Annuals or perennials, 5-120 cm; taprooted or with caudices (in perennial species; M. borealis rhizomatous). Stems 1-30+, erect. simple or relatively few- to many-branched (naked or leafy proximally and often distally), glabrous or scurfy-pubescent (especially proximal to heads). Leaves mostly basal, cauline 0 or reduced; petiolate (petioles broad to narrow); blades linear to lanceolate or oblanceolate, margins entire, lacerate, dentate, or pinnately lobed (often with narrow rachises and linear lobes; apices acuminate or acute to obtuse, faces glabrous or lightly scurfy-puberulent). Heads borne singly (nodding or inclined in bud, erect in flower and fruit). Peduncles (erect or curved-ascending) not distally inflated, ebracteate (annuals) or leafy (perennials except M. borealis). Calyculi 0 (outer phyllaries forming calyculiform series in annuals). Involucres fusiform, ovoid, globose, or campanulate, 3-30 mm diam. Phyllaries 5-40 in 3-5 series, unequal (outer usually shorter, ± deltate, inner ± lanceolate), herbaceous (midveins often thickened; abaxial faces glabrous or scurfy-puberulent, sometimes black-villous, often adaxially black-villous and minutely white-strigillose). Receptacles flat to low-convex, pitted, glabrous, epaleate. Florets 5-300; corollas yellow to orange or white, outer often purplish abaxially. Cypselae gray to brown or purplish, sometimes purplish-spotted, columnar, obconic, or fusiform (basal callosities knoblike), apices truncate, ribs 10-15, smooth or scabrous (white-villous on marginal cypselae in some species); pappi persistent, usually of 5-30, silvery to yellowish, brownish, or blackish aristate scales (often reduced to 0-4 in M. douglasii, of 24-48 bristles in M. borealis), scale bodies deltate, lanceolate, oblong, ovate, orbiculate, or linear, apices obtuse to acute or lacerate, faces glabrous or villous, aristae barbellulate to barbellate or plumose. x = 9.

A broad circumscription of Microseris, including Apargidium and excluding Nothocalaïs, has usually been accepted (e.g., K. L. Chambers 1955, 1960). Recently, molecular data have led to reinstatement of the monotypic genus Uropappus and separation of two other species as the allotetraploid genus Stebbinsoseris (R. K. Jansen et al. 1991b; Chambers 1993c). A large body of literature has resulted from use of Microseris as a model genetic system by K. Bachmann and colleagues (e.g., Bachmann et al. 1979; Bachmann 1992; Bachmann and J. Battjes 1994). Differences in the diploid DNA amount within and between species have been studied by H. J. Price and colleagues (Price and Bachmann 1975; Price et al. 1981, 1983). Additional genetic studies, not referenced here, have involved three species from Australia, New Zealand, and Chile, widely disjunct from the main center of distribution in western North America. Ten of the species are diploid (2n = 18); the four tetraploid species (2n = 36) are of alloploid origin. The nine North American perennial taxa are closely related and mostly allopatric, occupying different habitats or climatic zones. The five annual species, which sometimes occur in sympatric clusters, are difficult to distinguish without the presence of cypselae.

In keys and descriptions, measurements of pappus scales exclude aristae.

Fls all ligulate and perfect, yellow; invol campanulate or narrower; achenes columnar to fusiform, but scarcely beaked, with a whitish basal callosity, ca 10-ribbed; pappus of 5-many members, these commonly with paleaceous base and slender, bristle-like tip, varying (in spp. approaching Agoseris) to merely obscurely flattened capillary bristles; lactiferous herbs with a taproot, entire to pinnatifid lvs, and 1-many heads on long naked peduncles. 25, chiefly w. U.S.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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