Life history and morphology ofChondrus nipponicus(Gigartinales, Rhodophyta) from Japan

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Abstract
The vegetative and reproductive morphology of Chondrus nipponicus from Japan is described. This species is dichotomously or irregularly branched with marginal and surface proliferations. Plants are dioecious; spermatangia develop singly or in pairs from outer cortical cells; the carpogonial branches are three-celled and borne on a large supporting cell. An enveloping tissue is absent in the mature cystocarp. Tetrasporangia are transformed from intercalary or terminal branches produced secondarily from medullary cells. In culture, tetraspores from plants collected in Oshoro Bay, Hokkaido, and Iwamuro, Niigita Prefecture, gave rise to dioecious male and female gametophytes, but only under short-day conditions at 15°C. In the presence of male plants, female plants formed carposporophytes that released carpospores, which germinated in turn to form tetrasporangial plants under both long- and short-day conditions at 15°C. The species thus has a Polysiphonia-type life history. Gametangial formation is under short-day photoperiodic control, whereas tetrasporangial production is not, an unusual situation in the algae. In Japan, C. nipponicus is distributed mainly on the Sea of Japan coasts of Honshu and Hokkaido and on the Pacific coasts of northern Honshu and southern Hokkaido. Crossability studies indicate that Japanese populations of this species are entirely sexually compatible. Atlantic C. crispus is, however, not interfertile with Japanese C. nipponicus. Retention of C. nipponicus in the genus Chondrus is recommended for the time being.