Morphology and phylogenetic systematics ofPtilocladiopsis horridaand proposal of the Ptilocladiopsidaceaefam. nov. (Gigartinales, Rhodophyta)

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Detailed morphological and molecular analyses of Ptilocladiopsis horrida have resulted in the proposal of the Ptilocladiopsidaceae fam. nov. Molecular analyses placed the new family in the Gigartinales in a basal position relative to families that comprised the Dumontiaceae complex. Plants were erect, monopodial, and grew by transverse division of an apical cell. Each axial cell cut off four periaxial cells that progressively elongated and distally bore branched filaments. Inner cells of the branched filaments expanded progressively toward the outside to form a three-layered cortex bearing free filaments along the surface of the thallus. With the elongation of the periaxial cells, the basal cells of the branched filaments separated from the central axis to produce a hollow space around it. Spermatangial parent cells and carpogonial branches were produced from the innermost cells of the free filaments. Carpogonial branches were four-celled and strongly reflexed, with the trichogyne directed outwardly. The fertilized carpogonium fused with the third cell of the carpogonial branch and produced up to four connecting filaments, one of which could fuse with the supporting cell, which functioned as an auxiliary cell (procarpic condition); others elongated and fused with remote auxiliary cells (nonprocarpic condition). The auxiliary cell cut off a gonimoblast initial that differentiated into a primary gonimoblast cell bearing branched gonimoblast filaments, most of which matured into carposporangia. The primary gonimoblast cell fused with the auxiliary cell, which elongated to continue growth of the connecting filament. Mature gonimoblasts protruded from the thallus surface and were surrounded by a sparsely branched filamentous involucre. Tetrasporophytes have not been observed. Previous accounts failed to show the presence of connecting filaments, leading to the placement of Ptilocladiopsis in the procarpic order Ceramiales.

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