Conyza canadensis (L.) Cronquist
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Authority
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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Family
Asteraceae
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Scientific Name
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Description
Species Description - Annual or winter-annual, 1–15 dm, simple or nearly so to the infl; lvs numerous, ± pubescent, or at least coarsely ciliate at the base, oblanceolate to linear, acute, toothed (especially the lower) or entire, gradually reduced upwards, the cauline ones to 8 cm × 8 mm, the basal ones larger and broader but generally deciduous; heads, except in depauperate plants, numerous m a long and open infl; invol 3–4 mm, glabrous or with a few small scattered hairs, the bracts strongly imbricate, brown or with a brown or pale midvein and greener sides; rays mostly 25–40, commonly ca 34, white or sometimes pinkish, 0.5–1.0 mm, equaling or shortly surpassing the style and pappus; 2n=18. A weed in waste places and old fields, throughout the U.S. and s. Can. and to trop. Amer. Late summer and autumn. (Leptilon c.; Erigeron c.) Var. canadensis, our common phase, has the stem coarsely spreading-hirsute, and lacks purple tips on the bracts. Var. pusilla (Nutt.) Cronquist, chiefly along the coast or on the coastal plain, from Conn. to trop. Amer., has the stem glabrous or nearly so, and some of or all the invol bracts are minutely purple-tipped. (Leptilon p.)
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Common Names
horseweed