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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 12

1 Phyllaries villoso-lanate or hirsuto-villous (at least basal part of hairs with black or reddish to purple cross walls), minutely glandular   (2)
+ Phyllaries glandular and/or variously hairy (hair cross walls not distinctly colored)   (3)
2 (1) Phyllaries hirsuto-villous (hair cross walls black)   141 Erigeron coulteri
+ Phyllaries densely villoso-lanate (hair cross walls reddish to purple)   143 Erigeron elatior
3 (1) Stems procumbent to decumbent-ascending (plants forming dense colonies); leaves fleshy   139 Erigeron glaucus
+ Stems erect to ascending (not forming dense colonies); leaves not fleshy   (4)
4 (3) Primary rhizomes slender, producing scale-leaved runners or stoloniform rhizomes   (5)
+ Primary rhizomes relatively thick, sometimes woody, fibrous-rooted   (8)
5 (4) Stems usually abruptly dilated immediately proximal to heads; e United States   130 Erigeron pulchellus (in part)
+ Stems not abruptly dilated; w United States   (6)
6 (5) Plants 5–15 cm; stems sparsely pilose (hairs spreading-ascending), strigose proximally, eglandular; involucres 4–5 × 8–10 mm; ray florets 32–45, corollas 8–11 mm; pappus bristles 15–19   146 Erigeron kuschei (in part)
+ Plants 15–60 cm; stems hirsute to hirtellous, glandular to nearly eglandular; involucres 6–9 × 9–19 mm; ray florets 40–99, corollas 11–20 mm; pappus bristles 20–32   (7)
7 (6) Stems usually glabrous, sometimes sparsely hirsuto-pilose proximal to heads, minutely glandular to nearly eglandular; basal leaves usually persistent, spatulate; phyllaries usually glabrous, sometimes sparselyvillous at bases, minutely glandular   144 Erigeron eximius (in part)
+ Stems hirsute to hirtellous (hairs retrorsely spreading), eglandular or sparsely glandular; basal leaves usually withering by flowering, elliptic-ovate to spatulate-obovate; phyllaries piloso-hirsute, sometimes minutely glandular   142 Erigeron rybius (in part)
8 (4) Phyllaries relatively densely hairy, eglandular or glands essentially obscured by hairs   (9)
+ Phyllaries sometimes sparsely to moderately hirsute to villous (hairs not obscuring glands), glandular   (13)
9 (8) Plants cespitose (stems from fibrous-rooted rhizomes or caudices with woody, rhizomelike branches); involucres 5–6 × 8–13 mm; phyllaries usually purplish   151 Erigeron hessii
+ Plants not cespitose (caudices simple or branched); involucres 5–9 × 9–22 mm; phyllaries greenish   (10)
10 (9) Plants with relatively short and thickened caudices or rhizomes, usually appearing fibrous-rooted; phyllaries hirsute to strigose, eglandular   38 Erigeron glabellus (in part)
+ Plants evidently rhizomatous; phyllaries hirsute to villous, glandular or eglandular   (11)
11 (10) Phyllaries villoso-hirsute, eglandular; alpine habitats, w Canada,Alaska, Oregon, Washington   131 Erigeron peregrinus (in part)
+ Phyllaries hirsute to piloso-hirsute, densely minutely glandular; lower elevation habitats, Rocky Mountains, Alberta, United States   (12)
12 (11) Stems strigose to strigoso-hirsute or hirsute, eglandular; basal leaves often 3-nerved, margins shallowly serrate, faces loosely strigose; rays 25–80, white; disc corollas 2.9–4 mm   140 Erigeron arizonicus (in part)
+ Stems densely hirsute to hirsutulous or glabrous, minutely glandular to stipitate-glandular; basal leaves margins entire, faces glabrous or sparsely hirsute; rays 75–150, mostly blue to purple; disc corollas 3.5–4.5 mm   145 Erigeron formosissimus (in part)
13 (8) Leaves often prominently 3-nerved, margins coarsely dentate to shallowly serrate or entire   (14)
