Greek keras, hom, + pteris, fern, alluding to the antlerlike fertile fronds.

Plants medium-sized, rooting in mud or free-floating, succulent. Rhizomes compact, obscured by succulent, fibrous roots, with few thin scales. Fronds clustered, dimorphic, to 50 cm long, glabrous, fertile fronds longer than sterile ones, vegetative fronds erect or spreading. Stipes fleshy and succulent, green. Blades pinnatifid to 4-pinnate, triangular-deltate, young blades with wide pinnae and ultimate segments, buds at distal margins of pinna stalks. Pinnae alternate, sterile pinnae deeply pinnatisect, fertile pinnae longer and narrower than sterile pinnae, small, lighter green, dormant bud initials in sinuses sometimes developing into plantlets. Ultimate segments linear, obliquely arranged, sterile segments 2+ mm wide, fertile segments longer and narrower, sharply lobed, less than 1.3 mm wide. Veins anastomosing, forming areoles. Sori in marginal rows on narrow pinnae. Indusia formed by recurved pinna margins, thinner textured than blade.

A genus of three or four species in tropical, subtropical, and warm-temperate regions of the world. Represented in Hawai 'i by a single naturalized species.