Abstract
Field observations showed that in its native Texas grasslands, dodder (Cuscuta attenuata) grows more vigorously in patches of mixed host species than in monospecific host patches. Field experiments with naturally occurring host individuals demonstrated that the parasite achieved greater volume when simultaneously infesting two hosts of differing species rather than two hosts of the same species, and that this effect depends on the order in which the parasite encounters those hosts. Sodium, acting as an osmoticum, is implicated as the factor responsible for experimentally produced as well as observed field patterns.