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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 19

1 Leaves spatulate, bases of blades abruptly contracted to petioles   (2)
+ Leaf blades linear to lanceolate, oblanceolate, or oblanceolate-spatulate, bases usually attenuate to petioles   (5)
2 (1) Stems villous to hirsuto-villous   (3)
+ Stems hirsute to hirtellous   (4)
3 (2) Phyllaries eglandular or sparsely glandular near apices and along midregion; stems and leaves eglandular; leaf faces strigose to hirsuto-villous, less densely so abaxially;cypselae 1.3–1.8 mm   76 Erigeron uncialis (in part)
+ Phyllaries evenly and densely glandular; stems and leaves glandular; leaf faces equallyhirsuto-canescent; cypselae 1–1.2 mm   77 Erigeron cavernensis
4 (2) Stems moderately to densely hirtellous (hairs deflexed), eglandular; leaves folding along midnerves; rays deep blue or violet to rose-purple; disc corollas 4.2–6.3 mm   78 Erigeron asperugineus
+ Stems densely hirsute (hairs spreading), minutely glandular; leaves not folding alongmidnerves; rays white to pink; disc corollas 2.5–3 mm   82 Erigeron maguirei (in part)
5 (1) Leaf faces glabrous or glabrate abaxially, hairy adaxially (both faces hairy in E. parryi)   (6)
+ Leaf faces hairy   (10)
6 (5) Phyllaries densely glandular, villous hairs with blackish purple crosswalls; rays purple to lavender; leaf apices acute; pappus bristles 15–24   43 Erigeron lackschewitzii
+ Phyllaries sparsely and inconspicuously glandular, non-glandular hairs with or without colored crosswalls; rays white to pink or bluish; leaf apices obtuse to rounded or (in E. ochroleucus) acute; pappus bristles (6–)7–15 or 15–25   (7)
7 (6) Stems hirsute; leaves 10–25 mm, faces hirsute to hirsuto-strigose   40 Erigeron parryi
+ Stems hirsutulous to villous, lanate-villous, or villosulous; leaves 10–90(–120) mm, abaxial faces essentially glabrous, adaxial strigose or sparsely villous.   (8)
8 (7) Stems finely hirsutulous to villosulous; leaf apices obtuse to rounded; rays 15–35, bluish to purplish, rarely white; pappus bristles 15–20   39 Erigeron rydbergii
+ Stems loosely strigose to puberulo-strigose or villous; leaf apices acute or obtuse to rounded; rays (12–)20–62(–85), white to pinkish, bluish, or lavender; pappus bristles (6–)7–15   (9)
9 (8) Stems (1–)2–6(–12) cm, strigose to short-villous, usually arising from short, thickened caudex branches; leaves (5–)10–50(–60) mm, apices obtuse to rounded, adaxial faces sparsely loosely strigose, abaxial glabrate or glabrous, shiny; involucres (3–)4–6(–8) mm; phyllary hairs usually with colored crosswalls; rays (12–)20–44(–85); pappus bristles (6–)7–11   41 Erigeron radicatus
+ Stems (2–)8–18(–30) cm, usually loosely strigose, arising from a nearly common point near apices of thick taproots, caudices usually simple; leaves (20–)40–90(–120) mm, apices acute, faces usually strigose at least on proximal 1 / 3 – 3 / 4 of blade, adaxial glabrous distally; involucres 5.5–7 mm; phyllary hairs usually without colored crosswalls; rays 30–62; pappus bristles 12–15   42 Erigeron ochroleucus
10 (5) Leaf apices acute; basal leaves (30–)50–160 mm; stems usually purplish proximally; heads 1–10(–18)   (11)
+ Leaf apices usually rounded to obtuse; basal leaves mostly (15–)20–90 mm; stems greenish proximally (except E. jonesii); heads 1–5   (13)
11 (10) Cauline leaves usually smaller than basal; heads 1–4(–7)   10 Erigeron eatonii
+ Cauline leaves gradually or little reduced from basal, usually continuing relatively even-sized nearly to heads; heads 1–10(–18)   (12)
12 (11) Phyllaries flat, densely hirsute to hirsuto-villous, sometimes sparsely minutely glandular; rays 35–65, corollas 7–13 mm, laminae coiling at apices; disc corollas 4–5.3 mm; pappus bristles 20–30   6 Erigeron corymbosus
+ Phyllaries commonly strongly keeled to nearly folded, moderately hirsuto-villous or villous, densely minutely glandular; rays 12–36, corollas 4.5–8 mm, laminae slightly coiling or not; disc corollas 2.5–3.5 mm; pappus bristles 12–24   12 Erigeron lassenianus
13 (10) Leaves 3-nerved   (14)
+ Leaves 1-nerved   (15)
14 (13) Stems greenish proximally; phyllaries densely hirsuto-canescent to hirtellous; raylaminae coiling   14 Erigeron caespitosus (in part)
+ Stems purplish proximally; phyllaries sparsely to moderately hirsute; ray laminae not coiling or reflexing   13 Erigeron jonesii
15 (13) Stems hirsute (hairs spreading, not deflexed), densely minutely glandular   82 Erigeron maguirei (in part)
+ Stems hirsute or hirsutulous to hirtellous (hairs deflexed or not), eglandular or glandular only distally   (16)
16 (15) Stem hairs spreading to ascending; leaves 10–25(–50) × 0.8–2 mm   40 Erigeron parryi
+ Stem hairs deflexed; leaves 15–70 × 2–6(–8)   (17)
17 (16) Phyllaries hirsute to hirsuto-villous, eglandular; involucres 5–7 mm; raycorollas 6–10 mm, blue; pappus bristles 20–25   16 Erigeron goodrichii (in part)
+ Phyllaries strigose to strigulose or finely hirsuto-villous, minutely glandular; involucres 3.7–5.2 mm; ray corollas 5–6 mm, blue to pink or white;pappus bristles 12–20   15 Erigeron abajoensis (in part)

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