Salt marshes occupy a narrow intertidal zone where conditions change from marine to terrestrial. As a consequence they exhibit severe clines in salinity and soil saturation. The characteristic zonation of the vascular plant communities occupying these habitats is believed to develop as a result of differential tolerance and competitive abilities of the plants that comprise them. There are however few data on the structure of salt marsh communities relative to either elevation or tidal inundation. The consequences of soil saturation and salinity may also affect the distributions of soil microflora, including the occurrence and development of arbuscular mycorrhizal fungi. As AM development can result in enhanced plant performance, and may alter competitive interactions, any edaphic limitation in their development could influence plant community development. Detailed surveying, and the use of two objective methods of defining zonation, has allowed a full description of the plant community structure, relative to elevation, to be made. This identifies three distinct species groupings within the zonation, and has enabled the identification of competitive dominants within the zonational sequence. The occurrence of AM development within the salt marsh community has also been accurately determined for the first time. This represents the first survey of AM fungi in UK salt marshes since 1928, and identifies a distinct cline in the occurrence of these fungi relative to inundation. The effects of mycorrhizal development by AMF isolated from salt marsh sediments on the growth of 5 halophytes is ascertained. The results suggest salt marshes are environments where the usual benefits of AM development do not apply. This may explain the low levels of mycotrophy observed amongst halophytes.