It is a very distinctive plant, yet it is frequently misidentified as either G. incanum, G. canescens, or G. harveyi, none of which is shrubby, and all differ further from G. robustum in other characters. Geranium robustum is allied to G. pulchrum, which replaces it on the Natal side of the Drakensberg, though G. pulchrum possibly demands wetter sites than G. robustum.
Robust subshrub up to elm high, stems one or several from the base, becoming bare and woody there, up to ±8 mm diam., silky canescent and leafy above, erect. Stipules deeply dissected, segments linear-acuminate. Leaves all cauline, all but the uppermost petioles 2-3 times as long as the blade, with white retrorse appressed hairs, blade up to 50(-100) mm in diam., digitately (3-)5(-7)-lobed to the base, each lobe elliptic-lanceolate in outline, twice pinnatifid, the ultimate segments lanceolate, entire or with an occasional tooth, upper surface with silky silvery appressed hairs, lower thickly silvery tomentose, the hairs all of similar length. Peduncles terminal and opposite the uppermost, reduced, leaves, forming small almost leafless compound cymes clad in fine retrorse appressed hairs, spreading gland-tipped hairs often present as well; ultimate peduncles mostly 2-flowered. Pedicels up to ±60 mm long, with fine appressed retrorse hairs as well as few to many spreading gland-tipped ones. Sepals (6-)7-9 x 2.5-3.5(-4) mm, ± appressed pubescent, often with long spreading gland-tipped hairs as well. Petals (13-)18-20 x 11-12(-15) mm,obovate, shallowly notched, light purple. Rostrum with short fine spreading pubescence, often with long spreading gland-tipped hairs as well.
Dwarf shrub, 0.2-1.8 m high; robust. Stems erect, silky canescent and leafy above. Leaves all cauline, silvery, twice pinnatifid; blade up to 50-100 mm in diameter, segments narrowly ovate, margins entire, occasional toothed, upper surface with silvery appressed hairs, lower surface thick silvery tomentose; petioles 2-3 x longer than blade. Flowers: inflorescence usually 2-flowered; peduncles opposite on upper surface and terminal, pedicels up to 60 mm long, with fine appressed retrorse hairs and few to many, spreading, gland-tipped ones; petals 13-20 x 11-15 mm, light purple; Nov.-Mar.
It grows in damp or marshy ground along streams and in drainage lines. Geranium robustum favours streamsides and moist, shrub-covered mountain slopes between 1600 and 2590 m above sea level. It often forms dense stands.
Geranium robustum ranges from around Ermelo and Suikerbosrand in the south-eastern Transvaal through the low Drakensbtrg and nearby parts of northern Natal to the eastern highlands of the Orange Free State, thence through Lesotho to the Witteberg and the Cape Drakensberg as far south as the Saalboom Valley near Barkly East; Glass 505 (SAM) reputedly came from Grahamstown, but that locality is highly improbable.