This genus has heavily diversified into many species throughout islands across the tropical Pacific.

The most enigmatic species of the genus, the large-billed reed warbler (A. orinus), was rediscovered in Thailand in March, 2006; it was found also in a remote corner of Afghanistan in the summer of 2009.

[2][3] The type species was designated as Turdus arundinaceus Linnaeus, 1758, by the English zoologist George Gray in 1840.

[6] The genus contains 42 species of which 6 insular forms are now extinct:[7] Fragmentary fossil remains from the Late Miocene (about 11 mya) of Rudabánya (NE Hungary) show some apomorphies typical of this genus.

[8] Given its rather early age (most Passerida genera are not known until the Pliocene), it is not too certain that it is correctly placed here, but it is highly likely to belong to the Acrocephalidae at the least.