Shrubs, usually densely branched, forming mats or clumps [erect or decumbent]. Roots tuberlike and/or diffuse, also often adventitious. Stem segments firmly attached in most species in the flora to easily dislodged, cylindric-clavate, usually curving upward from near bases, sometimes subspheric, subequal in length, glabrous, strongly tuberculate, sometimes appearing ribbed; areoles ± circular, 1-6 mm diam.; wool white, gray, or yellow. Spines with epidermis sheath deciduous at apices only, exposing yellow spine tips; at least 1 of major spines in distal areoles angular-flattened to ribbonlike, sometimes cross-striate, sometimes bulbous based. Glochids commonly increasing greatly in number with time, in distal areoles, white, yellow, or brown. Flowers bisexual, radially symmetric; inner tepals bright yellow or rose to purple. Pollen spinulo-punctate, not reticulate (cylindropuntioid type). Fruits yellow to brownish, narrowly obconic to ellipsoid when fertile, fleshy at first, soon drying, smooth, sometimes spiny; areoles bearing conspicuous tuft of long, white to tan wool. Seeds yellowish white or pale yellow to brownish, suborbicular (to rectangular) or flattened, 3-6 mm, smooth or with rows of raised bumps; funicular girdle encircling seeds, not protruding. x = 11.

PLANT: Shrubs trailing or clump-forming.

STEM: segments firmly attached (most of our spp.) to easily dislodged, subequal in length, cylindric and usually clavate, curving upward from near bases, to subspheric, glabrous.

SPINES: with epidermis sheath deciduous at apices, exposing yellow spine tips; at least one of the major spines angular-flattened to ribbon-like.

GLOCHIDS: commonly increasing greatly in numbers as areoles age. FLOWERS: ovary and floral tube bearing large tufts of white to tan wool.

FRUIT: narrowly obconic to ellipsoid, smooth, fleshy at first but soon drying, sometimes spiny.

SEEDS: pale yellow to brownish; discoid, the girdle smooth.

NOTES: Spp. 13; N. Amer. deserts.

REFERENCES: Pinkava, Donald J. 1999. Cactaceae. Ariz. - Nev. Acad. Sci. 32(1).