Perennial of the Caryophyllaceae family, Arenaria hookeri is native to the great plains and rocky foothills of western North America, from Wyoming to Nebraska and Colorado, where it grows in dry prairies, rocky outcrops, and exposed gravelly slopes, at altitudes of about 1,500 to 2,500 meters.
It forms a very dense, hard, and spiky cushion, dark green in color, composed of rigid, linear-needle-like leaves with mucronate tips, tightly packed in imbricated rosettes that give the tuft a characteristic bristly texture. This spiky cushion habit is a remarkable adaptation to the windy and dry conditions of its natural habitat, and is enough to identify the species even when not in bloom.
The flowers, clearly visible in the photo, are white, with five relatively broad oval petals, borne on short peduncles that barely emerge above the cushion. The well-marked green sepals form a prominent, ribbed calyx that contrasts with the whiteness of the petals. In its natural environment, flowering extends from May to July. In cultivation, it generally occurs in May-June.
It requires full sun, perfectly drained, poor, and rather dry soil, preferably gravelly or sandy. It does not tolerate stagnant moisture, especially in winter. A plant of character for a well-tended alpine rock garden or pot culture.