The ultrastructure of phycobiont and mycobiont in two species of Usnea

Abstract

The ultrastructure of two closely related species of lichens, Usnea rockii Zahlbr. and U. pruinosa Mot., was examined to determine the morphology of the phycobionts, the mycobionts, and their interrelation. The ultrastructure of the two species is essentially the same. A comparison of lichenized fungi and algal cells at the ultrastructure level was made with the ultrastructure of fungal and algal cells as known from the literature. The ultrastructure of the phycobionts is similar to that of free-living algae. The mycobionts displayed structural differences in their walls which apparently are unrecorded for fungus hyphae, resulting in a striking polymorphism of the hyphae. Close contact between mycobiont and phycobiont was seen, and intramembranous haustorial penetration of the algal wall was demonstrated in Usnea rockii.