Any of several plants, such as knotgrass, producing numerous seeds.
The forest is thick with trees-- beech( SS13), oak( SS15, CS15, OP28), pine( OP30), sycamore( CS15), and yew( OP21) are mentioned, as well as undergrowth such as knotgrass and thorns( OP30)-- but there are paths, brooks, and some clearings.