Perennials, 5-70 cm, cespitose; short-rhizomatous. Stems 1-5+, ascending to erect (straight, slender, 1-2.5(-3) mm diam.), glabrous. Leaves thin, margins scab­rous to scabrellous or eciliate, apices mucronulate, faces gla­brous; basal persistent or withering by flowering, petiolate (petioles slightly winged, sheathing), blades spatulate to elliptic or oblanceolate, 10-40 × 5-11 mm, bases cuneate to attenuate, margins crenate-serrate, apices obtuse to acute; proximal cauline persistent or withering by flowering, ± broadly winged-petiolate or sessile, blades oblong, lanceolate or elliptic-lanceolate to oblanceolate, or linear-lanceolate, 20-100 × 3-9 mm, bases attenuate to cuneate, slightly clasping, margins serrulate or entire; distal sessile, blades oblanceolate to linear-lanceolate or linear, 10-60 × 1-7 mm, gradually reduced distally, bases cuneate to tapering, margins serrulate or entire, apices acute to acuminate. Heads {(10-)25-100} in paniculiform arrays, branches ascending (1-10 heads per branch). Peduncles ascending, 0.2-2.5+ cm, glabrous, bracts 1-4, subulate to linear. Involucres cylindro-campanulate, 3.3-4.5(-5) mm. Phyllaries in 4-5 series oblong-lancoelate (outer) to linear-lanceolate (inner) or linear (innermost), unequal, bases indurate ¹ / 2 +, margins scarious, erose, hyaline, ciliolate, green zones lanceolate, apices acute to acuminate or caudate, mucronulate or apiculate, sometimes purplish, faces glabous. Ray florets 14-27; corollas white, laminae 4.3-8.2 × 0.7-0.8 mm. Disc florets 20-30; corollas pale yellow becoming purplish, 3-4.1 mm, tubes shorter to nearly equaling funnelform throats, lobes lanceolate, 0.5-1 mm. Cypselae tan (nerves stramineous), obovoid, ± compressed, 3.5-4 mm, 4-5-nerved, faces strigillose; pappi white, 3-3.6 mm. 2n = 16, 32.

Flowering Jul-Aug(-Sept). Damp, rocky and gravelly shores, silt- or loam-filled cracks in rocky rapids of streams or along freshwater estuaries; 0-200+ m; N.B., Nfld. and Labr. (Nfld.), N.S., Que.; Maine, Mass., N.H., N.J., N.Y., R.I., Vt.

Rhizomatous, 1.5-6 dm; stem glabrous below, usually hairy in lines above; lvs glabrous, entire or shallowly toothed, linear or lance-linear to lance-elliptic, the basal petiolate, the others sessile or nearly so, 3-10 cm נ3-10 mm, the upper reduced and mostly rather few; heads relatively few in an elongate, open infl; invol 3.5-5 mm high, glabrous, its narrow bracts well imbricate, with ±elongate green tip; rays 15-30, 3-8 mm, white; lobes of the disk-cors comprising 30-45% of the limb; 2n=16, 32. Seasonally inundated streambanks and shores, often among rocks; s. Que., s. N.S. and c. Me. to N.Y. and the Delaware R. in N.J.; n. Mich.? (A. saxatilis)

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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