Phyllostegia haliakalae, a member of the Lamiaceae (mint) family, is a suberect herb with forward-bending hairs on the stems. Ovate to elliptic leaves are 9 to 22 cm (3.5 to 8.7 in) long, 4 to 10 cm (1.6 to 3.9 in) wide; thin and hairy, with more hairs along veins on the lower leaf, and inconspicuously glandular-dotted. Leaf margins are rounded-toothed. White flowers are borne 4 to 6 per racemose inflorescence. Nutlets are up to 2 mm (0.1 in) long.