Rostraria grass on London brownfield site

Rostraria grass on London brownfield site

Observation - Rostraria grass on London brownfield site - UK and Ireland. Description: Can't find this in Rose and failed to key it out to a sensible answer in Stace III (though I'm very rusty on grasses and may just have gone wrong). Help needed!

Can't find this in Rose and failed to key it out to a sensible answer in Stace III (though I'm very rusty on grasses and may just have gone wrong). Help needed!