Osmoxylon mariannense is a spindly, soft-wooded tree to 10 m (33 ft) in height. Ascending, gray-barked branches bear leaf scars. Leaves vary in size, are palmately-lobed, 30 cm (12 in) long and 50 cm (20 in) wide. The 7 to 9 lobes are coarsely toothed and have a depressed mid-vein. Leaves are alternate or whorled at the branch tips. Petioles are 35 to 40 cm (13.8 to 15.7 in) long in conspicuous green multiple “sockets.” Yellow flowers are in branched, terminal cymes or umbels. Maroon fruits are fleshy, round, pea to small grape sized.