This is a genuinely interesting grass. No really. It is the primogenitor of saltmarsh succession, invariably the only plant to grow until it has trapped sufficient sediment to raise the land out of the tidal range inhospitable to the rest. Here it has formed a small patch of saltmarsh in Swansea Bay and was the only thing growing apart from seaweed.
It is also the best understood example of allopolyploidy: the creation of a new, fertile species from the hybridization of two species followed by chromosome doubling. Common cord-grass, Spartina anglica, has evolved from the sterile hybrid Townsend's cord-grass, S. xtownsendii. This is a hybrid of Small cord-grass, S. maritima, and Smooth cord-grass, S. alterniflora. So you get a lot of cord-grass for your buck with this tough little critter.
Smooth cord-grass was introduced from North America and the hybrid arose around Southampton in the mid nineteenth century. S. anglica was first noticed in 1892 and its vigour and sediment-trapping ability was soon recognised. Consequently it was widely planted around the coast as part of sea-defences and land-reclamation. It can grow seaward of every other perennial plant!