The closest ally to P. transvaalensis is P. angolensis which has a characteristic inflorescence structure with many inflorescence units contracted into an axil, and an occasional inflorescence unit with a very long peduncle. In contrast, the inflorescence units of P. transvaalensis are not contracted into the leaf axils. The broader tertiary bracts of these two species serve to separate them from the other species of Peristrophe in southern Africa. P. transvaalensis has a marked vestiture of multicellular uniseriate eglandular trichomes, which imparts a grey-green colour to the leaves of living plants; this feature is very unusual in this section of the genus. Conservation status: P. transvaalensis is not a common species and is known from only six gatherings from a relatively restricted area and populations of the plant are sparse. The conservation status of this species requires urgent investigation.
Evergreen suffruticose perennial up to 1 m high. Leaves ovate to narrowly elliptic, acuminate, attenuate at base, 26-41(-42) x 8-13(-14) mm, with many multicellular eglandular trichomes and cystoliths; petiole (1.7-)2.0-4.3(-4.6) mm. Inflorescence of monochasial cymes (inflorescence units), (1 or 2)3(4) umbellately arranged, sometimes compounded; inflorescence axis (4.0-)4.2-7.0(-7.4) mm long; longest peduncle of inflorescence units (2.4-)4.1-12.9 mm long. Bracts: secondary bracts 2, free, lanceolate, (4.7-)5.1-6.6 x 0.6-1.0(-1.1) mm, pubescent, sessile; tertiary bracts oblanceolate, unequal, larger one (13.6-)13.8-16.1(-16.4) x (0.4-)0.6-1.1(-1.5) mm, almost tomentose, trichomes multicellular and eglandular. Calyx: tube 1.5 mm deep; lobes, lanceolate, 5.5 mm long, margins membranous and ciliate, with small glandular trichomes on outer surface. Corolla: tube (7.3-) 7.5-9.0 mm long, sericeous to tomentose; lip in lower position ovate, (7.1-)8.8(-9.0) x 2.0-2.7 mm; lip in upper position narrowly elliptic, 7.0-8.4(-8.8) x (-3.6) mm; light purple with dark purple honey-guides on white background on lip in upper position. Stamens: filaments with short and long multicellular eglandular trichomes, white; anther thecae superposed, purple. Disc shallowly cupular with crenate top and 2 short stubby awns. Gynoecium: stigma shortly bilobed; style sparsely strigose; ovary ovoid, sparsely pubescent. Fruit pubescent, 9.0-10.1 x 2.1-2.5 mm. Seeds 2.0-2.2 x 1.8-2.0 mm, rough and tuberculate. Flowering time: in the field the plants were beginning to flower in January, and were flowering profusely when revisited in May, whereas the plants in cultivation were still in flower in August of the same year. It appears that the species flowers throughout the year, but more profusely in winter.
Scrambling, trailing or decumbent suffruticose perennial, several-branched from a woody rootstock, to 1 m long, sometimes rooting at nodes of trailing portion; stems 6-angular, pale-ridged, with rather dense pale spreading or retrorse eglandular hairs. Leaves sometimes immature at flowering, lanceolate or narrowly ovate, 2.3-5 x 0.4-1.3 cm, base cuneate or shortly attenuate, apex acute, apiculate, surfaces pale-pubescent, particularly on veins beneath and midrib above; lateral veins 4-5 pairs; petiole 2-7 mm long. Inflorescence axillary, 1(2) umbels of (1)2-4(5) cymules per axil, umbels often partially compounded; umbel peduncle 4-32 mm long, umbels in uppermost axils rarely sessile; main axis bracts linear-lanceolate, 4-9 x 0.5-1 mm, those of lowermost umbels on stems sometimes more leafy and lanceolate, to 13 x 3 mm; cymules pedunculate, usually with peduncle of one cymule much longer than others, (2)5-32 mm long; cymule bracts green or smaller of pair turning brown, pairs ± highly unequal, ratio 1.25-1.9:1, larger bract subulate or slightly oblanceolate, (9)12-18 x 1.5-3(3.5) mm, apex mucronulate, external surface pale spreading-pubescent throughout, only midrib prominent, margin pale-hyaline in lower half; bracteoles as cymule bracts but lanceolate, 8-10.5 x 1.5 mm. Calyx lobes 5-6 mm long, with or without few minute glandular hairs, margin hyaline, ciliate. Corolla 17-20 mm long, pink to mauve with purple guidelines, pubescent externally; tube 7-9 mm long; lip held in upper position narrowly oblong, 8-11 x 2.5-3.5 mm, palate puberulous towards mouth; lip held in lower position ovate or elliptic, 8-11 x 5.5-8.5 mm. Staminal filaments 4.5-7 mm long, pubescent; anther thecae 0.7-1 mm long, superposed. Style sparsely strigulose or glabrous. Capsule 9.5-11 mm long, pale eglandular-pubescent; placental base inelastic. Seeds c.2 mm in diameter, sparsely tuberculate mainly around rim, tubercles shortly clavate.
Interface of Acocks's Sourish Mixed Bushveld and Sour Bushveld (now Mixed Bushveld and Waterberg Moist Mountain Bushveld).
Open bushland and woodland, e.g. Terminalia, Combretum, Croton, on rocky hillslopes and river valleys.