noun

• (Chiefly in form widgeon grass) (originally) a type of seagrass growing along the coastlines of North America and Eurasia, Zostera marina (family Zosteraceae), having long, grass-like leaves; (in later use) a widespread salt-tolerant aquatic plant growing in brackish waters, Ruppia maritima (family Ruppiaceae), having thin, thread-like leaves.

  Z. marina and R. maritima are important sources of food for many species of waterfowl.