|
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.
SELECTED REFERENCES 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.
|
Key to Groups of Erigeron Species
|
|
|
| 1 |
Heads discoid or disciform (pistillate florets 0 or their corollas filiform, lacking laminae) |
|
Group 1 |
| + |
Heads radiate (corollas of pistillate florets bearing laminae, laminae sometimes filiform and hardly surpassing involucres, especially Groups 8 and 11) |
|
(2) |
| |
|
|
|
| 2 (1) |
Plants with herbaceous, leafy runners or slender, scale-leaved rhizomes. |
|
Group 2 |
| + |
Plants without leafy runners or scale-leaved rhizomes |
|
(3) |
| |
|
|
|
| 3 (2) |
Leaves pinnately lobed or dissected |
|
Group 3 |
| + |
Leaves usually entire or dentate, rarely with 1–2 pairs of coarse lobes |
|
(4) |
| |
|
|
|
| 4 (3) |
Annuals, biennials, or short-lived perennials |
|
(5) |
| + |
Perennials |
|
(9) |
| |
|
|
|
| 5 (4) |
Pappus bristles absent on ray and/or disc cypselae |
|
Group 4 |
| + |
Pappus bristles present on ray and disc cypselae |
|
(6) |
| |
|
|
|
| 6 (5) |
Ray laminae nearly filiform, erect |
|
(7) |
| + |
Ray laminae strap-shaped, usually spreading |
|
(8) |
| |
|
|
|
| 7 (6) |
Heads usually in loose, racemiform arrays; pistillate florets in 1 series, all with filiform laminae; pappus bristles not accrescent |
|
114 Erigeron lonchophyllus |
| + |
Heads usually in corymbiform arrays; pistillate florets in 2 zones, outer with nearly filiform laminae, inner tubular and essentially elaminate; pappus bristles accrescent (elongating in fruit to ca. 2 times involucres) |
|
Group 8 (in part) |
| |
|
|
|
| 8 (6) |
Plants fibrous-rooted |
|
Group 5 |
| + |
Plants taprooted |
|
Group 6 |
| |
|
|
|
| 9 (4) |
Leaves 3-lobed or 3-dentate at apices; plants usually with relatively slender, rhizomelike caudex branches (rarely in E. compositus) |
|
Group 7 |
| + |
Leaves not 3-lobed or 3-dentate at apices; plants with or without slender caudex branches |
|
(10) |
| |
|
|
|
| 10 (9) |
Pistillate florets in 2 zones, outer with nearly filiform, erect laminae, sometimes shorter than involucres, inner tubular and essentially elaminate; pappus bristles accrescent (elongating in fruit to ca. 2 times involucres) |
|
Group 8 (in part) |
| + |
Pistillate florets all with strap-shaped, spreading laminae, occasionally reduced, nearly filiform and erect (in some arctic, monocephalous species); pappus bristles not accrescent (except in E. uniflorus var. eriocephalus). |
|
(11) |
| |
|
|
|
| 11 (10) |
Rays yellow |
|
Group 9 |
| + |
Rays white or blue to pink |
|
(12) |
| |
|
|
|
| 12 (11) |
Plants fibrous-rooted (usually rhizomatous, rhizomes sometimes abbreviated or apparently lacking in E. glabellus) or without an evident taproot (taproot weakly developed or not collected because of extensive rhizome or caudex system) |
|
(13) |
| + |
Plants usually evidently taprooted (sometimes also with branched caudices) |
|
(16) |
| |
|
|
|
| 13 (12) |
Rhizomes or caudex branches slender (without apparent well-defined central axes); ray laminae strap-shaped |
|
Group 10 |
| + |
Rhizomes thickened (usually evident as single central axes; abbreviated or apparently lacking in E. glabellus); ray laminae filiform or strap-shaped |
|
(14) |
| |
|
|
|
| 14 (13) |
Basal and proximal cauline leaves reduced or present only as scales (cauline largest at midstem); ray laminae not coiling; cypselae 5–6-nerved, glabrous |
|
2 Erigeron hyssopifolius (in part) |
| + |
Basal and proximal cauline leaves usually well developed (sometimes withering by flowering); ray laminae usually coiling, often tardily or only at tips (filiform and straight in some species of Group 11); cypselae mostly 2(–4)-nerved (4–7-nerved in E. glacialis and E. howellii), usually strigose |
|
(15) |
| |
|
|
|
| 15 (14) |
Plants 2–25(–35) cm; leaves mostly basal (bases of cauline not clasping orsubclasping); heads 1–3 |
|
Group 11 |
| + |
Plants (5–)15–90 cm; leaves basal and cauline or mostly cauline (bases ofcauline usually clasping to subclasping); heads 1–21 |
|
Group 12 |
| |
|
|
|
| 16 (12) |
Perennials (short-lived), caudices usually not branched (stems and leaves arisingfrom near roots) |
