Fronds free floating, broadly ovate to orbicular, dorsal surface greenish, sometime reddish brown, asymmetrical, slightly convex, 2-7 x 2-4 mm, mostly hemispherical and strongly swollen below with large inflated hyaline cells and air spaces and usually with 40-50 meshes and with 3-5 veins; new fronds budding laterally and remaining attached to very short stipes. Flowering cavity lateral, spathe enclosing 2 staminate and 1 pistillate flower. Fruit 1-5-seeded and winged; seed ribbed, utricle rounded.