, 3–35 cm long, the margins are entire or with 1 to 3 pairs of shallow lobes. Stems and leaves are glabrous to sparsely villous. Flowers appear in a terminal head on a long scape with an involucre that is 1–2 cm long; phyllaries linear-lanceolate to lanceolate, in 2 to 3 indistinct series, green, glabrous to villous, sometimes glandular, often darkened along the midvein. Heads contain 15 to 150 flowers that are all ligulate, yellow, the ligules 6–22 mm long and each floret having a pappus 8–18 mm long. The fruit is an achene, with a body that is 4–9 mm long with a beak ranging from 0.5–3 mm long.

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  Asteraceae : Ambrosia trifida

  R Neil Reese

  Ambrosia trifida is an annual herb growing up to 2 m tall, but may reach over 6 m in rich, moist soils. The stem has a woody base and are branched or unbranched. Leaves are mostly oppositely arranged, with blades that are variable in shape, usually palmately lobed, and often with toothed edges. The largest leaves can be over 25 cm long and 20 cm wide, with petioles several centimeters long. They are glandular and rough in texture. The flowers are arranged in a spike, monoecious, with plants bearing inflorescences containing both pistillate and staminate flowers. Staminate flowers are yellow to greenish with no petals, about 3mm across, hanging down on short stalks along the spike. Pistillate flowers are indistinct, hidden in clusters of short leafy bracts. The fruit is a bur a few millimeters long tipped with several tiny spines.

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  Asteraceae : Anaphalis margaritacea

  R. Neil Reese

  Anaphalis margaritacea is a rhizomatous dioecious perennial herb that often grows in large patches. The stems are simple, covered with white wooly hairs, and grow from 20 to 60 cm tall. The alternate leaves are linear to linear-lanceolate, 4-9 cm long and sessile and often clasping at the base. The tops of the leaves are green, and the lower side covered with white hairs. The lower-most leaves usually withered or lacking at the time of flowering. The heads appear in July and August in flat-topped to rounded clusters. The heads have several series of imbricate involucral bracts that appear pearly-white, the involucre 5-8 mm tall and woolly at the base. The heads of male plants have numerous yellow, tubular, staminate flowers. The female plants with numerous yellow, pistillate tubular, flowers with a few functional staminate flowers. The fruits are achene-like and mature in the fall.

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  Asteraceae Antennaria howellii

  R. Neil Reese

  Antennaria howellii is a perennial herb in the Asteraceae family. It forms low mats or small tufts from a fibrous, sometimes shallow rhizomatous root system, allowing for asexual reproduction and slow vegetative spread. The stems are generally simple, erect, and slender, ranging from 5–25 cm in height, and are covered with fine, woolly hairs (notable pubescence). Basal leaves are spatulate to oblong, 1–6 cm long and 3–10 mm wide, with entire margins, a gray-green upper surface, and a densely white, woolly underside. Cauline leaves are much smaller, linear to narrowly lanceolate, and often reduced in size up the stem. Antennaria howellii is dioecious, with male and female flowers on separate plants. Flowering occurs from May to July. Numerous small, compact flower heads are arranged in clustered inflorescences with usually 2–8 terminal, discoid flower heads. The involucre is composed of several series of overlapping bracts (phyllaries) that are dry, papery, and white to pale brown with a silky texture, forming a rounded, bell-shaped structure around the flower base, giving the flower clusters a “pussytoe” appearance. The florets are small, tubular, usually white to pale pink or cream. Stamens are present in male florets with slender filaments and anthers; female florets have a pistil with a bifurcated style. The fruit is a small achene about 1 to 2 millimeters long, topped with a pappus of white, silky hairs that aid in wind dispersal. Seeds mature in mid to late summer. Howell’s pussytoes is native to South Dakota, occurring in dry prairies, open woodlands, rocky bluffs, and sandy soils, and is distributed statewide but is more common in western and northern regions.

