Four species of Echinocactus live in the Chihuahuan Desert, only two of which appear in the Trans-Pecos – the Eagle-Claw Cactus (Echinocactus horizontalonius) and Horse-Crippler (Echinocactus texensis).
You can easily recognize them on sight.
Eagle-Claw Cactus (Echinocactus horizontalonius)
The Eagle-Claw or Turk’s Head cactus is common throughout the Big Bend region. It grows on any soil, including soils high in gypsum. Eight ribs support widely spaced areoles producing 1–3 lower central spines, predominately cross-ribbed, plus 2 upper-central spines that are much smaller. Five radial spines typically curve down towards the cactus’ body. Areoles are widely spaced, and the cactus’ flesh is plainly visible though that condition does not seem to attract many herbivores.
Dense wool-like trichomes cover the stem apex; the trichomes shrink as they age, but they are annually renewed just before blooming. The flowers are magenta or bright rose-pink. Flowers may appear between April and June; after rains between July and September, the plant may bloom again
Horse Crippler (Echinocactus texensis)
Horse cripplers live in the eastern part of Brewster County, extending east beyond the Pecos River and north beyond the Trans-Pecos. They are uncommon-to-absent in most of the Big Bend, but appear briefly in the state park.
Horse Cripplers grow singly. The stem is severely depressed and may withdraw to below ground level when dry. However, with good rains, the stem may swell to a few inches in height. Mature plants always have 13–27 ribs with sharp crests. White wooly trichomes cover the apex. Each areole has one central spine and usually 6 or 7 radials. The central spine can grow to 2 inches long and have a fierce appearance.
Here is a photo that shows how depressed the stem can be.
And here is one after some good rains.
This cactus blooms in April and May, opening in late morning and remaining open until late at night. The blossoms are smaller and paler than those of the Eagle Claw. Small mammals enjoy dining on the flowers, so finding one in pristine condition can be a challenge.
Fruits are bright scarlet maturing at ½ to 1 inch. Mature fruits can persist on the plant for months, but animals have usually eaten then before long.
The plant is exceedingly tough. You, and even your horse can step on it without harming the plant. However, the spines are tough enough to pierce just about anything that steps on them.