The needle-like, spiny leaves of Aptosimum spinescens are linear or narrowly oblanceolate, sometimes channelled with rounded or acutely pointed tips. The margins are entire, the leaves up to 2,5 cm long. They cover the branches densely in rosette-like branchlet tips.
Tubular blue or blue-violet flowers grow solitary from leaf axils. The five rounded petal lobes that spread to a diameter of 7 mm around the flower mouth are blue with dark patches and lines near the base. The outside of the corolla tube is pale yellowish tan with equally spaced dark, longitudinal lines from lobe to base.
The four stamens growing in unequal pairs are included in the tube, the whitish style visible in the throat.
Flowering happens from late winter or spring to summer or early autumn (Shearing and Van Heerden, 2008; Le Roux, et al, 2005; Bond and Goldblatt, 1984; iNaturalist).