Stems cylindrical, sometimes some of the upper ones slightly flattened, 1-1.5(-2) dm long, all stems similar in width, second internode 6-15(-20)
mm long, 1.5-2.5(-3) mm wide, others usually 8-15 mm long, 1.5-3 mm wide, nerves inconspicuous. Axils distichous.
Flower groups at first opposite and confined to the axils, later often forming a continuous band around the stem.
This species is very closely related to Korthalsella remyana; the only character that consistently separates them is the axil arrangement, which is distichous in K. cylindrica and decussate in K. remyana.