A re-evaluation of the crustose red algal genus Cruoria and the family Cruoriaceae

Abstract

The crustose red algal genus Cruoria (Cruoriaceae) has been the subject of considerable confusion in the past, due to conflicting reports on its reproductive morphology. At times, it has been considered to consist of entities that are merely life history phases of other genera of foliose algae and thus taxonomically superfluous. Cruoria pellita (Lyngbye) Fries (the type species) and C. cruoriaeformis (Crouan & Crouan) Denizot have isomorphic tetrasporophytes and gametophytes; the latter are monoecious and bear carposporophytes. The former species is widely distributed in the north-eastern Atlantic on bedrock and cobbles, whereas the latter is more or less restricted to subtidal maerl (loose-lying coralline algae) beds in the south-western British Isles and northern France, and possibly the Mediterranean. The vegetative and reproductive morphology of both species is similar, although all structures are larger in C. pellita. It is concluded that the Cruoriaceae should be maintained as a monotypic family, characterized by: a crustose habit; a simple vegetative anatomy lacking any rhizoidal development; an absence of secondary pit connections or cell fusions; the connecting filaments originating directly from the carpogonium without formation of fusions; undifferentiated auxiliary cells; development of the gonimoblast both inwardly and outwardly from the connecting filament with very little development of sterile tissue in the carposporophyte; laterally-borne, regularly zonate tetrasporangia. Cruoria-like crusts with refractive cells, such as C. rosea (Crouan & Crouan) Crouan & Crouan and C. arctica Schmitz in Rosenvinge, have fundamentally different morphologies. They represent the tetrasporophytes of algae with heteromorphic life histories and belong to families unrelated to the Cruoriaceae.