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(Last Modified On 6/6/2013)
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(Last Modified On 6/6/2013)
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Species
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Conyza canadensis (L.) Cronq.
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PlaceOfPublication
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Bull. Torrey Bot. Club 70: 632. 1943.
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Synonym
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Erigeron canadensis L., Sp. P1. 863. 1753. TYPE: Herb. Linn. 994.10 (LINN, not seen).
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Description
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Coarse erect, sparingly branched ephemeral herb to 1.5 m tall; stems striate, glabrous to puberulent. Leaves to 10 cm long, linear or linear-lanceolate, sessile, entire or sparingly toothed, apically acute or acuminate, membranaceous, glabrous or sparingly pubescent on both sides, the midvein prominent and the minor venation obscure. Inflorescence a many-flowered open terminal panicle, much branched; bracts scattered, rarely to 15 mm long; pedicels slender, to 10 mm long. Heads small, disciform with many florets; involucral bracts imbricate in 2-3 unequal series, 3-4.5 mm long, mostly thin and glabrous; receptacle flat or slightly convex, 1-1.5 mm across, muricate; outer florets numerous, white, capillary, 2.5-3 mm long with a definite, short ( 0.7 mm) ligule; inner florets few, corolla, yellowish; slender, clearly differentiated about halfway up into a slender, cylin- drical limb, sparingly pubescent or glabrous, the lobes deltoid-acuminate, the anthers ca. 0.5 mm long, basally obtuse and with obtuse appendages, the style branches flattened with short-deltoid appendages, thickened at the margins, glandular-verrucose dorsally and glandular pilose at the junction of branch and appendage. Achene compressed, the margins slightly thickened by two prominent veins, glabrous or pubescent, especially near base and apex; pappus of fine strigulose bristles in 1 series reaching or somewhat exceeding the inner florets.
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Habit
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herb
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Note
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This species is sometimes difficult to distinguish from C. bonariensis. It is distinct in its smaller heads, more glabrate, linear foliage, glabrous or glabrate involucral bracts, and in the presence of a definite, if small, ligule on the outer florets. Plants smaller than usual with purplish-tipped involucral bracts have been recognized as var. pusillus (Nutt.) Cronq. This variety is common in the south- eastern United States and includes the majority of Panamanian specimens of C. canadensis.
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Distribution
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nearly cosmopolitan in distribution but is perhaps more plentiful in temperate regions. In Panama it is found in weedy areas in upland Chiriqui. Plants from Europe tend to have more prominently ciliate leaves.
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Common
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Pascueta Orozuz
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Common
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Horseweed
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Specimen
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CHIRIQUI: Escuela San Benito, Volcan, Croat 10413 (MO). Near El Hato del Volcaln, Croat 10711 (MO). Near Methodist camp near Nueva Suissa, Croat 13528 (MO). Between Boquete & Monte Rey, Croat 15805 (MO). Boquete, D'Arcy & D'Arcy 6348 (MO). Potrero, Boquete, 3800 ft, Davidson 663 (MO, US). Valley of Rio Chiriqui Viejo, N of El Hato de Volcan, 5200-5600 ft, Duke 9038 (MO). Near Volcan, 4600 ft, Duke 9136 (MO). Near Boquete, 3300-4200 ft, Lewis et al. 583 (MO, US). Nueva California, W of Volcaln, Tyson 6674 (MO).
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