1. Erigeron annuus (L.) Pers. (daisy fleabane, whitetop fleabane, annual fleabane)
Pl. 233 g, h;
Map 971
Plants annual or
less commonly biennial, with shallow, fibrous roots. Stems 1 to several, (50–)60–150
cm long, usually well branched above the lower 1/3, sparsely to densely
roughened with mostly spreading hairs (the hairs sometimes more appressed
toward the tip). Basal leaves sometimes withered by flowering time, 3–15 cm
long, mostly long-petiolate, the blade broadly oblanceolate to broadly obovate,
short- to long-tapered at the base, mostly rounded at the tip, the margins
coarsely and sharply toothed, the surfaces and margins sparsely to moderately
pubescent with short, relatively stiff, curved hairs. Stem leaves usually
relatively numerous, 1–10 cm long, the lower ones short-petiolate, the median
and upper ones sessile, the blade oblanceolate to elliptic or lanceolate (the
lower leaves rarely obovate), angled or tapered to a mostly sharply pointed
tip, angled, tapered, or narrowly rounded at the base, not or only very
slightly clasping the stem, the margins of all but the uppermost leaves usually
with several sharp teeth on each side, these often produced from below the
midpoint to the tip, the surfaces and margins sparsely to moderately hairy.
Inflorescences rounded to more or less flat-topped panicles, usually open and
often with numerous heads. Involucre 3–5 mm long, the receptacle 6–12 mm in
diameter at flowering, the bracts sparsely to moderately pubescent with more or
less spreading hairs and often also minutely glandular. Ray florets 80–125, the
corolla 4–10 mm long. Disc florets with the corolla 1.5–2.5 mm long. Pappus of
the ray and disc florets of 2 types, an inner series of 10–15 threadlike
bristles 1.2–2.2 mm long and an outer series of several shorter bristles or
slender scales 0.1–0.4 mm long, the ray florets lacking the longer, inner
series. Fruits 0.8–1.0 mm long, sparsely and inconspicuously hairy. 2n=27,
54. May–November.
Common
throughout the state (U.S., Canada; introduced in Europe). Banks of streams and
rivers, margins of ponds and lakes, openings of bottomland and mesic upland
forests, and bottomland and upland prairies; also pastures, old fields, fallow
fields, crop fields, railroads, roadsides, and open, disturbed areas.
Erigeron
annuus is a mostly
triploid taxon that reproduces apomictically. Using allozyme markers, Hancock
and Wilson (1976) showed that multiple genotypes may be present within
populations. Stratton (1991) demonstrated that there was considerable
morphological variation within experimental populations grown under greenhouse
conditions. This genotypic variation and phenotypic plasticity are responsible
in part for difficulties that some botanists have had in distinguishing some
plants of E. annuus from E. strigosus in the field and herbarium.
Frey et al. (2003) studied introduced populations of these species in Europe
and a small number of North American plants, and they concluded that plants
attributed to E. strigosus var. septentrionalis (Fernald & Wiegand)
Fernald should more properly be considered a variety of E. annuus. In
fact, some botanists have suggested that E. strigosus as a whole might
be treated better as a subspecies of E. annuus, but this approach merely
avoids dealing with the problem rather than the more difficult job of
reassessing evolutionary lineages within the group. Further research involving
more in-depth sampling of North American populations of both species will be
necessary to resolve the situation. See the treatment of E. strigosus
for further discussion.
Cronquist
(1947c) called rare plants from Quebec, Canada, with the heads lacking ray
florets var. discoideus (Vict. & J. Rousseau) Cronquist. This rare
mutant should deserve no more recognition than that of a form (if at all).
Steyermark
(1963) noted that plants of E. annuus have been used medicinally as an
astringent, diuretic, and tonic. He also noted that deer frequently browse the
foliage. According to Stratton (1991), a single plant of E. annuus may
produce 10,000–100,000 fruits in one growing season, which helps to account for
the success of the species geographically and ecologically.