Ceratopteris richardii

Plants floating or rooted. Sterile leaves lanceolate to deltate to ovate. Petiole of sterile leaf 1--11 cm, not inflated; small leaves lobed to pinnate, segments or pinnae with entire to somewhat incised margins, larger leaves 2-pinnate-pinnatifid with deeply incised pinnae. Blade of sterile leaf 3--16 × 2.5--17 cm, pinnae deltate to ovate; proximal pinnae usually alternate. Fertile leaves lanceolate to deltate to ovate to 19 × 12 cm. Petiole of fertile leaf 6--9 cm. Blade of fertile leaf 2--3-pinnate; terminal segments narrow. Sporangia scattered to densely crowded between midvein and revolute margin, with 20--40 or more indurate annulus cells. Spores 16 per sporangium, 107--150 µm diam. 2 n = 78.

Aquatic to semiaquatic; lakes and ponds; 0 m; La.; West Indies; Central America in Guatemala; South America; Africa.

According to L. G. Hickok (1977), Ceratopteris richardii is diploid. Morphologically, specimens from the United States are difficult to distinguish from tetraploid C . thalictroides . The primary characteristic distinguishing C . richardii is its 16-spored sporangia. Herbarium specimens with 16-spored sporangia from the West Indies and Latin America have variable morphology ranging from that of C . pteridoides to that of C . thalictroides (R. M. Lloyd 1974, fig. 6). Some specimens have both 16- and 32-spored sporangia. This suggests multiple origins for C . richardii . Because reproductive isolation is incomplete among the diploid taxa, and highly fertile F 2 segregates of various morphologic types occur, further work is needed to determine the nature, origin, and distinctness of C . richardii .