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  Asteraceae : Antennaria neglecta

  R. Neil Reese

  Antennaria neglecta is a perennial stoloniferous herb that forms mats of dioecious colonies. The basal and stolon leaves are 1-nerved, green above with white hairs covering the lower side, 1-3 cm long and less than 1.5 cm wide. The erect flowering male or female plants have stems that are 6-25 cm tall and covered with white hairs, having thin leaves tipped by a flat, often curled appendage. The heads are usually clustered in dense capitate to open cymes and have narrow involucral bracts, 5-7 mm long, the outer bracts are brown below and scarious white above. The pappus is longer than the stigmas in female plants. The achenes are slightly tapered at the ends and 1.2-1,5 mm long. Field pussytoes blooms from March through June in pastures, prairies and open woodlands throughout South Dakota.

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  Asteraceae: Antennaria parvifolia

  R. Neil Reese

  Antennaria parvifolia is a perennial herb in the Asteraceae family. It grows from a fibrous root system and spreads asexually by slender, above-ground stolons, often forming low, dense mats. Stems are simple, unbranched, and erect to ascending, typically 5–20 cm tall, and are densely covered with soft, woolly hairs (notable pubescence). Basal leaves are numerous, forming a rosette; they are oblanceolate to spatulate, usually 1–4 cm long and 2–7 mm wide, with entire margins, a green upper surface, and a grayish, woolly underside. Cauline leaves are few, much smaller, linear to narrowly lanceolate, and reduced up the stem. This species is dioecious, with male and female flower heads on separate plants. Flowering occurs from May to July. Inflorescences are clusters of 2–7 terminal flower heads, each about 5–8 mm across. Male heads have creamy white, tubular florets with conspicuous anthers; female heads have white, hairlike pistillate florets. The involucre bracts are white or tinged with pink, giving the flower clusters a soft, “pussytoe” appearance. The fruit is a tiny, one-seeded achene (about 1 mm long) with a tuft of white pappus bristles for wind dispersal, maturing in early to midsummer. Small-leaf pussytoes is native to South Dakota, found in dry prairies, grasslands, open pine woods, and rocky or sandy sites, and is widespread but more abundant in western and central parts of the state.

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  Asteraceae : Arnica cordifolia

  R Neil Reese

  Arnica cordifolia is a perennial herb arising from long, creeping rhizomes, growing to 60 cm tall. It has two to four sets of opposite leaves on the flowering stem, each having a long petiole. Basal leaves are cordate, with long petioles and dentate margins. The cauline leaves are heart-shaped to arrowhead-shaped, with finely dentate margins. Leaf blades are 4-12 cm long and 2-9 cm wide. The inflorescence is composed of a single or occasionally 2-3 turbinate to campanulate heads, each 5–9 cm wide. The involucral bracts are 1-2 cm long, covered with white-hairs and sometimes studded with resin glands. Each head has 10-15 ray flowers with ligules 15-30 mm long and the center of each head contains several golden yellow disc florets. The achenes are 6-9 mm long with short hairs and/or glands. The pappus has long white barbed hairs. The flowers usually bloom from May through August. Heartleaf arnica grows in western South Dakota.

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  Asteraceae : Artemisia absinthium

  R Neil Reese

  Artemisia absinthium is a perennial herb to weak shrub, very fragrant, growing 40-120 cm tall, with the stems greenish with grooves and covered in short white hairs. The silvery leaves have long petioles and are spirally arranged, greenish gray above, white below, covered with silvery-white hairs, and minute oil-producing glands. The basal leaves are up to 25 cm long, bi- to tripinnate and the cauline leaves are smaller, 5–10 cm long, less divided, and with shorter petioles. The uppermost leaves may be much reduced becoming simple and sessile. The inflorescence is a diffuse panicle of heads with each head having involucral bracts 2-3 mm long and the receptacle is covered with numerous long hairs interspersed with the florets. The outer disk flowers are female and the inner florets are perfect. The achenes are cylindrical. Wormwood is an introduced species from Eurasia but is naturalized throughout the northern half of North America. It is found in open fields and along roadsides in many locations in South Dakota.

