The morphology of Phaeocolax kajimurai (Rhodomelaceae, Rhodophyta), a host specific epiphyte on Lobophora variegata (Phaeophyta)

Abstract

Phaeocolax kajimurai Hollenberg (Rhodophyta) displays morphologically distinct endophytic and exposed axes. After germination an endophytic prostrate base develops beneath the outer cortical cell layer of the only known host, Lobophora variegata (Lamouroux) Womersley, a brown alga. Enlargement of the prostrate base by rapid cell divisions eventually causes the outer cortical layer of the host to rupture. Emergent growth develops into corticated polysiphonous main axes. Reproductively, Phaeocolax kajimurai displays characters typical of the Rhodomelaceae (Rhodophyta). The procarp consists of a four-celled carpogonial branch with only one three-celled sterile group. A well-formed pericarp surrounds the developing carposporophyte. Cylindrical spermatangia bear a sterile cap cell. Each of the five pericentral cells in a fertile branchlet may bear a tetrasporangium. The association of Phaeocolax kajimurai with its host is one of a host specific epiphyte, and is one of the few documented cases in which a red alga lives in close association with a brown alga.