Echinocereus rigidissimus rubrispinus (LAU 088 Sierra Oscura, W. Chihuahua, MX)
This is a "must have" plant for any collection, its attractiveness is in the unique
pink and violet colour and density of its spines.
 

Photo & © copyright by Irwin Lightstone

Desription: The subspecies 'rubispinus' is a small columnar cactus with very short pink spines. When mature it will form a clump about two 60cm wide by 25cm tall.
Stems: Erect, short cylindric, only get about 7cm thick.
Radial spines: 30-35 pectinate per areole and 6-10 mm in length in red and white bands, but more ruby/violet colored compared to the 'rigidissimus' subspecies, witch makes it a very attractive cactus. This is a Mexican form and does not turn grey like the Arizona form.
Flowers: Huge up to 10cm wide. Beautiful bright pinkish-red or magenta or red with white throats. Blooms in ring on the crown of the stem in spring. The only downside is the flowers leave an unsightly scar when they drop off.
Fruit: Globose, greenish or dark purplish brownish very spiny, 3 cm in diameter, pulp white. Fruiting 3 months after flowering

Photo and © copyright by Andrea B. (Bologna, Italy)
http://www.cactusfriends.com/Andrea/index.html 
Huge 7 to 10 cm wide, shocking pink
 with white-eyed flowers.
 
 Echinocereus rigidissimus v. rubispinus
 

Cultivation: E. rigidissimus var. rubrispinus 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.

Propagation: Seeds

For this extreme macro (4x lifesize) of the interlocking spination of a cactus (Echinocereus rigidimus rubispina) I used a Canon 65mpe lens Canon 20d camerea on a tripod mounted focusing rail. Multiple exposures with different focal points were composited with Helicon software. Focusing was accomplished by advancing the focusing rail. the aperature was f8.
 
This is the most colorful form of the species and plant in cultivation are often selected for best and brightest colour.

Photo of conspecific taxa, varieties, forms and cultivars of Echinocereus rigidissimus:

• Echinocereus rigidissinus ssp. rigidissumus has stems that reach over 10 cm thick with 15-23 radial spines per areole.
• Echinocereus rigidissimus ssp.  rubispinus (Ruby Rainbow) has stems that only get about 7 cm thick with 30-35 shorter radial spines per areole. The spines are also more Ruby/pinkish colored compared to the 'rigidissimus' subspecies and are some of the showiest in the cactus kingdom.

Echinocereus rigidissimus var. rubrispinus (the varietal epithet meaning red-spined)

Scientific name:  Echinocereus rigidissimus (Engelmann) F. Haage
Published in: Special Preisverz. 13. 1897.

Synonyms: Echinocereus pectinatus var. rubrispinus

Origin:  Mexico (northern Sonora, north-western Chihuahua

Habitat: The reported habitat preference for limestone is erroneous; this species is a calcifuge, preferring soils poor in lime and usually acid.

Conservation status: Listed in CITES appendix 2.

Common Name: Rainbow cactus, Ruby Rainbow

A beautifull plant flowering or not for its beautiful
new spination which is a lacy raspberry red.

Photo and © copyright by Mladen Turcinovic (Croatia)
 

NOTE: Echinocereus rigidissimus, lacking central spines, belongs to the E. reichenbachii group, unrelated to the superficially similar E. pectinatus group, which has at least microscopically visible stubs of central spines. It sometimes occurs with E. pseudopectinatus but without evidence of hybridization.