Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.

Primary thallus: squamulose, persistent; squamules: 1-6 mm long, 2-5 mm wide, sometimes with granular soredia podetia: 2-30 mm tall, 1-4 mm wide, grayish to whitish green, unbranched to sparingly branched, subulate or blunt, not cup-forming surface: sorediate, with disappearing cortex on upper portions, but basally thickly corticate (also below apothecia); soredia: coarse at base, sometimes intergrading with isidioid structures Apothecia: scarce, 0.5-3 mm wide, red ascospores: oblong, 8-13 x 3-4 micro meter Pycnidia: common, on primary squamules or tips of podetia, ovoid to cylindrical, with red gelatin conidia: 3-8 x 0.5-1 micro meter Spot tests: K+ bright yellow, persistent, or K-, C+ & KC+ canary yellow, or C- & KC-, P+ orange, or P-, UV- Secondary metabolites: thallus with two major chemotypes: (1) thamnolic, barbatic (inconstant), and didymic (accessory) acids; (2) barbatic acid, didymic acid (accessory); many minor accessory metabolites also present (Ahti 2000); apothecial discs with rhodocladonic acid as a red pigment. Habitat and ecology: on dead wood, tree bases, or sometimes over soil or rocks World distribution: all continents (Antarctica uncertain); mainly temperate to boreal Sonoran distribution: Arizona, southern California, Baja CalIfornia, and Sinaloa. Notes: Cladonia macilenta is often divided into two species, called C. macilenta and C. bacillaris (the nomenclature is in need of clarification) based on the presence or absence of thamnolic acid (revealed by K and P reactions). They are here regarded as chemotypes, following Christensen (1987) and Ahti (2000), although some authors claim that they have subtle morphological differences. The barbatic acid chemotype seems to be the only one in inland areas of the Sonoran region, while the thamnolic chemotype is more frequent in the coastal lowlands.

Primary squamules persistent, small to middle-sized, up to 3 mm long, crenate to lobed; upper side glaucescent to olive-glaucescent; underside white to darker at the base; esorediate or more commonly sorediate at the margin and on the underside. Podetia growing from the upper side of the primary squamules; varying in height up to 50 mm but usually smaller, up to 10-20 mm; commonly broadening slightly to the blunt tip, producing a club-shaped podetium, rarely sharp-pointed, usually covered with greenish farinose soredia, the base with only a very short corticate patch, white throughout after dispersal of soredia although in one form with yellowish spots which turn violet with K. Apothecia scarlet, small to medium-sized, up 2 mm; often imbedded in the tips of the podetia. Pycnidia on the surface and margins of the primary squamules.

Reactions: K-, KC- or KC+ yellowish. P-.

Contents: barbatic acid with accessory' usnic and didymic acids and F.

This species grows on old logs, tree bases, earthen banks, and humus. It is cosmopolitan, in North America being low arctic boreal and temperate, ranging over most of the United States.