Argyroxiphium kauense is a rosette shrub, usually single-stemmed, its vegetative stems about 3 to 70 cm (1 to 24 in) long, and flowering stems about 0.7 to 2.5 m (2 to 8 ft) long. The leaves are very narrowly sword-shaped, 3- to 4-angled in cross section, about 20 to 40 cm (8 to 16 in) long and 0.5 cm (0.2 in) wide at the middle, nearly covered with dense, silky, silvery gray hairs. The flowering stalk as many branches, each with a flowering head of 3 to 11 ray flowers each about 1 cm (0.4 in) long, and 50 to 200 disk flowers each about 0.6 cm (0.2 in) long. The fruits are dry and black.