Micrantheum demissum is a species of flowering plant in the family Picrodendraceae and is endemic to the south-east of South Australia.

Male flowers are arranged singly or in groups of up to three in leaf axils and are 1.5–2.5 mm (0.059–0.098 in) long on a short pedicel and have four sepals, the two outer ones egg-shaped, and the inner ones larger and more or less round, and there are usually four stamens but no petals.

Flowering occurs from April to October with a peak in August and September, and the fruit is an oval capsule 6–7 mm (0.24–0.28 in) long.

[2] Micrantheum demissum was first formally described in 1890 by Ferdinand von Mueller in The Victorian Naturalist from specimens collected by Ralph Tate and Johann Tepper[3][4] The specific epithet (demissum) means "low-lying" or "drooping".

[5] This species occurs on the Eyre Peninsula, southern Mount Lofty Ranges and Kangaroo Island regions of south-eastern South Australia.