2n = 28

Perennial mat-forming herb, aquatic to terrestrial, stems green, erect or prostrate, 2-10(-15) cm long, rooting at lower nodes, usually ± unbranched apart from rhizomatous portions at base. Leaves all entire, linear, 2-6 mm long, 0.5 mm wide, decussate, tip blunt to acute, sometimes almost acuminate, usually with a ± well defined midrib. Hydathodes 0-2. Inflorescence a terminal spike with the flowers borne singly in axils of the upper leaves which are indistinguishable from the other leaves. Each flower subtended by 2 bracteoles which are deltoid, 0.6-0.7(-1.3) mm long, 0.2-0.3mm wide, acuminate. Flowers unisexual, males and females often borne on separate stems, but if together, then males borne in upper axils, females below. Male flowers 4-merous, sessile or on pedicel up to 1 cm long. Sepals 4, (ob)lanceolate to narrowly (ob)ovate, 0.9-1.4 mm long, 0.3-0.5 mm wide, acute or obtuse, sometimes shortly mucronate, margins entire or minutely denticulate, Petals 4, red, hooded, weakly keeled, 1.3-1. 7(-2.5) mm long, 0.8 mm wide, reflexed at anthesis. Stamens 8; filaments short, lengthening to 2.5 mm at anthesis; anthers linear-oblong, 0.9-1.1(-1.6) mm long, 0.4 mm wide, 4-locular, shortly apiculate. Styles and ovary 0. Female flowers 4-merous, on pedicel 0.2-0.5(-1.0) mm long. Sepals 4, deltoid, 0.2 mm long, 0.2 mm wide. Petals 0. Stamens 0. Styles 4, alternating with sepals, 0.4 mm long, stigmas fimbriate, white, sometimes grading to pale pink. Ovary obpyriform, 0.6 mm long, 0.5 mm wide, channelled opposite sepals, 4-locular. Fruit sessile or shortly pedunculate, red-purple, ovoid to obpyriform, 1.0-1.5 mm long, 1.1-1.2 mm wide, deeply channelled opposite sepals, smooth to weakly striated, not verrucose; sepals usually persistent, membranous, 0.2 by 0.2 mm; styles persistent, becoming reflexed. Fruit splitting at maturity into 4 single-seeded mericarps. Mericarps ± globular with attenuate neck formed from persistent style.

Planta valde similaris subsp. pedunculato, sed in fructu laevi et stigmatibus albis ad roseola differt.