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Published In: Species Plantarum 2: 863. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView 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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18. Erigeron L. (fleabane)

Plants annual or perennial herbs, lacking taproots, sometimes with rhizomes or stolons, variously hairy. Stems 1 or few to several, erect or ascending, unbranched or more commonly branched, finely to coarsely angled or longitudinally lined. Basal leaves absent or more commonly present at flowering. Stem leaves progressively reduced toward the tip, sessile or short-petiolate, the blade linear to lanceolate, oblanceolate, or oblong-lanceolate, the base sometimes somewhat clasping the stem, the margins entire or relatively few-toothed above the midpoint. Inflorescences panicles or sometimes (in E. pulchellus) a small cluster or solitary head at the stem or branch tips, the heads long-stalked to nearly sessile, the inflorescence branches with few to several small, leaflike bracts. Heads radiate (rarely discoid in E. strigosus), not sticky or resinous. Involucre cup-shaped to broadly cup-shaped or slightly bell-shaped. Involucral bracts in 2 or 3(4) equal or subequal, overlapping series, narrowly oblanceolate to narrowly lanceolate or linear, the tip ascending (sometimes loosely so in E. pulchellus), with a relatively broad (slender elsewhere), uniform, green central stripe (often with a slender, yellow or orange midvein) and with relatively narrow, thin, pale margins, sometimes purplish-tinged toward the tip. Receptacle flat or shallowly convex, relatively smooth (the veins leading to the florets often appearing as raised points after the fruits have been shed). Ray florets usually numerous (50–400) in 1–4 series, pistillate, the corolla usually conspicuous (occasionally a few of the innermost ray florets with reduced or absent corollas), relatively slender, white or often tinged with pink, lavender, or blue, especially with age or on the undersurface, shed before fruiting. Disc florets numerous (more than 100), perfect, yellow, shed before fruiting. Pappus of the ray and disc florets similar or of 2 types, of relatively few to numerous (8–30) capillary bristles and usually also an outer series of fewer short bristles or narrow scales, usually white, the pappus of the ray florets sometimes with only the outer, shorter series present. Style branches with the sterile tip (beyond the stigmatic lines) 0.1–0.3 mm long, lanceolate to broadly triangular. Fruits narrowly oblong-obovate (slightly tapered toward the base) in outline, flattened, the angles usually with thickened nerves or ribs, rarely with an additional nerve on each face, the surface sparsely hairy or glabrous, pale tan to light yellowish brown. About 390 species, nearly worldwide, most diverse in temperate montane regions.

Thus far, most botanists have resisted the temptation to subdivide Erigeron into smaller genera. In fact, the segregates Conyza and Aphanostephus, which Cronquist (1943, 1947c) and Shinners (1946b) retained as genera separate from Erigeron, should perhaps be reintegrated into the genus, based on molecular data (Noyes, 2000a). In temperate North America, where more than 170 species occur, the greatest diversity is in the western mountains, where numerous narrowly endemic taxa grow. The molecular studies of Noyes (2000a), which involved samples from nearly 70 species spread across the taxonomic and geographic diversity of Erigeron, provided support for the natural (monophyletic) circumscription of the genus and suggested a North American origin for it.

That said, the morphological characters separating Erigeron from some other genera of the tribe Astereae are rendered less effective by variation within some species in each of the groups. In the eastern half of the United States, the general rule of thumb has been that a plant flowering before July with relatively numerous ray florets and subequal involucral bracts having uniform, green central stripes is likely an Erigeron, whereas a plant flowering after July with somewhat fewer ray florets and unequal involucral bracts in which the green stripe is expanded toward the tip is probably an aster (Doellingeria, Eurybia, Symphyotrichum). However, in individual species one or more of these characters are difficult to interpret or break down, and the two groups have overlapping flowering periods from about August to October. In the western United States, the differences between the two groups are further blurred by the presence of other related genera, such as Machaeranthera Nees and its segregates. In Missouri, care also must be taken to avoid confusion between Erigeron and Boltonia, which differ primarily in their pappus types and in the generally later flowering period in the latter.

 

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1.1. Plants with long rhizomes or stolons, often occurring in large colonies; receptacle 1220 mm in diameter at flowering; disc florets with the corolla 4.56.0 mm long ... 3. E. PULCHELLUS

Erigeron pulchellus var. pulchellus
2.1. Plants sometimes with few short offsets (in E. philadelphicus) but not producing rhizomes or stolons, not colonial; receptacle 615 mm in diameter at flowering; disc florets with the corolla 1.53.5 mm long

3.2. Stem leaves with the base rounded to shallowly cordate and more or less clasping the stem; ray florets 120400; disc corollas 2.53.5 mm long ... 2. E. PHILADELPHICUS

Erigeron philadelphicus
4.2. Stem leaves with the base tapered to narrowly rounded, not or only slightly clasping the stem; ray florets 50125; disc corollas 1.52.5 mm long

5.3. Pappus of the ray and disc florets similar, both with 1 or more inner series of longer bristles and an outer series of shorter bristles or scales; stems 1045 cm long; leaves 15 cm long ... 5. E. TENUIS

Erigeron tenuis
6.3. Pappus of the ray and disc florets dissimilar, the disc florets with 1 or more inner series of longer bristles and an outer series of shorter bristles or scales, the ray florets lacking the inner series of longer bristles; stems 30150 cm long; leaves 115 cm long (species sometimes difficult to distinguish)

7.4. Stems (50)60150 cm long, the hairs mostly spreading; stem leaves usually relatively numerous, the blade oblanceolate to elliptic or lanceolate, all but the uppermost usually with several sharp teeth on each side, these often produced from below the midpoint to the tip ... 1. E. ANNUUS

Erigeron annuus
8.4. Stems 3070(90) cm long, the pubescence mostly of appressed to ascending hairs (some of the longer hairs sometimes spreading toward the tip); stem leaves often relatively few, the blade linear to oblanceolate, the margins entire or with few irregular teeth toward the tip ... 4. E. STRIGOSUS
Erigeron strigosus var. strigosus
 
 
 
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