Mammillaria macdougalii

Plants unbranched, deeply seated in substrate. Roots short, obconic taproots; secondary roots diffuse. Stems usually flat-topped (in old age or under dense brush hemispheric), 4–20 × 9-25(–30) cm, firm; tubercles 10–17 × 6–8.5 mm; axils woolly, wool 5–8 mm, bristles absent; cortex and pith not mucilaginous; latex sticky white, abundant in healthy tissue throughout cortex of stem, tubercles, and sometimes flower receptacles. Spines 11–14(–16) per areole, white to straw yellow, glabrous; radial spines 10–12 per areole, whitish to pale yellowish tan, needlelike, 20 mm, stiff; central spines 1–2(–4) per areole, ± porrect or 1 ascending and 1 descending, straight or slightly curved, 10 mm; subcentral spines 0. Flowers 3–4 × 2.5–3.5 cm; outermost tepal margins densely minutely fimbriate (at 10×); inner tepals greenish white to greenish yellow, 14–17(–25) × 2–3 mm; stigma lobes yellow-green to pale green, 2–3 mm. Fruits whitish green proximally, pale green distally with pale rose-purple on sunlit portions, obovoid to clavate, 15–26 × 7.5–15 mm, juicy only in fruit walls; floral remnant persistent. Seeds reddish brown or orange, 1.1–1.3 × 0.9 × 0.8 mm, pitted; testa intermediate, anticlinal cell walls undulate, interstices much narrower than pit diam., pits deeply concave, elongate. 2n = 22.

Phenology: Flowering Mar–May; fruiting Oct–Mar.
Habitat: Rocky slopes and ridges, ecotone between Sonoran desert scrub and chaparral, oak woodlands, grasslands
Elevation: 1100-1800 m

Ariz., Mexico (Sonora).

Discussion

Mammillaria macdougalii is the characteristic flat-topped mammillaria of the mountains near Tucson and Nogales, Arizona. Records from farther east are all (insofar as can be determined) misidentifications of M. heyderi var. bullingtoniana.

Selected References

None.

Lower Taxa