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.

Distribution

s United States, n Mexico.

Discussion

Species 14 (8 in the flora).

Selected References

Pinkava, D. J. 1999b. Cactaceae cactus family: Part 4. Grusonia.... J. Arizona-Nevada Acad Sci 32: 8–52.

Lower Taxa

Grusonia aggeria, Grusonia clavata, Grusonia emoryi, Grusonia grahamii, Grusonia kunzei, Grusonia parishii, Grusonia pulchella, Grusonia schottii

Key

1	Flowers rose to purple; spines of fruits hairlike, flexible, antrorsely barbed (high magni- fication)	Grusonia pulchella
1	Flowers yellow; spines of fruits, when present, more rigid, retrorsely barbed	> 2
2	Major adaxial spine(s) of distal areoles terete to subterete or absent; shrubs forming mats or clumps; roots tuberlike	> 3
2	Major adaxial spines of distal areoles angular-flattened, at least at bases; shrubs forming mats; roots diffuse	> 4
3	Major adaxial spine(s) of distal areoles white to brown to black (but not rich red-brown) or absent; longest central abaxial spine commonly twisted or curved, completely chalky white (at least adaxially) except in basal 3 mm or less	Grusonia aggeria
3	Major adaxial spines of distal areoles rich red-brown (or tan); longest central abaxial spine usually straight, brownish, and cross-banded with interrupted, whitish, wavy lines	Grusonia grahamii
4	Tubercles very prominent, broad, 1-3.5 times longer than wide, not or little obscured by interlacing spines	> 5
4	Tubercles prominent, narrow, 4-6 times longer than wide, obscured by interlacing spines	> 6
5	Stem segments 7-19 × 2.5-5 cm; distal tubercles 25-50 mm	Grusonia emoryi
5	Stem segments (2-)3.5-6.5 × (1.5-)2-3 cm; distal tubercles 8-20 mm	Grusonia schottii
6	Mature fruits very spiny and glochidiate; plants to 50 cm, in series usually 2-4 stem segments.	Grusonia kunzei
6	Mature fruits not spiny but glochidiate; plants to 20 cm, in series usually 1-2 stem segments	> 7
7	Stem segments 2.5-5(-7.5) cm; distal tubercles 5-10(-16) mm; spines of distal areoles tan or white; longest abaxial spine white, daggerlike, broadly tapered; New Mexico	Grusonia clavata
7	Stem segments 5-9 cm; distal tubercles 15-25 mm; spines of distal areoles blackish or brown to tan; longest abaxial spine brown to white, narrowly tapered; Arizona, California, Nevada	Grusonia parishii