Primeroles

An old name used for various types of early-flowering plants (the name gave rise to later 'primrose', though it is used in a more general sense in the quotation above). They were found by Frodo and Sam growing among the many plants and flowers of Ithilien. It's implied that they could also be found elsewhere in Middle-earth (for example, Frodo's mother Primula took her name - or at least its anglicised version - from another term for this group of flowers).

Incidentally, the 'filbert-brakes' mentioned in the quotation above are also derived from an old plant name; in this case the reference is to thickets of wild hazel.