A new Ruppia from Mexico: Ruppia mexicana n.sp.

•We describe a new species Ruppia mexicana n.sp. found in Yucatan Peninsula, Mexico.•This species is morphologically distinct from other Ruppia species, and shares morphological characteristics with both R. maritima and R. cirrhosa from Europe.•The karyotype of R. mexicana n.sp. resembles to that of R. cirrhosa.

A study on the features of Ruppia from different sheltered bays and lagoons with marine or brackish water along the Mexican Yucatan peninsula indicates that these plants are morphologically distinct from the European Ruppia maritima. The Ruppia sp. from Mexico presents a more robust morphology, a coiled instead of straight peduncle, a slightly obliquely ovoid fruit instead of a pronounced asymmetrical one, and a chromosome number of 2n = 40 instead of 2n = 20. It is distinguished from the European Ruppia cirrhosa by its acute leaf tip. The diagnosis of Ruppia mexicana n. sp. is presented, together with data on its distribution in Mexico and some notes on other areas in Mexico where the species was found.