Description
Petrophytum – Petrophyton – Rock Spirea –
There are about 3 to 5 species of low spreading, often mat forming subshrubs in this genus. They occur in screes or rock crevices in mountainous of Western North America. They are grown for their short, dense, spike like racemes of tiny, fluffy, cup shaped flowers, each with 5 overlapping petals, borne from early summer to autumn, and for their neat, compact habit. They form dense mats or mounds of short, prostrate, branching shoots with densely packed, smooth edged, inversely lance to spoon shaped blue gray to gray green, leathery, hairy leaves. Grow in crevices in a rock garden or scree planting, or in a tufa, or in a trough.
Grow in poor to moderately fertile, humus enriched, sharply drained, preferably slightly alkaline soil in full sun.
P. caespitosum – This mat forming subshrub from the Rocky Mountains grows 2″ tall and 12″ wide. It produces dense tufts of spoon shaped, silky hairy, bluish green leaves, to ½” long. In summer it bears tiny, cup shaped, creamy white flowers, with prominent stamens, held in conical spike like racemes, to 4″ long.
Zones 6-9
