This heath has been regarded by many authorities as a variety of E. tetralix or a hybrid between it and E. ciliaris, but is now accepted as an authentic species. It is about 1 ft high, with its leaves in whorls of four, ovate-oblong, the margins less recurved than in E. tetralix; and thus apparently broader; usually glabrous above. The flowers are in terminal umbels as in E. tetralix-, the corolla of a deeper rosy red, shorter and broader. Seed-vessel comparatively glabrous (it is downy in E. tetralix). The only homes of this heath in the British Isles are near Roundstone (Co. Galway), where it was discovered by W. M’Alla in 1833, and in W. Donegal. It is also found in N.W. Spain, where it is equally rare and local. A pretty dwarf heath, useful for planting in broad patches as recommended for its allies.
cv. ‘Plena’. – A double-flowered form discovered in W. Galway. The urn-shaped corolla is rather wider at the mouth than in the type, and encloses several small, closely packed petals which have replaced the stamens. Superior to the type in lasting longer in flower (E. m. flore pleno; E. crawfurdii).
E. × praegeri Ostenfeld – This is the group-name for hybrids between E. mackaiana and E. tetralix. These occur where the two species are in contact in the wild and have tended to obscure the distinctiveness of the former. A form of this hybrid is usually listed as a cultivar of E. tetralix. It is a dwarf plant with pink flowers.
E. ‘Stuartii’. – This heath, collected in W. Galway in 1890, is regarded by some authorities as a hybrid between E. mackaiana and E. mediterranea but this attribution is unlikely (Heather Soc. Y.B., 1965, pp. 12-13).