|
Group 13 |
| + |
Perennials, caudices usually branched |
|
(17) |
| |
|
|
|
| 17 (16) |
Leaves all or mostly cauline (basal not markedly larger than cauline, internodes relatively short), blades linear or filiform to narrowly oblong, essentially uniform; California and immediately adjacent areas |
|
Group 14 |
| + |
Leaves mostly basal or basal and cauline (if basal withering by flowering, then persistent leaf bases usually evident), oblanceolate, obovate, or spatulate (if linear or filiform then basal larger than cauline and internodes relatively wide); w North America |
|
(18) |
| |
|
|
|
| 18 (17) |
Proximal leaves loosely clustered (not in persistent rosettes, usually with evident internodes), blades oblanceolate or linear to filiform; stems and leaves ± strigose |
|
(19) |
| + |
Proximal leaves tightly clustered (usually in persistent rosettes, internodes not readily evident), blades 1- or 3-nerved, linear to oblanceolate, obovate, or spatulate; stems and leaves strigose to hirsute, villous, or lanate-villous |
|
(20) |
| |
|
|
|
| 19 (18) |
Plants 20–70 cm; leaves oblanceolate; pappi readily falling, of (8–)10–12 bristles; stems not more densely hairy proximally than distally |
|
3 Erigeron neomexicanus (in part) |
| + |
Plants 10–30(–50) cm; leaves linear to filiform; pappi persistent, of 20–30 bristles; stems more densely white-strigose proximally than distally (hairs loosely appressed to ascending, fine) |
|
53 Erigeron filifolius (in part) |
| |
|
|
|
| 20 (18) |
Basal leaves obovate-spatulate, 5–25 mm wide, cauline little reduced distally or relatively even-sized, bases usually subclasping (except in E. oreganus); heads usually 1, sometimes 2–5 from proximal axils |
|
Group 17 |
| + |
Basal leaves linear to oblanceolate or spatulate, (0.5–)1–13(–15) mm wide, cauline usually gradually or abruptly reduced distally, bases not clasping or subclasping; heads 1–16 |
|
(21) |
| |
|
|
|
| 21 (20) |
Petioles prominently ciliate (hairs spreading, thick-based); leaves mostly linear to narrowly oblanceolate |
|
(22) |
| + |
Petioles not prominently ciliate (or if so, hairs thin-based or ascending to loosely appressed); leaves linear to obovate or spatulate |
|
(23) |
| |
|
|
|
| 22 (21) |
Leaves basal and cauline or sometimes mostly basal; heads 1–5; ray laminae reflexing (coiling in E. davisii, added to key for contrast with E. engelmannii) |
|
Group 15 |
| + |
Leaves mostly basal; heads 1; ray laminae sometimes coiling, not reflexing |
|
Group 16 |
| |
|
|
|
| 23 (21) |
Stems and leaves glabrous or glabrate (minutely glandular in E. nauseosus, sometimes minutely glandular distally in E. arenarioides); phyllaries minutely glandular, rarely also sparsely strigose or hirsuto-villous (sometimes glabrous, eglandular), often purplish; ray laminae reflexing, coiling, or straight and spreading |
|
Group 18 |
| + |
Stems and/or leaves strigose or sericeous to hirsute or villous; phyllaries strigose to hirsute, sometimes glandular, rarely purplish; ray laminae coiling or straight and spreading (reflexing in E. parishii and E. canus) |
|
(24) |
| |
|
|
|
| 24 (23) |
Stems with spreading hairs |
|
Group 19 |
| + |
Stems with appressed hairs |
|
(25) |
| |
|
|
|
| 25 (24) |
Stems ascending to decumbent, sometimes purplish proximally; basal leaves (1–)3-nerved, usually linear to oblanceolate, sometimes obovate; stems and leavesstrigose to hirsute |
|
Group 20 |
| + |
Stems mostly erect, usually not purplish proximally; basal leaves linear to oblanceolate or spatulate; stems and leaves usually strigose or sericeous (hairs usually whitish, closely appressed, even-length) |
|
(26) |
| |
|
|
|
| 26 (25) |
Leaves mostly spatulate |
|
Group 21 |
| + |
Leaves linear to oblanceolate |
|
(27) |
| |
|
|
|
| 27 (26) |
Leaf bases of basal and proximal cauline leaves abruptly widened, thickened, and white-indurate |
|
Group 22 |
| + |
Leaf bases sometimes widened, not thickened and white-indurate |
|
Group 23 |
|
|
List of Keys
|
List of lower taxa
| Related Links (opens in a new window) |
|
Treatments in Other Floras @ www.efloras.org
Other Databases
|
|
|
|
|
|
|
