Cirsium muticum Michx.
Original Published Description:
Swamp thistle, Dunce-nettle, Horsetops, Chardon mutique
Cirsium muticum was first described by Andre Michaux in Flora boreali-american :sistens caracteres plantarum quas in America septentrionali collegit et detexit Andreas Michaux in 1803. Synonyms for this species are Carduus muticus and Cirsium muticum var. monticola.
It is a biennial forb in the lineage of true thistles. It may be distinguished from other Cirsium species by the appearance of cobweb-like hairs covering its involucres, which support pink to purple flowers. Its spines are softer and significantly less dense than other species of Cirsium by comparison, and the stem is usually entirely unwinged. It prefers wet environments, as indicated by the vernacular “swamp thistle,” and will not grow in dry soil. It tends to flower later in the summer than its relatives, from July to September. It is distributed across the entirety of eastern North America. It stretches from Manitoba and Saskatchewan down to Florida, and from the Atlantic coast west to Texas, although it is more common in the northern part of its range. It is considered threatened in the state of Arkansas, where it is also classified as a weed because it is a member of Cirsium. Although some species or Cirsium are invasive weeds detrimental to farming and grazing, C. muticum is not one of them, and is being eradicated unnecessarily. It serves as a larval host and a nectar source for certain species of butterflies and moths.
The swamp thistle is listed as threatened in the state of Arkansas. (USDA, 2010.)
"Biennials, 30–230 cm; taproots fleshy. Stems single, erect, villous with septate trichomes or glabrate, distally sometimes thinly tomentose; branches few–many, ascending. Leaves ovate to broadly elliptic or obovate, 15–55 × 4–20 cm, deeply pinnatifid, to 7/8 to midribs, lobes linear to lanceolate, acute to acuminate, irregularly few toothed or lobed, main spines 2–3 mm, abaxial faces thinly tomentose or glabrate, villous with septate trichomes on the veins, adaxial faces thinly pilose; basal usually absent at flowering, petioles spiny-winged, bases tapered; principal cauline petiolate or sessile, gradually reduced distally, bases sometimes ± clasping, not decurrent; distal cauline bractlike with narrowly linear lobes, often spinier than the proximal. Heads 1–many in ± open corymbiform or paniculiform arrays. Peduncles 0–15 cm (sometimes overtopped by distal cauline leaves, not subtended by involucre-like ring of bracts. . Involucres ovoid to broadly cylindric or campanulate, 1.7–3 × 1–3 cm, arachnoid. Phyllaries in 8–12 series, strongly imbricate, dull green with darker subapical patch, ovate (outer) to linear-lanceolate (inner), abaxial faces with narrow glutinous ridge, outer and middle appressed, bodies minutely spinulose, apices obtuse to acute, spines erect (sometimes appearing as spreading in dry specimens), 0–0.5 mm; apices of inner phyllaries straight or ± flexuous, flattened. Corollas lavender or purple (white), 16–32 mm, tubes 7–15 mm, throats 4.5–10 mm (noticeably wider than tubes. , lobes 4–8 mm; style tips 3.5–5 mm. Cypselae dark brown, 4.5–5.5 mm, apical collars yellow, 0.3 mm; pappi 12–20 mm. 2n = 20, 21, 22, 23, 30."
Cirsium arvense, an invasive plant commonly known as the Canada thistle.
The most common chromosome number for C. muticum is 2n=20. Individuals with 2n=23,24 show reduced fertility. (Bloom, 1977.)
Ecology and Distribution
Cirsium muticum flowers later than other species of Cirsium, in the summer from July to September. (Keil, 2006.)
Cirsium muticum has formed natural hybrids with C. discolor and C. flodmanii. (Keil, 2006.)
The specialized cypsela usually remains attached to calyx tissue, facilitating wind dispersal. It can also be dispersed with the aid of seed-carrying birds.
Cirsium muticum has a very wide range in Northern America. It spans from the Canadian provinces of Saskatchewan, Manitoba, Ontario, Quebec, Labrador and Newfoundland down the Atlantic Coast through Northern Florida, west across the Gulf Coast to Texas, and north again with border states of Oklahoma, Missourri, Iowa, Minnesota and North Dakota. It can be found in wetlands in any state included in these boundaries. It is more densely distributed in the northern portion of its range, with scattered populations in the coastal plain. For more information, see the map provided by Flora of North America. (Keil, 2006.)
Highly organic, poorly drained soils (Ownbey, 1951.)
Cirsium muticum prefers damp habitats and wet soil. It grows in fens, marshes, woods meadows, swamps, bogs, prairies, streambanks, thickets, and open woods.
Biennial. In its first year, it produces a basal rosette of leaves. It flowers in its second year, and fruits in its senescence.
Sexual reproduction occurs with flowering in the summer (July to September) and seed formation in late summer.
All Cirsium species are listed as a noxious weed in the state of Arkansas, and a primary noxious weed in the state of Iowa. (USDA, 2010.)
Cirsium muticum is a native thistle, softer and more managable than related species of Cirsium, so it is often planted in gardens. Acting as a larval host for some rare species of butterfly, it makes a nice addition to butterfly gardens.
- Carduus glutinosus (synonym)
- Carduus muticus (Michx.) Pers. (synonym)
- Cirsium bigelowii DC. (synonym)
- Cirsium horridum (Adans.) Petr. (synonym)
- Cnicus glaber Nutt. (synonym)
- Cnicus glutinosus Bigelow (synonym)
- Cnicus muticus Elliott (synonym)