Stems 25+ cm diam., widest where proximal branches arise; pith 10+ cm diam. Flowers usually ter-minal, 6.5-8.5 cm diam.; scales on flower tubes broadly triangular to rounded, green with red apices; ovary with locule to 25 mm; filaments white, short; anthers tan. Seeds: testa thin. 2n = 22. Flowering early May-late Jun. Sonoran desert scrub; 180-1400 m; Ariz., Calif.; Mexico (Sonora). In its habitat Carnegiea gigantea, the saguaro (also spelled sahuaro), is the most conspicuous and most-studied of all North American cacti. It is the tallest cactus of the flora---indeed, these are the tallest trees of the deserts in the United States.

Plant: Massive columnar trees to 15+ m tall. STEM simple or the trunk bearing 1-6(-20+) upright-curving branches usually 2-2.5 m above ground, commonly in subwhorls, sometimes rebranched, to 75+ cm in diameter (widest at lowest branches), green, glabrous but woolly at apices; ribs 12-24, 3-4 cm high, continuous, increasing in number from the narrow base. AREOLES mostly circular, 6-8 mm in diameter, spaced about 2.5 cm apart on rib to nearly contiguous at stem apices, bearing short tan to gray wool Leaves: LEAVES of long shoots minute or obsolete; SPINES yellow to reddish brown, aging gray to gray-black, terete to angular, mostly bulbous-based, divergent; central-most spines stout, 3-5(-10) per areole, mostly l-3 cm long, but the basal one longest, 3.5-5(-8) cm long; peripheral spines finer, 12-15(-19) per areole, 1-2 cm long Flowers: nocturnal but remaining open into morning, solitary in areoles, arranged in masses usually on south sides and below apices of the branches, perfect, actinomorphic, funnelform, (8-)10-12 cm long, 4-6 cm wide; ovary ovoid, bearing fleshy, elliptic scales, these ca. 2 mm long, apiculate, with axillary tufts of short white wool; floral tube scaly, ca. 6 cm long; outer tepals green; inner tepals waxy-white (drying black), reflexed, broadly obovate, ca. 2.5 cm long, apiculate; stamens numerous, exserted, the filaments and anthers cream-white; style and the ca. 12 stigma lobes cream-white Fruit: FRUITS maturing pale red, glabrous, scaly, spineless, ellipsoid to obovoid, 4-8 cm long, splitting longitudinally into 2-4 irregular radiating portions; pulp bright red, juicy, sweet. SEEDS numerous, deep red-brown appearing black, finely pitted, ca. 2 mm long, 1.8 mm wide Misc: Upper Sonoran Desert zone, especially on hills and buttes; below 1600 m (5200 ft); May-Jun, occasionally in Sep REFERENCES: Pinkava, Donald J. 1995. Cactaceae. J. Ariz. – Nev. Acad. Sci. 29(1): 2, 6.