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Dictyotales (division Phaeophyta) An order of brown seaweeds in which growth occurs from a single apical cell or an apical margin of cells. The thallus is flattened and there is an isomorphic alternation of generations. Members are common in warmer regions. Dictyota dichotoma is yellowish-brown to olive-brown, and the flattened fronds fork regularly; this species is found in intertidal regions in rock pools, and in deeper water at and below low-water mark.