Chloroplast DNA variation in Dactylis glomerata L-taxa endemic to the Macaronesian islands

In the Dactylis glomerata infraspecific polyploid grass complex, restrictio n fragment length polymorphisms (RFLPs) of chloroplast DNA (cpDNA) were stu died in diploid and tetraploid populations of several taxa endemic to Macar onesia (Madeira and the Canary islands) and in populations from the African and European continental areas closest to Macaronesia. Two chlorotypes, wh ich differed by a single 290-bp length mutation, were observed in the Macar onesian and the continental populations. Chlorotype I,which is predominant in the whole D. glomerata complex, was found in the majority of continental populations. It was also observed in the most western Macaronesian islands , in the two diploid taxa endemic to the lowland scrub and the high elevati on heath of Tenerife, respectively, and in tetraploids endemic to Madeira a nd La Palma. These island populations were growing under the influence of h umid trade winds. Chlorotype II was found in the eastern part of the Archip elago (closer to Africa), which experienced subarid Mediterranean climate c onditions, and in very few diploid and tetraploid Mediterranean populations growing at high elevation on the continent. This geographical and climatic distribution of chlorotype variation in Macaronesia is consistent with tha t reported previously for morphological, allozyme and phenolic variation in the same plant material. Chlorotype II was, however, also observed in tetr aploid populations from La Gomera island and in one of the seven tetraploid populations analysed from Madeira, which all showed clearly subtropical ch aracters for morphology, allozymes and phenolic compounds. This result sugg ests that cpDNA introgression has occurred more than once from the Mediterr anean material into the subtropical one and may indicate that colonization between the mainland and islands, or among the islands, probably played a m ajor role in the geographical pattern observed for that marker.