Ptilotrichum spinosum

Shrubby perennial of the Brassicaceae family, native to the Iberian Peninsula, mainly Spain, where it is widely spread on cliffs, scree, and rocky limestone slopes of the interior, from the collinean and montane levels up to about 2,000 meters altitude. It is particularly abundant in semi-arid areas and open garrigues on limestone substrates.

It forms dense, woody hemispherical cushions, 20 to 50 cm in diameter and 15 to 30 cm in height, whose branches end in robust spines after flowering — a completely distinctive feature in the Brassicaceae family, where this type of armature is extremely rare. The foliage is small, narrow, silvery gray, densely tomentose, persistent, and gives the cushions a homogeneous ashen hue even outside of flowering.

The flowers, tiny and tetrapetalous as is customary in the family, are pure white, gathered in very numerous corymbs that completely cover the cushion at the time of anthesis, to the point of making the foliage disappear under a snowy mantle. In its natural habitat, its flowering extends from May to June depending on altitude and exposure. In cultivation, it generally blooms in May.

In cultivation, it requires absolute full sun, a very well-drained, poor, and preferably limestone soil. It perfectly tolerates summer drought and is suitable for dry rock gardens, walls, and Mediterranean gardens. Stagnant winter moisture is unfavorable to it.