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  Asteraceae : Artemisia cana

  R Neil Reese

  Artemisia cana is perennial aromatic shrub mostly growing to < 1 m tall, but occasionally taller. The older stems become twisted with exfoliating bark and the younger stems are greenish, covered with grayish hairs. The lanceolate leaves are narrow, ranging from 2-9 cm in length, not often more than 5 mm wide, have a silvery gray pubescence and are retained year-round. The inflorescence is a series of spike-like, leafy panicles of small heads. The involucre is 4-5 mm long and has a naked receptacle. The several tiny disk flowers are all perfect producing small dark achenes. Silver sagebrush bloom in August and September and can be found in both east and west river South Dakota.

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  Asteraceae : Artemisia dracunculus

  R Neil Reese

  Artemisia dracunculus is a woody, perennial shrub, often quite fragrant, with stems ranging from 40 to 150 cm tall. The stems arise from thick, horizontal rhizomes growing singly or in clusters. The stems are often reddish colored and smooth to pubescent. Leaves are alternate, linear, 2 to 8 cm long and 1 to 6 mm wide. Basal leaves are cleft with 1 to 3 lobes. The inflorescence is a panicle with numerous heads. Each head is surrounded by an involucre that is 2-3 mm tall and has a naked receptacle. The yellow outer florets are pistillate and fertile. The central flowers are yellow, sterile, with ovaries that are abortive. The fruits are achenes elliptical and about 1.5 mm in length. Wild tarragon blooms in August and September and is usually found on dry open slopes throughout South Dakota.

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  Asteraceae : Artemisia frigida

  R Neil Reese

  Artemisia frigida is a low, spreading sub-shrub arising from a woody crown, growing from 10 to 40 cm tall. The plant has a fragrant scent, and the stems and leaves appear whitish to gray because of the dense covering of appressed hairs. Numerous leaves are clustered toward the base and scattered along the stems. The lower leaves are petiolate with blades that are up to 12 mm long, often divided several times with the segments about 1 mm wide. The upper leaves become sessile and reduced in size. The inflorescence varies from an open panicle to a raceme of small heads, each with an involucre of bracts 2-3 mm tall. The receptacle has many long hairs between the numerous small yellow flowers. The outer florets are pistilate and the central ones are perfect. Both produce small achenes. Prairie Sagewort blooms from early summer until very late in the fall. This species is common on open plains, throughout much of South Dakota.

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  Asteraceae : Artemisia ludoviciana

  R Neil Reese

  Artemisia ludoviciana is an aromatic, rhizomatous perennial herb that grows from 30-100 cm tall, covered in white hairs. The alternate, linear to lanceolate leaves are 3-11 cm long and up to 1.5 cm wide and are also covered in woolly gray or white hairs. The margins of the leaves are entire to irregularly lobed. The inflorescences are terminal narrow panicles of many nodding flower heads. Each small head is about 0.5 cm wide, surrounded by hairy involucral bracts 2.5-4 mm long. The receptacle is naked with numerous small yellow florets, the outer ones pistilate and the central florets are perfect. The fruit is a minute achene. Flowers bloom from July to October in most counties in South Dakota.

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  Asteraceae : Artemisia tridentata

  R. Neil Reese

  Artemisia tridentata is an erect, branching, aromatic, evergreen shrub, having both a deep taproot and a broad shallow root system, and growing from 0.5 to 3 m in height. The older stems are dark colored and are often gnarled with exfoliating bark. The younger branches are covered with a short pubescence. The leaves are wedge shaped, narrow at the base and tridentate at the tip. The inflorescence is a loose panicle of near sessile heads. The heads have involucral bracts 2-4 mm long and covered in whitish hairs. The several yellow florets are attached to a naked receptacle and are all perfect. The leaves contain camphor and other essential oils. The achenes are small and very dark when mature. Flowering occurs from June into September. Big sage is found on open dry plains and hills in western South Dakota.

