Soft/Common Rush (Juncus effusus)

Where to plant: fresh to brackish water; shallow and muddy zones (less than 6 inches). Tolerant of diverse site conditions.
Type: rush or sage (perennial)
Height x spread: 1-3 x 2-4 ft.
Blooms:  summer
Bloom: showy, yellowish-green
Sun: thrives in direct sun, tolerates partial shade
Water: wet
Maintenance: low
Tolerates: wet soil; prevents erosion

 

https://pondinformer.com/soft-rush-juncus-effusus/
https://en.wikipedia.org/wiki/Juncus_effusus