Justicia adhatodoides flowers are very attractive, growing in dense racemes. A small green calyx with pointed lobes is at the flower base. The corolla of the flower has two lips with the upper one hooded over the flower's lower parts. A part of the lower lip has a number of magenta to purple lines (or dotted lines) along its length. Blooming happens from the end of summer through winter.

Carpenter bees do the pollination. Mrs M.E. Barber, whose name is remembered in Aloidendron barberae, previously Aloe barberae, wrote an article in 1871 for the Journal of the Linnean Society describing the performance of these bees on the flowers of the pistol bush, as the plant is commonly known (Coates Palgrave, 2002; www.plantzafrica.com).