Echinocereus: Rainbow and Hedgehog Cacti

ECHINOCEREUS: Medium-sized cacti with multiple ribbed columnar stems.
Common and conspicuous, but taxonomy is confusing, poorly defined, and based mostly 
on the shape, number, and color of the spines, which can be variable.
(ABOVE:  E. fendleri flowering in the Empire Mountains.)

Echinocereus rigidissimus  Arizona Rainbow Cactus
Singly or occasionally in groups on rocky slopes in desert grassland and oak woodland.  Unique stout, blunt, columnar shape.
The only cactus in its range with areoles that have NO CENTRAL SPINE.  Radial spines are flat and often downcurved.
Flowers are usually solitary.  They are light bright pink with a white center, and bloom for only one day. 

PINK FLOWERS:  E. fasciculatus, E. fendleri, E. engelmannii, E. nichollii
(Two rare and poorly-defined species from southeastern AZ, E. bonkerae and E. ledingii, are not shown here.)

Echinocereus fasciculatus
Flat, gravelly areas, gentle rocky slopes, bajadas.  Saguaro desert upland, desert grassland.
One of the most common Echinocereus.  Often abundant in suitable habitat.

Echinocereus fasciculatus
SPINES - straight, short, slender, and numerous.  FLOWERS - deep magenta to nearly purple with ragged-edged tepals.

Echinocereus fendleri
Gravelly ridges in desert grassland and oak woodland.  Tolerates higher elevations than E. fasciculatus
but may occasionally be found growing with it and/or with E. coccineus.

Echinocereus fendleri
SPINES straight, white, sometimes brown-tipped, stouter and less numerous than in other Echinocereus.
FLOWERS are bright magenta, with slightly shorter, more rounded tepals than E. fasciculatus.

Echinocereus engelmannii
Flat areas in fine gravel, saguaro desert and (more rarely) desert grassland.  May grow with E. nichollii.  At upper elevation limit, may overlap with E. fasciculatus.
Spines usually longer and thinner than in E. fasciculatus, and may be twisted or angular.  Central spines may be all white or banded with brown stripes.
Stems often thinner and more numerous than in E. fasciculatus.

Echinocereus nicholii
A Sonoran Desert species that grows among saguaros, often with E. fasciculatus and/or E. engelmannii.
Identify by relatively tall, thin stems and uniformly golden or straw-colored spines.

E. nicholii  Flowers smaller and lighter pink than other Echinocereus.
Photos of E. nichollii were taken at BLM Ironwood Forest National Monument.

RED FLOWERS:  E. coccineus
(E. triglochidiatus is found in northern Arizona.  E. arizonicus, from southeastern AZ, is not well defined for field identification and is not included here.)

Echinocereus coccineus
Desert grassland, encinal, and Madrean evergreen woodland.  Usually grows at higher elevations than the pink-flowered species, although there is some overlap.
Preferred substrate (rocky slopes, outcrops, and sheltered cliffs) is also different.  Spines are usually yellow or white, and extremely variable in density and length.
Flowers are bright scarlet, goblet shaped, with shorter, more rounded tepals than the pink species.

Echinocereus coccineus
Old plants can form mounds of several dozen stems.

Echinocereus sp.
This beautiful plant has usually long, twisted spines.  But without
flowers or fruit, further identification must remain a mystery!

Southern Arizona Botany HOME
A German site with many photos:  Echinocereus Online