The seasonal pattern of conceptacle development and gamete maturation in Durvillaea potatorum (Durvillaeales, Phaeophyta)

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Abstract
Monthly observations were made on the annual sequence of conceptacle initiation, development, maturation, and senescence in Durvillaea potatorum using techniques of light and electron microscopy. Conceptacles are initiated by oblique divisions of meristoderm cells which, as growth proceeds, result in the formation of clusters of branching files of cells within the cortex. The intercellular wall matrix in this region breaks down, and mucilaginous material, probably fucoidan, accumulates in the central cavity of the conceptacle. Proliferation of cells from the conceptacle wall produces the branched filaments upon which antheridia or oogonia are formed. The ostiole opens prior to maturation of the gametes. D. potatorum releases eggs and spermatozoids from June to October after which the ostioles become blocked. The old conceptacles are invaded and ultimately filled by the ingrowth of hyphal filaments and a secreted matrix of intercellular wall material. The different modes of conceptacle development in Durvillaea (Durvillaeales) and the Fucales are compared, and it is concluded that ordinal status for the Durvillaeales is justified.