The anatomy, life history and development of the Antarctic brown alga Phaeurus antarcticus (Desmarestiales, Phaeophyceae)

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Abstract
Most aspects of the anatomy, life history and development of Phaeurus antarcticus Skottsberg are typical of the Desmarestiales. Branching is opposite, and the thallus is essentially filamentous in construction. The central axial filament, which comprises cells with thin end walls, and is surrounded by a sheath of narrow filaments, resembles the trumpet hyphae of Desmarestia. The outer surface is covered with assimilatory filaments that arise from cortical cells. Meiosporangia are unusual in that they are catenate, and zoospores develop into dioecious filamentous gametophytes. Female gametophytes consist of very few, relatively large cells, while male gametophytes form more extensive growths of narrower filaments. The oogonia and antheridia are typical of the order. Eggs are released and in culture frequently remain attached to the oogonial wall. Sporophytes develop from eggs, and also rise apogamously from vegetative cells of female gametophytes. The main axis and primary laterals of sporophytes grow by means of a trichothallic meristem, but show some additional intercalary growth attributable to elongation of the axial filament. Cortication of the main axis and primary laterals is initiated by downgrowth of filaments from cells at the base of laterals.