Origin, status and ecology of the hybrid Marram Grass in Britain

The cytology and population ecology of a naturally occurring intergeneric hybrid, x Calammophila baltica, the hybrid marram grass, was investigated in terms of its genome inheritance from, and ecological interactions with its progenitor species, Ammophila arenaria (marram grass) and Calamagrostis epigejos (bush grass). Cytological studies confirmed that the hybrid was probably the reported combination of genomes, and a possible karyotype is described. Studies on meiosis showed this process to be very disturbed in the hybrid, and slightly disturbed in A. arenaria. Pollen stainability (= fertility) tests suggested that the hybrid is capable of producing very low amounts of viable pollen. The hybrid was found to be generally limited to sand dunes and only on the East Anglian coast and at Ross Links, in Northumberland. In E. Anglia it was also found behind the dune system, in an atypical marram habitat. Morphometric studies showed x C. baltica to be intermediate between its progenitors for most of the characters measured. Multivariate analyses of these characters suggest that there were only two successful hybridisation events in Britain. Studies of the rhizomes branching patterns showed that the `plant shape' of the hybrid was completely different from that of A. arenaria, and that it is this, plus the rhizome structure, which enables these two species to avoid competition. Multivariate analysis of quadrat data showed that the two species responded differently to their environment and a series of competition experiments, under controlled conditions, showed that their coexistence could be mutually beneficial. Growth rates and the allocation of biomass dry weight and water within the plant varied in different ways between the three species, according to environmental conditions and age. It was concluded that there was no problem of niche overlap between the hybrid and marram, due at least in part, to the influence of the C. epigejos genome. Finally a conceptual model, encompassing the factors affecting the development, growth and survival of hybrid genets is presented. (D74418/87)