Osmundea hybrida is small branchedalga which grows from a holdfast to 15mm long. The axes show a main axis with branches which may be spiral or irregular. The main axis may be slightly compressed with a medulla of cells surrounded by a cortexdeep purplish-brown in colour. A small circular pit occurs at the apex of the branches.
Spermatangial receptacles, where the malegametes occur in small cups, are at the end of the side branches. Cystocarps are spherical and sessile and tetraspores are produced in small branchlets.