Plants grasslike, heterosporous, perennial lycophytes growing as submerged aquatics or emergent and amphibious [or seasonal terrestrials]. Rhizome brown, cormlike, corky, (2 or)3(-5)-lobed, nearly globose [or horizontally spindle-shaped and proliferous]. Roots arising along central groove separating each rootstock lobe, dichotomously branched [or unbranched], containing eccentric vascular strand and surrounding lacuna. Microphylls tufted, several to many, erect to spreading, straight to recurved, (1-)5-50(-100) cm, spirally [or distichously] arranged, simple, linear with membranous margins toward base, dilated and spatulate basally, tapering to apex, semiterete in cross section with adaxial surface flattened and abaxial surface rounded, containing 4 transversely septate longitudinal lacunae with septa apparent on adaxial microphyll surface, 1 central collateral vascular strand, and frequently several peripheral fibrous bundles at microphyll angles. Ligules deltoid to cordate, 1-2(-6) mm, membranous, inserted above sporangium; sclerified scales and phyllopodia occasionally surrounding microphylls. Megasporophylls and microsporophylls usually borne in alternating cycles. Megasporangia often at adaxial side of external microphyll bases. Microsporangia at adaxial side of internal microphyll bases. Sporangia solitary, adaxial, embedded in basal cavity of sporophyll, ellipsoid to subglobose, 2-7(-15) mm, walls unpigmented [or brown streaked to completely brown], traversed internally by septae; velum membranous, rudimentary [or partly to completely covering adaxial surface of sporangium wall]; megasporangium containing several to hundreds of megaspores; microsporangium containing thousands of microspores. Megaspores white when dry, gray when wet [or black], globose, 300-500(-900) μm in diam., trilete with an equatorial ridge dividing proximal and distal hemispheres and 3 radial ridges converging at pole of proximal hemisphere, surfaces smooth or textured with spines, tubercles, or ridges. Microspores gray or brown en masse, ellipsoid, 15-30(-50) μm, monolete, surfaces smooth or textured with spines, granules, or tubercles. Megagametophyte achlorophyllous, endosporic, exposed when megaspore wall opens along proximal ridges; archegonia apparent as quartets of brown neck cells. Microgametophyte 9-celled, endosporic, antheridium releasing 4 multiflagellate spermatozoids. x = [10], 11.

Zhang Libing. 2004. Iseotaceae. In: Zhang Xianchun, ed., Fl. Reipubl. Popularis Sin. 6(3): 220-223.

One genus and more than 250 species: nearly worldwide on islands and all continents except Antarctica; five species (all endemic) in China.

(Authors: Zhang Libing (张丽兵); W. Carl Taylor)