P. nitida is most closely related to P. caffra. They constitute a pair of vicarious species, both variable and both widespread, yet each being separated, geographically and climatically. Typically, the waboom is a small gnarled tree up to 5 metres with a whitish trunk up to half a metre in diameter and a rounded to irregular crown of greyish-white foliage. At the other extreme, there are dwarf, multiple stemmed races of P. nitida, in which a single main trunk is not developed. Moreover, their leaves are narrower than usual, oblong in form with a greener, olivaceous tint rather than whitish-glaucescent. These dwarf, multiple-stemmed races have been recorded from Kanonkop in the Tygerberg Hills, near Red Hill on the Cape Peninsula, on the Langeberg at Montagu and Swellendam, and on the hills near Albertinia. Although they were once recognised at varietal level and even as a distinct species at one stage under the name P. reticulata, their random occurrence and gradual merging.
Tree 5-10 m or dwarf form < 1 m, resprouting from base or trunk. Leaves elliptic, grey-glaucous. Flower heads cup-shaped, involucral bracts short, silver-grey, sometimes silky, style 60-80 mm long.
Shrub or tree of variable height, spread and branching; usually a small gnarled tree to 5 m in height with a trunk diam. up to 400 mm, sometimes attaining 10 m in height with a trunk diam. up to 1 m; bark thick, whitish grey; occasionally a low multiple stemmed shrub to 1 m tall with a persistent rootstock. Stems stout 6-10 mm in diam., glabrous. Leaves sessile, oblong, elliptic to broadly elliptic, or obovate, acute to obtuse, glabrous, dull olivaceous to heavily glaucescent, coriaceous, 80-180 mm long, 15-60 mm wide. Inflorescence 80-160 mm in diam., oblong in bud, perianths projecting beyond involucral bracts; becoming globose on opening; expanded styles projecting beyond involucral bracts. Involucral receptacle conic-depressed, acute, 20-30 mm in diam., 15 mm high. Involucral bracts 5-6 seriate; outer series very broadly ovate, acute or obtuse, 10-15 mm long, 10-15 mm wide, tightly imbricate, glabrous to silvery or minutely ferruginously sericeous; inner series widely splayed, oblong, 30-45 mm long, 10-20 mm wide, glabrous to partially sericeous, slightly incurved, apices rounded, concave. Perianth 60-75 mm long, slightly adaxially curved, glabrous except for the sericeous to velutinous perianth limbs; tube 10-15 mm long, glabrous, enlarged and prominently ridged, inner surface of lips occasionally minutely puberulous; claws slender, glabrous; limbs linear, straight, acute to acuminate, 20-28 mm long, silvery sericeous to densely velutinous. Anthers 4, sessile. Style adaxially arcuate, 60-80 mm long, broadened and ancipitous proximally, terete and tapering distally, glabrous. Pollen presenter filiform, straight, not clearly differentiated from style, 10-12 mm long. Ovary obconic, 3-5 mm long, covered with 10 mm long, straight tawny trichomes. Hypogynous scales broadly ovate, 2 mm long, thick and fleshy. Flowering may be erratic, occurring almost throughout the year but there is a distinct winter peak, between May and August.
P. nitida occupies a diversity of habitats. The extremes range from rocky coastal shore-line at sea-level where it is battered by wind and drenched in salty wave-spray, to high interior mountain ranges at 1200 metres, there to be dusted by winter snows. Mostly, however, the waboom favours rocky talus slopes at lower or middle levels. It is virtually absent at elevations above 1200 metres. This species is almost invariably found on Table Mountain Sandstone but occasionally grows on weathered Cape Granite, or in a few localities, on Malmesbury Shale. The waboom is particularly associated with the drier mountain ranges of the south-western and southern Cape, selectively preferring warm, well-drained sites on northerly, easterly or westerly slopes. P. nitida does occasionally occur on the moister southerly slopes of the coastal ranges, but it is definitely uncommon there. Rarely solitary, it usually forms quite extensive populations of more or less evenly spaced individuals, growing in a low open woodland formation.