Eriosema umtamvunense is an erect perennial shrub, up to 500 mm high, with a horizontal, branched rootstock. The stems are densely covered in reddish yellow hairs, but less densely towards the base. Up to 20 stems are produced, usually branching from lower nodes. Leaves are trifoliolate, with 3, short-stalked leaflets. Terminal leaflets are 57–70 × 28–40 mm; side leaflets are smaller. The upper surface is dull green with fine long hairs, lower surface finely woolly, grey to white, with longer reddish yellow hairs on the primary veins, and small yellow glands visible. Both the terminal and side leaflets have a prominent hairy midrib above.

Inflorescence is a raceme, about 125 mm long, elongating as it matures. Up to 25 flowers are clustered in the upper part; bracts are short, up to 8 mm long and dropping soon.

Flowers are large, up to 13–14 mm long, bright brick-red and yellow; the calyx covered in golden hairs. They are typical papilionoid (butterfly-like) pea flowers, with a standard, wing and keel petals. Flowering time is in early summer, from Nov.–Dec.

The fruit is a pod, 15–16 × 10–11 mm, densely covered in long, golden hairs lying flat against the surface.

This species has consistently been confused with E. squarrosum, E. dregei, E. latifolium and E. luteopetalum. It differs from all of these species in its red and yellow flowers and golden-haired calyces, whereas the last-named species all have yellow flowers and silver-haired calyces. From E. preptum it can be separated by its much larger flowers and fruits and by the wing petals exceeding the keel petals.