+ Leaves margins usually entire, sometimes (E. howellii) denticulate or shallowly serrate   (15)
14 (13) Leaf margins entire or shallowly serrate, faces loosely strigose; phyllaries moderately piloso-hirsute; ray corollas 8–10 mm; Arizona, New Mexico   140 Erigeron arizonicus (in part)
+ Leaf margins usually coarsely dentate (teeth 1–5 pairs), sometimes entire, faces strigose to hirsute; phyllaries glabrous or moderately villous to white-hirsuto-villous (sometimes only at peduncle-involucre region); ray corollas 10–15 mm; California, Oregon, Washington   147 Erigeron aliceae
15 (13) Stems 1-nerved, strigillose (hairs crinkly) or glabrous distally, eglandular or nearly so; phyllaries glabrous or sparsely hairy, densely glandular   (16)
+ Stems hirsute distally or throughout, glandular or eglandular; phyllaries sometimes hirsute to villous, glandular   (19)
16 (15) Stems strigillose (hairs crinkly) at least distally; ray laminae 1.5–3 mm wide   (17)
+ Stems glabrous distally; ray laminae ca. 1 mm or 1.5–3 mm wide   (18)
17 (16) Stems strigillose, more densely so distally; basal and proximal cauline leaves linear-oblanceolate to broadly lanceolate or spatulate; ray corollas usually blue to rose purple or pink, sometimes white, 8–16(–25) mm; at 1300–3800 m   132 Erigeron glacialis (in part)
+ Stems proximally glabrous, distally strigillose; basal and proximal cauline leaves spatulate; ray corollas white, 13–25 mm; at (60–)500–1200(–1500) m   133 Erigeron howellii
18 (16) Plants 30–80(–100) cm; rays 75–150, corollas 8–16 × ca. 1 mm   134 Erigeron speciosus (in part)
+ Plants (10–)15–30 cm; rays 20–45, corollas 7–10 × ca. 1.5–3 mm   148 Erigeron cervinus
19 (15) Ray laminae 1.5–3 mm wide; cypselae 2.5–2.8 mm, (4–)5(–7)-nerved   (20)
+ Ray laminae ca. 1 mm wide; cypselae (1.3–)1.5–2 mm, 2(–4)-nerved   (21)
20 (19) Phyllary margins usually ciliate, faces sparsely to moderately villoso-hirsute, usually sparsely gland-dotted apically, rarely throughout   131 Erigeron peregrinus (in part)
+ Phyllaries usually glabrous (rarely outer faces and margins sparsely villous), densely and evenly stipitate-glandular   132 Erigeron glacialis (in part)
21 (19) Stems ascending; cauline leaves gradually reduced distally   145 Erigeron formosissimus (in part)
+ Stems usually erect; cauline leaves usually nearly even-sized, sometimes mid largest   (22)
22 (21) Cauline leaves ending 1.5–9 cm proximal to heads (peduncles distinct);rays white   140 Erigeron arizonicus (in part)
+ Cauline leaves continuing to immediately proximal to heads (peduncles very short); rays mostly blue to purplish.   (23)
23 (22) Stems and leaves prominently and densely stipitate-glandular (glands 0.2–0.5 mm), stems sometimes sparsely pilose (hairs 1–2 mm); pappi: outer of scales, inner of 14–22 bristles   137 Erigeron vreelandii
+ Stems and distal leaves eglandular to minutely glandular or inconspicuously stipitate-glandular (if stipitate, glands 0.1–0.4 mm), stems, leaves, and phyllaries glabrous or hirsute to hirsuto-pilose (hairs 0.5–2 mm); pappi: outer of setae, inner of 20–30 bristles   (24)
24 (23) Stems moderately to densely hirsute, eglandular; leaves evenly hirsute to strigoso-hirsute, usually eglandular   135 Erigeron subtrinervis
+ Stems glabrous or hirsuto-pilose, sometimes minutely glandular; leaves glabrous or sparsely hirsuto-pilose, eglandular or minutely glandular   (25)
25 (24) Stems sparsely hirsuto-pilose (hairs 1–2 mm), sometimes minutely glandular   136 Erigeron uintahensis
+ Stems glabrous or sparsely hirsuto-pilose (hairs 0.5–1 mm), often minutely glandular distally   134 Erigeron speciosus (in part)

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