19. Eurybia (Cass.) S.F. Gray
Plants perennial
herbs, usually with elongate, fleshy rhizomes, often forming colonies, the
rootstock sometimes somewhat woody in E. hemispherica. Stems usually
solitary, erect or ascending, unbranched below the inflorescence, with fine,
longitudinal lines, glabrous or hairy. Basal leaves present or absent at
flowering. Stem leaves gradually reduced toward the tip, variously shaped,
glabrous or hairy. Inflorescences either slender racemes or flat-topped to
somewhat dome-shaped panicles or loose clusters, rarely of solitary heads, the
heads nearly sessile to long-stalked, the bracts relatively few and more or
less leaflike. Heads radiate, not sticky or resinous. Involucre 7–12 mm long,
broadly cup-shaped to obconical or slightly bell-shaped. Involucral bracts
either in 5–7 unequal or in 2–4 nearly equal, overlapping series, variously
shaped, the tip ascending or more or less spreading, with a pale, thickened
base, this with or without a slender, green midvein, with an ovate to broadly
diamond-shaped green portion toward the tip, this sometimes with narrow purple
margins. Receptacle flat or shallowly convex, with minute, irregular ridges
around the concave attachment points of the florets. Ray florets 9–35,
pistillate, the corolla white or lavender to purple. Disc florets 15–80,
perfect, the corolla 5.5–8.0 mm long, relatively shallowly lobed, yellow,
turning reddish purple to brownish purple after the pollen has been shed, not
persistent at fruiting. Pappus of the ray and disc florets similar (the
outermost bristles sometimes appearing slightly shorter), apparently of 1 (but
often actually 2) series of numerous (60–80) finely barbed bristles 5–8 mm
long, the innermost bristles sometimes slightly broadened toward the tip, light
tan to pale orangish brown. Style branches with the sterile tip (beyond the
stigmatic lines) (0.2–)0.3–0.5 mm long, linear to lanceolate. Fruits narrowly
obconical to oblong-ellipsoid, oblong-obovoid, or nearly cylindrical, sometimes
slightly flattened, with 7–16 yellowish brown ribs, glabrous or hairy, brown to
greenish brown, rarely tan. About 28 species, U.S., Canada, Europe, Asia.
Eurybia is part of an as-yet poorly understood
group of genera that includes the large Aster-segregate Symphyotrichum
as well as several genera of western North American plants formerly treated in Aster
and/or Haplopappus and currently known as the Machaeranthera Nees
alliance (Semple et al., 2002). The generic limits of Eurybia require
further study, and it is possible that some of the species presently included
in the genus are more closely related to those in other genera (Semple et al.,
2002). In Missouri, the three species are all morphologically relatively
distinct.