First Report of Polysiphonia morrowii Harvey (Ceramiales, Rhodophyta) in the Mediterranean Sea

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Abstract
Polysiphonia morrowiiHarvey (Rhodophyta), native to Japan, Korea, China and Russia, is here reported for the first time from the Mediterranean Sea. Thalli were first found in 1999 off the Island of Chioggia, where imported clams and fish are handled; the following year, plants were also found near the Island of Venice itself. Polysiphonia morrowii is similar to Polysiphonia senticulosa Harvey, as reported from Japan and the north Pacific, and to Polysiphonia stricta (Dillwyn) Greville [= Polysiphonia urceolata (Dillwyn) Greville] from the Mediterranean basin. The specimens collected in the Lagoon of Venice are characterised by two of the most significant specific features of P.morrowii: endogenous axillary branchlets forming from the central axial cells, and tufts of axillary tetrasporangial branchlets on the axils of mature plants. The morphology and reproduction of P. morrowii are examined on the basis of the material collected at Venice.