A new species from the semiaquatic weevil genus, Notiodes sporocarpicus, which develops and pupates in the sporocarps of the water fern Marsilea mollis B.L. Rob. & Fernald, is described from cattle tanks in southeastern Arizona. This new species can be separated readily from the majority of the known species by its nearly straight rostrum, with its distinctive dorsally swollen base and attenuated apex. Its elongate and slender body will separate N. sporocarpicus from most species in the genus except N. aeratus, which lacks the characters above. The Texas species N. celatus resembles the new species but has strongly developed suberect curved setae that are not present in N. sporocarpicus. Included are habitus photos and line drawings of the male and female genitalia of the new species.