There are several species of Erica that exhibit a considerable variation in colour and E. mammosa is an excellent example of such a species. It is in fact variable in all respects. In the common form the flowers are dark red or orange-red and are closely packed in small inflorescences. Other less common colour forms that have been recorded are orange, pink, purple-pink, green, cream, white and even with pink tips. In many of the latter forms the inflorescence tends to be more lax. In this treatment of the species the inclusion of E. gilva Wendl. under E. mammosa by Salter has been followed. He states: CA robust cream-flowered form with broader sepals, growing in a few places high on Table Mtn., Devil's Peak and Constantiaberg, has been named E. gilva Wendl., but there appear to be no reliable characters to justify its separation.' This form appears to be confined to the Cape Peninsula. In the section Pleurocallis, E. mammosa is easily distinguished by the possession of four dents or furrows at the base of the corolla. This also occurs to some extent in E. nevilki L. Bolus and E. quadrisukata L. Bolus, two species endemic to the Cape Peninsula, but their general appearance and habit are completely different.
Erect shrub up to about 1.2 m (4 ft). Branches numerous in favourable conditions, puberulous, leaves 4-nate or scattered, 6-10 mm long, erect-spreading, linear-lanceolate, trigonous. Flowers in a tight or loose raceme, cernuous; peduncles 2-4 mm long, usually puberulous; bracts median, small. Sepals long, obovate or ovate-lanceolate, acutely keel-tipped, scarious. Corolla 1.5-2.5 cm long, tubular, obliquely inflated, with 4 dents or grooves at the base, glabrous, variously coloured as above; lobes erect, rounded. Filaments filiform; anthers included, 2 mm long, lateral, oblong or cuneate usually with a sharp basal point in front, appendiculate; awns of variable length. Ovary glabrous; style shortly exserted; stigma capitate.