Linn Perennial Ryegrass Seed will be substituted with Mathlilde Tetraploid Perennial Ryegrass Seed. Call our office with any questions (800-552-1027). Linn Perennial Ryegrass seed is more persistent than annual Ryegrass Seed, but less persistent in the midwest than other cool season grass species. Perennial Ryegrass can behave as an annual, short-lived perennial, or perennial, depending on environmental conditions. It resembles annual Ryegrass (Lolium multiflorum Lam.), although perennial Ryegrass has more leaves in lower parts of the plant canopy, its collar and blade are more narrow, and lemmas are awnless.