Thallus reconstruction of nongeniculate coralline algae (Corallinales, Rhodophyta)

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Reconstruction of nongeniculate coralline algal thalli was investigated. Horizontal and vertical scars were artificially given on the branch tips of Lithophyllum pallescens growing as up to boulder-sized nodules in Kabira Cove, Ishigaki-jima, Ryukyu Islands. Time-series observations on the course of the recovery of scars have revealed followings.(1) When the horizontal scars were given, in most cases, those cells located several-cell-layrs beneath the broken cells became meristem cells that produced new epithallial cells outwardly and vegetative cells inwardly. Then the dead cells above the new epithallial cells were sloughed off. Rarely new tissues were generated from undamaged parts encircling the scars ; the scars were recovered by subsequent lateral growths of the new tissues.(2) In the case of the reconstruction of vertical scars, new cells were formed at the edges, sides, and bottoms of scars. Newly-formed tissues are dimerous at the edges and sides, while those at the bottoms are monomerous or dimerous.These results demonstrate that coralline algal thalli possess excellent capability of recovering scars by herbivores and that epithallial cells play positive role for sloughing off dead parts of coralline algal thallus, although they have been regarded as those cells terminating filaments or having a function for removing harmful objects such as other algal spores by sloughing.