14. Cirsium Muticum Michx. Swamp Thistle

Fig. 4649

Cirsium muticum Michx. Fl. Bor. Am. 2: 89. 1803. Carduus muticus Pers. Syn. 2: 386. 1807. Cnicus muticus Pursh, Fl. Am. Sept. 506. 1814. Carduus muticus subpinnatifidus Britton, in Britt.

& Brown, III. Fl. 3: 489. 1898. Cnicus muticus alpicola Fernald, Ott. Nat. 1905:

166.

Biennial; stem woolly or villous when young, becoming glabrate, slender, striate, leafy, paniculately branched above, 3°-8° high. Leaves densely white-tomentose beneath when young, sometimes becoming glabrous on both sides, deeply pinnatifid into lanceolate or oblong, entire, lobed or dentate, spiny segments usually tipped with slender prickles, or sometimes merely lobed; basal leaves petioled, 4'-8' long, those of the stem sessile and smaller; heads about 1 1/2' broad and high, solitary, terminal, naked-peduncled, or with a few small bract-like leaves near the base; outer bracts viscid, appressed, more or less cottony, ovate or ovate-lanceolate, the inner linear-lanceolate, acute, all unarmed; flowers purple.

In swamps and moist soil, Newfoundland to Florida, Saskatchewan and Texas. July-Oct.

15. Cirsium Arvense (L.) Scop. Canada Thistle. Creeping Thistle

Fig. 4650

Serratula arvensis L. Sp. Pl. 820. 1753. Cirsium arvense Scop. Fl. Cam. Ed. 2, 2: 126. 1772. Carduus arvensis Robs. Brit. Fl. 163. 1777. Cnicus arvensis Hoffm. Deutsch. Fl. Ed. 2, 1: Part. 2, 130. 1804.

Perennial by horizontal rootstocks, forming patches, nearly glabrous, or the leaves sometimes woolly beneath; stems striate, 1°-3° high, branched above. Leaves sessile, slightly clasping, but not decurrent, lanceolate or oblong-lanceolate, deeply pinnatifid into very prickly, lobed or dentate segments, or sometimes nearly or quite entire; basal leaves sometimes petioled, 5'-8' long; heads numerous, corymbose, dioecious, 1'broad or less, nearly 1' high, purple or white, staminate heads globose, corollas projecting; pistillate heads oblong-campanulate, corollas shorter, the long pappus conspicuous; outer bracts ovate or ovate-lanceolate, appressed, tipped with short prickly points, inner bracts of the pistillate heads linear, elongated.

In fields and waste places, Newfoundland to Virginia, British Columbia, Nebraska and Utah. In many places a pernicious weed. Races differ in leaf-form and in pubescence. Naturalized from Europe. Way- or cursed thistle. Corn-, hard- or prickly-thistle. June-Sept.

16. Cirsium Palustre (L.) Scop. Marsh Thistle

Fig. 4651

Carduus palustris L. Sp. Pl. 822. 1753.

Cirsium palustre Scop. Fl. Cam. Ed. 2, 2: 128. 1772.

Annual or biennial; stem little branched, 4°-5° high, loosely floccose or glabrate and covered by the decurrent prickly margins of the leaves. Leaves pinnatifid, the lower often 6'-8' long, linear-oblong in outline, the segments lobed, loosely floccose beneath, spinulose; heads usually many, rather less than 1' broad, densely clustered, short-peduncled, the involucre ovoid, its bracts with very short, prickly tips.

Woodlands, East Andover, New Hampshire, recorded as thoroughly naturalized. Native of Europe and northern Asia. Summer.

Cirsium canum (L.) Bieb., with larger, long-peduncled heads, the decurrent leaf-bases merely ciliate, is recorded as established in Massachusetts. Adventive from Europe.