MORPHOLOGY AND SYSTEMATICS OF THE RED ALGAL PARASITE DAWSONIOCOLAX-BOSTRYCHIAE (CHOREOCOLACACEAE, RHODOPHYTA)

The vegetative and reproductive development of the parasitic red alga Dawsoniocolax bostrychiae (Joly et Yamaguishi-Tomita) Joly et Yamaguis hi-Tomita, a parasite on Bostrychia, was studied. The thallus is a col ourless multiaxial pustule which forms secondary pit connections with cells of its host. Reproductive structures develop from outer cortical cells. Tetrasporangia are tetrahedrally or cruciately cleaved. A four -celled carpogonial branch is borne on an intercalary supporting cell, which also functions as the generative auxiliary cell. After fertiliz ation, the carpogonium fuses with the supporting (auxiliary) cell. The mature carposporophyte consists of a central fusion cell supporting a hemispherical cluster of gonimoblast filaments bearing terminal carpo sporangia. Carposporophyte development is similar to Harveyella mirabi lis (Reinsch) Schmitz et Reinke and Leachiella pacifica Kugrens. Sperm atangia develop in globose clusters formed by divisions in several pla nes of the spermatangial initials. This information supports placement of Dawsoniocolax in the family Choreocolacaceae (together with Choreo colax, Harveyella and Leachiella) which is retained in the Gigartinale s.