This is the plant I’ve come to know as nut grass (as compared with the plants at sightings 4651501 & 4651505. The flower/seed head is all green and consists of 5 distinct clusters. (Those of the earlier quoted sightings have less clusters, and they are all white). The leaves of this plant are long, thin, and a shiny dark green, and have a distinct ‘v-shape’ profile.
The other plant they are growing amongst is the subject of sighting 4650691