Plants slender and weak-stemmed, moderate-sized, flaccid and plumose in aquatic forms to more compact in emergent forms, spreading branches often con-spicuously falcate, giving capitulum a twisted appearance; green to yellow, often tinged with red, red-brown or brown in capitula. Stems green; superficial cortex of 2-3 layers, 2 layers of enlarged thin-walled cells. Stem leaves triangular-ovate, more than 1.2 mm, usually appressed; apex acute to apiculate, hyaline cells rarely septate or porose, apical region often fibrillose. Branches mostly unranked to weakly 5-ranked, often conspicuously falcate, leaves greatly elongated at distal end. Branch fascicles with 2 spreading and 2-3 pendent branches. Branch stems green, but often pinkish at the proximal ends, with cortex enlarged with conspicuous retort cells. Branch leaves ovate-lanceolate to lanceolate, 1.6-5 mm, falcate toward branch tips, when dry often undulate and recurved, rarely weakly serrulate along the margins in submerged forms, leaves from middle of spreading branches with length to width ratio less than or equal to 1:0.28; hyaline cells length to width ratio in apical convex surface region 8:1 or more, convex surface with 0-1 small round pores at apex, concave surface with faint round wall thinnings in cell apices and angles; chlorophyllous cells triangular to trapezoidal in transverse section, broadly exposed on the convex surface and exposed slightly on the concave surface. Sexual condition dioicous. Spores 29-38 µm; covered with large papillae on both surfaces, appearing pusticulate; proximal laesura less than 0.5 spore radius.
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