Pediocactus

A small cactus of limestone areas in northern Arizona. During drought, its roots shorten and draw the stem underground. Thirty-one years of observations linked this phenomenon with plant size, survival and reproduction.

S.L.Welsh & Goodrich

Hochstätter

(Hochstätter) Hochstätter

One of the smallest members of the genus. Short, radially arranged spines shelter a stem whose diameter usually falls within a few centimetres. Natural sites are concentrated in northern New Mexico. The species has been the subject of long-term observations and population-restoration experiments.

Pediocactus nigrispinus grows in the northwestern United States. Long, dark central spines surround a stem consisting of distinct tubercles. Studies of basalt sites combined habitat description with measurements of fruiting, adult-plant survival and lack of observed recruitment in several plots.

Pediocactus paradinei is distinguished by long, flexible spines forming a pale covering over the stem. It is associated with limestone substrates of the Kaibab Plateau in northern Arizona. New studies assess changes in surrounding vegetation and future availability of climatically suitable habitats.

A small cactus of Arizona and southwestern Utah with thick, pale spines of corky structure. Former subspecies differed in features including stem size and areole spination. Comparison of many populations showed continuity of this variation and its partial association with plant size.

Pediocactus sileri grows on gypsum deposits along the Arizona–Utah border. Numerous spines at the stem base form a covering in contact with the fine substrate. Yellow flowers with purple veins and large, wrinkled seeds are among its characteristic features.

Pediocactus simpsonii has an extensive range in the western United States and reaches high-altitude grasslands and coniferous forests. Spherical stems bear numerous short radial spines and longer brown central spines. Flowers develop in spring or early summer.

A small Utah cactus with densely woolly areoles and short, pale spines. In spring, the plant emerges, flowers and produces seeds, then may hide in the substrate again. Twenty years of observations on one plot demonstrated the importance of large flowering specimens and the effects of repeated trampling.