Homalocephala
Homalocephala is a small genus of low, flattened barrel cacti native to the southern United States and northern Mexico. Long treated as part of the sprawling genus Echinocactus, it was segregated on the strength of its squat, ribbed body, stout flattened spines and distinctive seeds, and is centred on the well-known horse crippler, Homalocephala texensis — a tough, cold-hardy plant that hunkers down almost flush with the ground.
The genus is small and its limits are still debated: some botanists sink it back into Echinocactus, while others expand it to include a handful of related species from Mexico and the south-western United States. Whichever treatment you follow, the plants share a distinctive look and a reputation for hardiness that makes them prized among growers of hardy, weather-tolerant cacti.
Description
Homalocephala species are usually solitary, unusually flattened barrel cacti — broader than they are tall — pressed low against the soil so that only the ribbed upper surface shows. The body is firm and prominently ribbed, with the ribs bearing large areoles set with heavy, rigid spines. In the type species these spines are notably broad, flattened and downward-curving, hard enough to puncture a hoof or a boot sole, which is where the common name horse crippler comes from.
Flowers appear near the crown in spring and early summer, typically pink to salmon or reddish, funnel-shaped and often fringed at the margins. They are followed by fleshy fruits that ripen a bright red and are comparatively large for the size of the plant. The seeds are large, dark and pitted — one of the characters originally used to separate the genus from Echinocactus.
Distribution
The genus is centred on the Chihuahuan Desert region and the southern Great Plains. The horse crippler ranges across much of Texas, into New Mexico and Oklahoma and the northern Mexican states, growing in open grassland, thornscrub and rocky flats. Plants tend to grow on heavy or gritty soils in full sun, often contracting down below the soil surface during drought so that they are easily overlooked among grass and stones.
Because of this ground-hugging habit and wide range through grazing country, wild plants are frequently damaged by land clearing and trampling, though the horse crippler itself remains reasonably widespread.
Notable species
- Homalocephala texensis — the horse crippler (syn. Echinocactus texensis), the type and best-known species; a flat, heavily ribbed barrel with broad flattened spines and pink flowers, and one of the more cold-hardy cacti in cultivation.
Depending on the classification followed, several related species sometimes placed in Echinocactus (such as members of the Echinocactus polycephalus group) have also been treated under Homalocephala. Because these placements are not universally accepted, growers will most often encounter the genus represented by the horse crippler alone.
Cultivation
Homalocephala are grown much as other desert barrel cacti, and the horse crippler in particular is valued for its toughness. Give plants a very free-draining, mostly mineral mix and the brightest position you can offer — full sun suits them. Water thoroughly during the warm growing season once the soil has dried, then keep them dry and cool through winter.
The type species is remarkably cold-hardy for a cactus, tolerating hard frost when kept bone dry, which makes it a candidate for unheated greenhouses and even outdoor cultivation in suitable climates. As with most heavily ribbed, ground-hugging cacti, the main risk in cultivation is rot from overwatering or from moisture sitting in the crown, so err on the side of drought. See Watering, Repotting and Pests and diseases for general technique.
Hobby and cultivar notes
Homalocephala is a collector's plant rather than a mass-market one, and it is grown mostly as the straight species from seed. Named cultivars are few; interest instead centres on well-grown, symmetrical specimens and on the plant's cold-hardiness. Because the genus is slow and forms a large taproot, plants are usually raised from seed rather than by cuttings or offsets, and deep pots suit them well.
See also
- Echinocactus — the genus from which Homalocephala was segregated
- Homalocephala texensis — the horse crippler
- Soil and potting mix · Watering · Propagation - seed · Repotting · Pests and diseases