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186. Erigeron Linnaeus, Sp. Pl. 2: 863. 1753; Gen. Pl. ed. 5, 371. 1754.

Fleabane, érigéron, vergerette [Greek eri, early, or erio, woolly, and geron, old man, perhaps alluding to pappus, which becomes gray and accrescent in some species, or to solitary, woolly heads of some of species]

Guy L. Nesom

Achaetogeron A. Gray; Trimorpha Cassini

Annuals, biennials, or perennials [subshrubs, shrubs, trees], (0.5–)2–90(–100) cm (taprooted, fibrous-rooted, or rhizomatous and fibrous-rooted, sometimes with simple or branched caudices, sometimes stoloniferous). Stems erect to ascending, decumbent, or prostrate, simple or branched, glabrous or hairy, sometimes glandular (hairs 2-seriate, minute, sometimes stipitate). Leaves basal and/or cauline (basal persistent or not to flowering); alternate; sessile or petiolate; blades 1-nerved (3-nerved), linear to lanceolate, oblanceolate, or spatulate (bases sometimes clasping), margins entire or ± dentate to pinnatifid, faces glabrous or hairy, sometimes glandular. Heads usually radiate, sometimes discoid or disciform (erect, nodding, or arching-pendent in bud), borne singly or in loose, corymbiform or paniculiform arrays. Involucres turbinate to hemispheric, 5–35 mm diam. Phyllaries 30–125(–150) in 2–5 series, 1- or 3-nerved (nerves golden-resinous; usually flat, rarely broadly keeled to convex), narrowly elliptic- to linear-lanceolate, unequal to equal, margins scarious or not, faces hairy or glabrous, sometimes glandular. Receptacles flat to conic, pitted, epaleate. Ray florets 0 or 12–350 in 1(–2+) series, pistillate, fertile; corollas usually white to bluish or purplish to pink, less commonly yellow (coiling from apices, reflexing at tube/lamina junction, or remaining ± straight and spreading). Peripheral florets (disciform heads) 50–200 in 1–4 series, pistillate. Disc florets 25–450, bisexual, fertile; corollas yellow (nerves orange-resinous), tubes shorter than usually tubular, sometimes strongly inflated and indurate throats, lobes 5, erect to spreading, deltate; style-branch appendages mostly deltate (papillate). Cypselae (tan) oblong to oblong-obovoid, compressed to flattened, 2(–4)-nerved, or subterete, 5–14-nerved (sect. Wyomingia and some other species), faces glabrous or strigose or sericeous, eglandular; pappi persistent or readily falling, usually of outer setae or scales (0.1–0.4 mm), sometimes connate, plus 5–40(–50), stramineous, barbellate bristles, sometimes pappi only on ray or only on disc cypselae, or 0. x = 9.

Species ca. 390 (173 in the flora): nearly worldwide, mostly in temperate regions.

The North American and Central American species of Erigeron have been divided into sections (G. L. Nesom 1989c, 1990g, 1994b; Nesom and R. D. Noyes 1999), emphasizing variation in habit (especially taprooted versus rhizomatous and fibrous-rooted), vestiture, arrangement of heads in arrays and orientation before flowering (erect, nodding, or arching-pendent), behavior of ray corolla laminae (straight, reflexing, or coiling), cypsela and pappus morphology, and other morphologic features. The sequence and groupings of species treated here reflect significant modifications of earlier arrangements.

G. L. Nesom (1989d) hypothesized that Trimorpha [Erigeron sect. Trimorpha (Cassini) de Candolle] is separate from Erigeron, more closely related to Conyza. Studies by W. Huber and colleagues (e.g., Huber 1993; Huber and Ö. Nilsson 1995) and R. D. Noyes (2000) have shown that Trimorpha species are closely related to those of sect. Erigeron and that both sections are relatively recently derived within the genus. As suggested by Nesom (1994b) and by Huber and Nilsson, and as discussed in detail and experimentally confirmed by Noyes, autogamous breeding systems apparently have arisen independently in groups of Astereae, including Trimorpha and Conyza, where the pistillate florets of a head are greatly increased in number (often outnumbering the bisexual florets), in multiple series, the inner sometimes with filiform, elaminate corollas, and the outer with reduced laminae.

