Ultrastructural studies on Orbilia luteorubella (Discomycetes)

Abstract

Transmission electron microscopic observations made on the ascus tip of Orbilia luteorubella showed that it is truncate and that the outer ascus wall is relatively thicker at the shoulders than on the top or sides. There is no demonstrable discharge mechanism in the ascal apex of this fungus comparable with that found in the ascus tip of other supposedly related inoperculate Discomycetes, including Mollisia cinerea.Ascospores of O. luteorubella contain a single, electron-opaque spore body that appears to evolve from a mitochondrion that is attached, at one end, to the inner wall of the spore apiculus. The function of the spore body is unknown.A blue-green alga, probably of the genus Anacystis, is associated with this and at least one other Orbilia species. Since these Orbilia species are here shown to be lichenized and they do not have an ascal pore discharge mechanism, the transfer of these fungi from the Helotiales is proposed. They can probably best be treated as lichens of uncertain affinities, perhaps related to those members of Lecanorales with iodine-negative asci.