Aloe hahnii differs from A. swynnertonii in the shorter bracts, pedicels and perianths. as well as flowers that are a glossier scarlet-red and more decurved It is distinguished from A. vogtsii Reynolds, with which it occasionally grows sympatrically in the central regions of the Soutpansberg mist belt, by the latter species having buds that are borne horizontally in more elongated (not capitate) racemes.
Small, slow-growing, herbaceous, succulent, perennial herb, 200-400 mm tall, with rosettes solitary, not forming clusters, 250-400 mm diam. Stems usually absent, rarely up to 120 x 40-50 mm diam., creeping along ground, with persistent dried leaves. Leaves laxly rosulate. distinctly spreading, attenuate, tapering to dried, reflexed apex, 130-400 mm long, 40-60 mm broad at base, upper surface dull pale green to brown, with pale milky green to whitish spots, variously shaped and sized, sometimes ± confluent in transverse bands, densely dotted with tiny whitish dots, lower surface uniformly pale to milky green, with dense whitish to milky green spots, ± confluent in transverse bands, usually with longitudinal darker greenish or purplish striations; margin not distinctly coloured, with very pungent, straight, brownish orange teeth, 2-4 mm long, 7-14 mm apart, ± evenly spaced; leaf exudate drying opaquely yellow, cut end eventually turning dark purple. Inflorescence single, 260-1000 mm tall, erect, 4-8(-10)-branched from above middle, upper branches rarely re-branched, branches erectly spreading. Peduncle 5-8 mm wide at base, matt purplish brown with a soft, whitish bloom, basally planoconvex; without sterile bracts; branches subtended by up to 30 mm long, 5-10 mm wide at base, straw-coloured, thin, scarious, many-nerved bracts. Racemes cylindrical to head-shaped. 40-60 x 50-70 mm, varying in size according to age of plants, larger in old plants, smaller in young plants, laxly flowered; buds erect to spreading, somewhat congested at apex, flowers subpendulous when open. Floral bracts amplexicaul, 5-15 x 2-3 mm, dirty brownish white, margins the same colour, thin, scarious, many-nerved. Pedicels 10-20 mm long, red. Flowers: perianth varying from uniformly red to tri-coloured with green, creamy white and reddish tips, 25-28 mm long, 5-7 mm across ovary, abruptly constricted to 3-4 mm above ovary to form basal swelling, widening towards middle to 5 mm, widening towards throat and wide open mouth, cylindric-trigonous; outer segments free for 12-14 mm, tips recurved and slightly spreading. Stamens with slightly flattened, pale lemon-yellow filaments, hardly exserted. Ovary 5-6 x 2 mm, bright light green; style not exserted. Fruit cylindric-oblong, matt light green capsule. 20-25 x 7-10 mm. Seed not seen. Flowering time June to July.
Aloe hahnii occurs in the mist belt regions of the Blouberg and most of the Soutpansberg in Soutpansberg and Mountain Bushveld. The altitude ranges from 1000 m in Venda to 2050 m on the Blouberg. It commonly grows on sandy soil derived from the Soutpansberg Group Quartzites. This aloe has been found in Coleochloa setifera-dominated grassland up to the margins of forests on the Blouberg and similar vegetation on the Soutpansberg, whereas in the western Soutpansberg it sometimes grows in low closed woodland in full shade.