In the molecular analysis by R. D. Noyes (2000), Conyzinae comprises Erigeron, American Conyza, the four genera of the South American Leptostelma group, and the North American Aphanostephus; the cladistically basal and terminal taxa of the subtribe are members of Erigeron. Noyes (p. 107) observed that "strictly speaking, although the Conyzinae form a monophyletic group [with caveats regarding Old World Conyza], Erigeron is paraphyletic, as five other genera are derived from within it." The molecular study included 46 of the 173 species treated here.

Polyploidy is common among species of Erigeron, and agamospermy apparently is a common correlate of polyploidy, especially in odd-polyploid plants. Molecular phylogenetic data (R. D. Noyes 2000) indicate that agamospermy has arisen at least three times within the genus.

In the descriptions and keys, some characteristics are assumed constant unless otherwise indicated (usually in parentheses); particular application of terms is discussed here. The indumentum of erigerons is often complex; in order to simplify descriptions, glabrous applies here only to absence of non-glandular hairs, eglandular to the absence of glandular hairs; a totally glabrous plant (in the usual sense) would be glabrous and eglandular. Petiole margins are eciliate or sparsely ciliate unless otherwise indicated. Leaf bases of most erigerons are broadened or not, not thickened and white-indurate. Margins of leaves in some erigerons are entire but for tiny callous enations that correspond to the callous tips of teeth on some leaves with serrate margins. Here, margins with such tiny enations are described as denticulate. Heads of some erigerons are "pseudodisciform" in the sense that the outer pistillate florets have relatively small, ± filiform laminae (such florets are technically "ray florets" even though their "rays" are inconspicuous) and the inner pistillate florets have no laminae on their corollas. The distinction between corollas without and those with laminae is sometimes arbitrary. Ray laminae are considered strap-shaped and spreading unless otherwise indicated. Descriptions of ray color as "blue" should be read as lavender-blue.

Artificial distinctions are used in the key to groups of species recognized by leafy runners, pinnately lobed or dissected leaves, discoid or disciform heads, and yellow rays. Otherwise, species tend to be identified within natural groups. Couplets that use basal parts for distinction or inference of duration may be difficult if collections lack diagnostic basal parts or if the nature of the basal parts is not clear. Yet, these differences are significant in delimiting species groups and often critical in identification, and the pertinent species otherwise would be scattered widely in a more artificial key.


Cronquist, A. 1947. A revision of the North American species of Erigeron, north of Mexico. Brittonia 6: 121–302. Nesom, G. L. 1989c. Infrageneric taxonomy of New World Erigeron (Compositae: Astereae). Phytologia 67: 67–93. Nesom, G. L. 1989d. The separation of Trimorpha (Compositae: Astereae) from Erigeron. Phytologia 67: 61–66. Nesom, G. L. 1990g. Taxonomy of the Erigeron coronarius group of Erigeron sect. Geniculactis (Asteraceae: Astereae). Phytologia 69: 237–253. Nesom, G. L. 2004e. Taxonomic reevaluations in North American Erigeron (Asteraceae: Astereae). Sida 21: 19–40. Nesom, G. L. and R. D. Noyes. 1999. Notes on sectional delimitations in Erigeron (Asteraceae: Astereae). Sida 18: 1161–1165.

