I realized I needed that poem when I was using the iNaturalist app in the swampy unmowed green by Brookside’s parking lot. Barely moving a quarter turn, I had photographed two sedges and a rush huddled together, celebrating their reprieve from Grantham’s mower and congratulating each other on their contribution to biodiversity at Brookside Park. I found a grass on a subsequent visit, easily recognized with the help of an Illinois Extension Blog that quoted the poem in full:
Sedges have edges,
Rushes are round,
Grasses have nodes from the top to the ground
https://extension.illinois.edu/blogs/grasses-glance/2023-04-17-telling-apart-grasses-sedges-rushes