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  Asteraceae: Balsamorhiza sagittata

  R Neil Reese

  Balsamorhiza sagittata is a perennial herb growing from a deep taproot with stems arising from a branching crown and reaching 80 cm in height. The foliage is covered with silvery hairs, often making the plant appear and feel velvety. The silvery-gray simple basal leaves are petiolate, arrowhead shaped, with blades 20-40 cm long and the margins are entire. The cauline leaves are linear to narrowly oval in shape, smaller and coated in fine to rough hairs, especially on the undersides. The inflorescence consists of one or more heads, usually solitary on each stem. Each head is surrounded by an involucre of 2-4 series of bracts and the receptacle is broadly convex. There are 13-25 yellow ray flowers with ligules 2-4 cm long surrounding a center with many yellow disk flowers. The fruit is a roughly four-sided achene, 7-8 mm long lacking a pappus. Arrowhead balsamroot blooms from May to July on open hillsides and in valleys of western South Dakota.

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  Asteraceae: Bidens vulgata

  R. Neil Reese

  Bidens vulgata is an annual herb with a fibrous root system, reproducing exclusively by seed. The stems are erect, branched above, and can reach 30–120 cm tall, often with angled or ridged surfaces and sometimes rough to the touch. Leaves are opposite, pinnately compound with 3 to 7 lance-shaped leaflets; leaflets are 3–10 cm long, with serrated margins and pointed tips, the central leaflet usually the largest. Petioles are 1 to 5 centimeters long. Both stem and leaf surfaces may be sparsely to moderately hairy. Flowering occurs from late summer to fall. The inflorescence is a loose or clustered array of small, yellow, daisy-like flower heads, each with a few inconspicuous yellow ray florets (sometimes absent) and numerous yellow disc florets. The involucral bracts are green, narrow, and often extend beyond the flower head. Flowers have five lobes; stamens number five with anthers fused into a tube around the ovary. The pistil comprises a single ovary with a bifid style. Fruits are flattened, two- to four-awned achenes ("sticktights") 4–8 mm long, brown to black at maturity, with barbed awns that easily attach to fur or clothing for dispersal. Tall Beggarticks is native to South Dakota and typically found in moist, disturbed soils such as ditches, streambanks, floodplains, wet meadows, and along roadsides, most common in the eastern and central portions of the state.

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  Asteraceae: Carduus nutans

  R. Neil Reese

  Carduus nutans is a biennial (sometimes annual or short-lived perennial) herb in the Asteraceae family. It develops from a stout, fleshy taproot and does not reproduce asexually via stolons or rhizomes. During its first year, it forms a large basal rosette of spiny, deeply lobed leaves, each up to 40 cm long, with white, woolly undersides and sharp, yellowish spines along the margins. In its second year, it produces a single, stout, erect, and often branched stem, usually 60–200 cm tall, with conspicuous wings (spiny extensions) running down from the leaf bases. Leaves are alternate and deeply lobed with spiny margins; basal and lower leaves can be 10 to 30 centimeters long and 5 to 10 centimeters wide, narrowing upward on the stem. Petioles are winged and spiny-edged. Stems and leaves are covered with cobwebby hairs, especially when young. Flowering occurs from June to September. Inflorescences are solitary or in small clusters at the stem tips; each is a large, pendulous (nodding) flower head, 3–7 cm across. The involucre consists of several series of broad, rigid, spiny-tipped green bracts (phyllaries) about 2 to 3.5 centimeters long and 0.5 to 1 centimeter wide, forming a spiny protective cup around the flower head base. Each flower head contains numerous tubular florets with 15 to 25 bright purple to pink ligulate corollas, each ligule approximately 1.5 to 2.5 centimeters long and 3 to 5 millimeters wide. Florets have five lobes; stamens number five with anthers fused around the ovary. The pistil consists of a single ovary with a two-branched style. The fruit is a small, ribbed achene about 4 to 5 millimeters long topped with a pappus of fine hairs facilitating wind dispersal. Fruits mature late summer into fall. Musk thistle is an introduced species in South Dakota, most common in disturbed sites, roadsides, pastures, fields, and rangelands, and is found statewide but especially abundant in the east and central regions.