Group 18

1 Stems and leaves glabrous, minutely glandular; basal leaves usually 3-nerved (sometimes with conspicuously raised primary and secondary venation), cauline little reduced   84 Erigeron nauseosus
+ Stems and leaves glabrous or sparsely and inconspicuously strigose (sparsely villosulous distally in E. evermannii), eglandular; basal leaves 1-nerved (never with raised venation), cauline reduced distally or essentially absent.   (2)
2 (1) Caudices with diffuse system of relatively long, slender, rhizomelike branches or basal offsets; taproots usually not evident; ray laminae reflexing   (3)
+ Caudices multicipital or with relatively long, thick to relatively slender, lignescent branches; taproots usually evident; ray laminae not reflexing (except in E. kachinensis)   (4)
3 (2) Leaves basal and reduced cauline, 15–70 × 2–11(–15) mm; phyllaries in 2–3 series   83 Erigeron leiomerus (in part)
+ Leaves all basal, 5–12 × 1–3.5 mm; phyllaries in 3–4(–5) series   86 Erigeron scopulinus (in part)
4 (2) Phyllaries glabrous; caudex branches relatively short and thick; rays purplish to lavender; New Mexico   80 Erigeron subglaber
+ Phyllaries minutely glandular, or sparsely to moderately hirsuto-villous to strigose, or both hairy and glandular; caudex branches short and thick to long and slender; rays mostly white to pink; n to w of New Mexico   (5)
5 (4) Phyllaries eglandular or sparsely glandular; ray laminae reflexing; cypselae 1.2–1.6 mm; Arizona   (6)
+ Phyllaries minutely glandular; ray laminae reflexing or not; cypselae 1.5–3.5 mm; n to ne of Arizona   (9)
6 (5) Leaves usually apically 3-lobed to pinnatifid with 2–3(–5) pairs of lobes; ray laminae sometimes with abaxial lilac midstripe   87 Erigeron pringlei (in part)
+ Leaves entire or (in E. anchana) with 1(–2) pairs of deep lobes or teeth; ray laminae without midstripe   (7)
7 (6) Leaves linear (0.5–0.9 mm wide); pappus bristles 16–21   90 Erigeron heliographis
+ Leaves linear-oblanceolate to spatulate; pappus bristles 9–15 or 19–26   (8)
8 (7) Plants 7–22 cm; basal leaves spatulate, (30–)40–90 × 4–8 mm, margins entire or with 1(–2) pairs of lobes or teeth (petioles about 2 times blade lengths); phyllary midnerves orange-resinous, slightly swollen; disc corollas with prominent orange-resinous veins; pappus bristles 19–26   88 Erigeron anchana
+ Plants mostly 3–5 cm; basal leaves linear-oblanceolate to slightly spatulate, 10–30 × 0.5–2(–3) mm, margins entire (petioles, when distinct, about equaling blades); phyllary midnerves greenish yellow, not swollen; disc corollas veins not orange-resinous; pappus bristles 9–13(–15)   89 Erigeron saxatilis
9 (5) Leaves filiform or linear to linear-oblanceolate; cypselae 1.5–2.2 mm   (10)
+ Leaves oblanceolate to spatulate; cypselae 1.8–3.5 mm   (11)
10 (9) Involucres 4–6 × 7–10 mm; rays blue, 4–8 mm   36 Erigeron arenarioides
+ Involucres 3–3.5 × 5–6 mm; rays white, 8–9 mm   37 Erigeron salmonensis
11 (9) Leaves not folding along midveins; ray corollas 7–13 mm; pappus bristleswhite-shiny   79 Erigeron garrettii
+ Leaves commonly folding along midveins; ray corollas 3.5–10 mm; pappus bristles stramineous, dull   (12)
12 (11) Heads 1–4; rays 10–15, laminae reflexing; pappus bristles 12–14;cypselae 1.8–2 mm   85 Erigeron kachinensis
+ Heads 1(–2); rays 13–40, laminae not reflexing; pappus bristles 25–35; cypselae 2–3.5 mm   (13)
13 (12) Leaves basal and reduced cauline; phyllaries glabrous, minutelyglandular; ray corollas 4–6 mm; disc corollas 2.8–4 mm   73 Erigeron watsonii
+ Leaves nearly all basal; phyllaries sparsely to moderately hirsuto-villous, sometimes minutely glandular; ray corollas 6–10 mm; disccorollas 3.6–4.5 mm   74 Erigeron evermannii

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