Hypocalymma is a small genus of about 29 species, all of which occur naturally only in south Western Australia. H.angustifolium and H.cordifolium are the best known members of the genus and are widely cultivated. H.robustum is also reasonably well known but is less adaptable to cultivation so not seen as often. It is a small, spreading shrub from 1 to 1.5 metres high with linear-shaped leaves about 30 mm long. In late winter and spring the colourful pink to mauve flowers appear in clusters along the stems. Individually the flowers are about 10 mm in diameter and produce an outstanding display.
This species is a very desirable plant for cultivation because of its spectacular flowering display and compact size. It has been successfully cultivated in Mediterranean-type climates (dry summer, wet winter) but is not reliable in summer rainfall areas. The plant requires well drained conditions in full sun or dappled shade and it is tolerant of at least moderate frost. Annual pruning will help maintain a dense, bushy growth habit.
Propagation can be carried out from seed and, based on experience with the related H.angustifolium, improved germination may be achieved using smoked water. Propagation from cuttings is the preferred method and cuttings strike readily from hardened, current season’s growth. H.robustum would be a good candidate for grafting experiments possibly using Darwinia species as rootstock.
Photo: Tony Cavanagh