Echinocereus rigidissimus Origin and Habitat: Echinocereus rigidissimus has a very wide range in USA (south-eastern Arizona, south-western New Mexico), and Mexico (northern Sonora, north-western Chihuahua). The species is abundant throughout its range.
Altitude range: 1200-2000 metres above sea level.
Habitat and Ecology: Grows on gravely hills, steep canyon sides, rocky benches in semidesert grasslands, oak woodlands, interior chaparral, mostly on igneous limestone substrates. The reported habitat preference for limestone is erroneous; this species is a calcifuge, preferring soils poor in lime and usually acid. There are no major threats for the species, however, land use change is affecting some subpopulations.
Description: Solitary (very rarely few branched)
Stem: erect, short cylindric 6 to 20 (-30) cm tall, 4-11 cm wide
Ribs: 2 18-23(-26), slightly undulate
Echinocereus rigidissimus Spine: No central spines; 16 to 22 stiff pectinate radials, appressed, straight or slightly curved toward stem, grey, reddish brown, bright pink or pink-and-white in alternating bands of colour around stem, 5- 10 mm long. Mature plants with a good light will generally have red to deep pink spines that band the stems. Each year’s growth is differentiated by differently coloured band of spines, hence the common name Arizona Rainbow.
Flowers: Bright pink with much lighter throat, 6-7 cm long, up to 10 cm in diameter. It blooms in late spring summer (May-July).
Fruit: Globose, greenish or dark purplish brownish very spiny, 3 cm in diameter, pulp white. Fruiting 3 months after flowering
Cultivation: The E. rigidissimus is not the easiest cactus to grow, but when grown well it’s very attractive. Rot easily it is sensitive to overwatering (rot prone), so perfect soil drainage is a must. It prefer a neutral to slightly acidic compost with plenty of extra grit. Best if watered with rain water and given an occasional tonic of sequestrated iron. In the summer they need an airy location in bright sun; well watered when it’s hot. To achieve the best spine colors give these plants lots of sun. In the winter light, cool, and absolutely dry conditions. Very cold resistant above approx -12C or less for short periods of time. In mild climate they grow well when planted freely outside in well-drained soil.