Nymphs of Leptobasis lucifer (Donnelly) were collected in shallow water in a cypress (Taxodium distichum (Linnaeus) Richard (Taxodiaceae)) dome in southern Florida. They differ from L. vacillans Hagen in Selys, the only Leptobasis species previously described, by ratio of length of antennomere 2 to antennomere 1 (1.6 in L. lucifer, 1.4 in L. vacillans), cercus length (0.13–0.17 mm in L. lucifer, 0.08–0.13 mm in L. vacillans), and length—width ratio of caudal lamellae (> 4.0 in L. lucifer, < 4.0 in L. vacillans). Leptobasis is most similar to Ischnura Charpentier and Enallagma Charpentier; a combination of characters, including head width and the arrangement of setal bases on the lateral carinae of the abdominal segments, is necessary to separate these genera.