Rossodinae, a subfamily characteristic of the pristine Malagasy rainforests (Trichoptera, Philopotamidae).The Rossodinae Özdikmen & Darilmaz, 2008, one of the three sub-families of Philopotamidae Stephens, 1829 are only known by two type specimens from the Tsaratanana Mountain, from which this subfamily has been described. An inventory of the Malagasy aquatic fauna has resulted in the discovery of a more abundant material that includes 15 species, all new and described here: Rossodes mantadia n. sp., R. pilakai n. sp., R. hertui n. sp., R. goodmani n. sp., R. manantenina n. sp., R. fabienneae n. sp., R. andohahela n. sp., R. ambreensis n. sp., R. namorona n. sp., R. marojejyiensis, R. langrandi n. sp., R. humberti n. sp., R. rakotonirinai n. sp., R. ambatomisana n. sp. and R. ankaratra n. sp. The morphological study confirmed the monophyly and the antiquity of the lineage. One of the plesiomorphic characters, the furca 4 of the male hindwings, has not been observed among the new species and exist only in the species originating from the Tsaratanana. The deformation of the inferior appendages, a remarkable apomorphy, is present in the whole lineage. Characters of male genitalia distinguish the different species, particularly the tenth tergite, the superior appendages and the internal sclerites of the phallic apparatus. The genus occurs from North to South of the island, from sea level up to 1800 m. It is strictly confined to small creeks in humid pristine forests. Its distribution is limited to the eastern slope and some of the last forests in the Central Highlands. This group illustrates the decisive effect of the vegetation on the physical and chemical conditions of running waters and, as a consequence, on aquatic wildlife. The specific distributions are small, generally limited to a single watershed.