Pediocactus winkleri

Name and structure

Pediocactus winkleri is an accepted species in POWO, native to Utah. The names P. bradyi subsp. winkleri and P. bradyi var. winkleri are its synonyms. [2-WWW]

The stem is usually solitary, reaching 3.9–6.8 cm high and 2.7–5 cm wide. Areoles are elliptical or circular, with dense wool. Spines are exclusively radial, 8–14 per areole, white or light brown and short, 1.5–4 mm long. Flowers are peach-coloured or pink, 1.7–3 cm in diameter. The fruit dries and turns brown. Seeds are black, glossy and wrinkled. [Heil and Porter 2003a, Flora of North America, P. winkleri]

Substrate and growth season

The species occurs on rocky surfaces containing gypsum, gravel and fossil shells, at elevations of 1500–2100 m above sea level. Long-term observations took place in Capitol Reef National Park at 1823 m. One 10 × 10 m plot covered sparsely vegetated deposits of the Morrison Formation, with gravel and basalt rocks. [Heil and Porter 2003a, Flora of North America, P. winkleri. Clark et al., pp. 89–91] [Clark et al. 2015, Flora of North America, P. winkleri. Clark et al., pp. 89–91]

In this population, plants appeared above ground in spring, flowered from April to mid-May and produced seeds in June. After this period, stems withdrew into the substrate. Some remained invisible for subsequent seasons, which was recorded in their individual identification histories. [Clark et al. 2015, pp. 89–92]

Slow stem enlargement and concentrated reproduction

From 1995 to 2014, a total of 107 plants were marked. During tracking, 86% showed no diameter increase or an increase of less than 1 cm. On average, around 28% of plants produced reproductive structures in a given year, meaning buds, flowers or fruits. Ten specimens produced 31% of all recorded flowers. Long-lived, larger plants therefore contributed substantially to potential reproduction on this plot. [Clark et al. 2015, pp. 92–98]

In 1995, 44 living plants were recorded. In 2014, 31 living plants were visible, while five more had an uncertain status and had been alive at the 2013 census. This record reflects the distinction between confirmed death and temporary invisibility. Annual counts of above-ground stems alone do not include the full history of marked plants. [Clark et al. 2015, pp. 92–96]

Hoof marks and weather fluctuations

Signs of disturbance by large hoofed mammals were recorded near 74 of the 107 tracked plants. Of 205 events classified in this analysis, 190 were attributed to livestock. The model linked trampling to increased odds of death and decreased odds of flowering. Repeated disturbances over several years mattered more than a single mark. [Clark et al. 2015, p. 91–96, ryc. 3–4]

Weather relationships changed between seasonal stages. Higher minimum temperatures in February and March were positively associated with the appearance of new plants, while high April maximum temperatures were associated with mortality. Rainfall over the preceding twelve months affected flowering. These are statistical relationships from one plot observed for twenty years. [Clark et al. 2015, pp. 94–99]

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