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Published In: Synopsis Generum Compositarum 203–204. 1832. (Syn. Gen. Compos.) Name publication detailView in Biodiversity Heritage Library

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 8/10/2009)


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16. Conyza Less.

Plants annual, slender or robust, with taproots, the vegetative portions glabrous or more commonly sparsely to densely hairy. Stems 1 or few to several, erect to spreading, usually much-branched either throughout or only above the midpoint, finely to coarsely angled or longitudinally lined. Basal leaves absent at flowering. Stem leaves somewhat reduced above the lower stem or relatively uniform, narrowly linear to oblong-lanceolate or oblanceolate, mostly sharply pointed at the tip, more or less tapered to a sessile or short-petiolate, often slightly expanded but nonclasping base, the margins entire or few-toothed toward the tip. Inflorescences panicles or sometimes appearing as racemes, the heads long-stalked to nearly sessile along the branches and/or in loose clusters at the branch tips, these usually with few to several minute, linear bracts. Heads appearing discoid but actually radiate (see below), not sticky or resinous. Involucre 1.5–4.0 mm long, narrowly to broadly cup-shaped or slightly bell-shaped, occasionally appearing nearly urn-shaped at flowering. Involucral bracts in 2–4 more or less unequal, overlapping series, narrowly lanceolate to linear, the tip ascending, with a slender to relatively broad, green or brown central stripe (usually with a slender, yellowish midvein), this sometimes not extending to the bract tip, and with relatively slender, thin, pale margins. Receptacle flat or nearly so, relatively smooth. Ray florets 18–40 in 1–3 series, pistillate, the corolla inconspicuous, the strap-shaped portion 0.2–0.8 mm long, sometimes reduced to a short fringe at the tip of the slender tube, white or pink to light purple, shed before fruiting. Disc florets relatively few (less than 30), perfect, the corolla 1.5–2.5 mm long, yellow, sometimes turning pinkish-tinged after the pollen has been shed, shed before fruiting. Pappus of the ray and disc florets similar, of numerous (15–25) capillary bristles, 2–3 mm long, usually white, less commonly somewhat pinkish- or yellowish-tinged. Fruits 1.0–1.5 mm long, narrowly oblong in outline (slightly tapered at the base), flattened, the angles usually with inconspicuous nerves (these occasionally appearing as narrow wings), the surface glabrous or more commonly sparsely to moderately and minutely hairy, light tan to pale grayish brown. Twenty-five to 40 species, nearly worldwide, mostly in tropical or warm-temperate regions.

Cronquist (1943) segregated Conyza from Erigeron, based primarily upon its reduced ray corollas and relatively few disc florets. Nesom (1990b) reexamined generic limits in the group and suggested some additional morphological distinctions, including that most species of Erigeron have 1-nerved (vs. 3-nerved) involucral bracts (very difficult to observe without the use of a histological clearing agent) and that, in Conyza, the pappus bristles tend to elongate slightly as the fruits mature. However, preliminary molecular studies (Noyes and Rieseberg, 1999; Noyes, 2000a) have suggested that Conyza represents a mere specialized group within the Erigeron lineage that possibly would be better resubmerged within that genus.


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1 1. Main stem solitary, erect, sparsely to densely branched above the midpoint ... 1. C. CANADENSIS

Conyza canadensis
2 1. Main stem 1 to several, spreading, sometimes ascending toward the tip, moderately to densely branched nearly throughout ... 2. C. RAMOSISSIMA Conyza ramosissima
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