Pediocactus bradyi

Name and range

Pediocactus bradyi is an accepted species endemic to northern Arizona. It formerly also appeared under the names P. simpsonii subsp. bradyi, Puebloa bradyi and Toumeya bradyi. These names refer to the same species in the POWO treatment adopted here. [2-WWW]

A small stem and short spines

The stem is usually solitary, hemispherical or obovoid. Flora of North America gives a height of 3.2–6.2 cm and width of 2.5–5 cm. Woolly, elliptical areoles mostly have 13–16 short radial spines, 3–5 mm long. Central spines are usually absent. Flowers are straw-yellow and reach 1.5–3 cm in diameter. The fruit turns from green to reddish brown and dries. Dark seeds have a papillose, wrinkled surface. [Heil and Porter 2003a, Flora of North America, P. bradyi]

Limestone ledges and the cycle of stem appearance

The floristic description places sites on clayey ledges with limestone gravel, at elevations of 1000–1200 m above sea level. Flowering occurs in early spring. As the substrate dries, roots contract, pulling the stem below the surface. Re-emergence occurs after moisture conditions improve. [Heil and Porter 2003a, Flora of North America, P. bradyi. Rojas-Pimentel et al., pp. 1–3] [Rojas-Pimentel et al. 2026, Flora of North America, P. bradyi. Rojas-Pimentel et al., pp. 1–3]

The study linked root contraction and later elongation to transitions between two plant states, visible above the surface and hidden underground. Conclusions concern the fates of marked specimens. The study included neither microscopic analysis of cells responsible for root shortening nor direct temperature measurements of hidden stems. [Rojas-Pimentel et al. 2026, pp. 2–4]

Thirty-one years of observations

The model published in 2026 used data from 965 plants on three study plots near Marble Canyon. The dataset was described as covering 1988–2019. The analysis included diameter, survival, growth, flowering, new plants, transitions into the hidden state and re-emergence. Roots contracted mainly in small specimens. Larger plants had higher probabilities of survival and flowering, while diameter growth weakened above around 35 mm. [Rojas-Pimentel et al. 2026, pp. 2–6]

The first flowering cases were recorded in plants only 10 mm in diameter. In this sample, that represented a particular small plant attaining reproductive capacity. Diameter alone does not determine its age. Large specimens usually contributed more to flower production and had a lower probability of becoming hidden than small ones. [Rojas-Pimentel et al. 2026, pp. 4–6]

Individual plant survival and population growth rate

The mean model gave very similar long-term population growth coefficients with root contraction included and with this transition removed. Model elasticity was greatest for stem survival and growth. Root elongation allowing emergence from the hidden state contributed more than entry into that state itself. The model assumed zero mortality while hidden, although two deaths of such plants were recorded in the material. The result also depends on this simplification. [Rojas-Pimentel et al. 2026, p. 3–7, tab. 2]

A separate climatic analysis published in 2014, based on 22 years of data, indicated declining abundance in a model incorporating random variation in conditions between years. It yielded λs = 0.961. Growth rate was associated with winter precipitation and temperature. This is a different model and averaging method from the 2026 projection. [Shryock et al. 2014, abstrakt publikacji, 22-letnia seria danych]

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