THE REPRODUCTIVE MORPHOLOGY OF PLATOMA-CYCLOCOLPUM (NEMASTOMATACEAE, GIGARTINALES) FROM GRAN-CANARIA, CANARY-ISLANDS

Nine species are currently included in the marine red algal genus Plat oma (Nemastomataceae, Rhodophyta), which is typified by P. cyclocolum (Montagne) Schmitz described by J.F.C. Montagne (as Halymenia cyclocol pa) in the early part of the last century from Tenerife, Canary Island s. Recently collected plants of Platoma cyclocolpum from another of th e Canary Islands, Gran Canaria, are similar in morphology and reproduc tion to type material of Halymenia cyclocolpa Montagne, for which a le ctotype is selected. Connecting filaments of P. cyclocolpum, arise fro m subsidiary auxiliary cells fused or connected with fertilized carpog onia in the same manner as found in Schizymenia. These specimens and M ontagne's material have large intercalary gland cells in the cortical fascicles. The other eight known species of Platoma and some other mem bers of the Nemastomataceae require reinvestigation to establish their generic and familial relationships, but it is clear that Platoma, Sch izymenia and Titanophora are more closely related to each other than t hey are to the remaining genera of the Nemastomataceae and should prob ably be referred to a separate family. The new combinations Tsengia la ncifolia (Okamura) comb. nov. (basionym: Nemastoma lancifolium Okamura ) from Japan and Tsengia pulchra (Baardseth) comb. nov. (basionym: Nem astoma pulchrum Baardseth) from Tristan da Cunha are proposed. Carposp ores of Gran Canarian P. cyclocolpum developed into coherent crustose plants without gland cells; these superficially resemble the Haematoce lis-phase of Schizymenia dubyi (Chauvin ex Duby) J. Agardh, but lack t he refractive cell inclusions and secondary pit-connections between ce lls of adjacent perithallial filaments described for this phase. The P latoma crustose phase did not form erect axes and no sporangial reprod uction took place under a wide range of environmental conditions.