In the study of pteridophytes, the discovery of sexual plants is generally unusual. This is due in part to the small size of the gametophytes and in part to their commonly concealed habit. In the Lycopodiaceae alone, only 10% of the nearly 500 species have known gametophytes (Bierhorst, 1971). Discovering prothallia of pteridophytes under natural conditions is one of the most challenging problems of field botany. In this paper I wish to report the first record of Lycopodium inundatum L. gametophytes for North America and to discuss their characteristics and the circumstances of their discovery. The gametophytes of the Lycopodiaceae have interested botanists for almost a hundred years since the first discovery of naturally occurring gametophytes (Fankhouser, 1873). Our understanding of these plants, however, has been greatly hindered by the rarity of collections. The most important contributions to our knowledge were all carried out well over 50 years ago by only a few notable workers. They established the taxonomic distribution of the types of gametophytes and also the major stages in the development of the gametophyte and embryo. Treub (1884; 1886a,b; 1888a,b; 1890a,b,c) in Java described the gametophyte and embryo of L. cernuum L. and several other tropical species. Goebel (1887) found and described the gametophyte of L. inundatum L. in Europe. This is the only time the gametophyte of this species has ever been reported, as far as I have been able to determine. Probably the best known work on the prothalli of the Lycopodiaceae is that of Bruchmann, who essentially laid the foundations for the systematic study of these plants. It was he who first described (1885, 1898, 1908, 1910) in detail the gametophytes of the temperate species L. annotinum L., L. clavatum L., L. complanatunm L. (which may actually have been L. tristachyum Pursh according to Wilce, 1965), and L. selago L. Bruchmann also succeeded in growing the prothalli of L. annotinumi, L. clavatlilul, and L. selago from spores, which required in some cases 6-7 years to germinate and 12-15 years to mature. An excellent review of the early attempts to germinate the spores of Lycopodiunl species was made by Chamberlain (1917). Freeberg and Wetmore (1958), in their study of the culture of Lycopodiunm gametophytes in vitro, have summarized in greater detail than is done here the contributions of Bruchmann, Treub, and Goebel.