In Tablet, David Mikics quotes Wallace Stevens and explains:
His grief is that his mother should feed on him, himself and what he saw,
In that distant chamber, a bearded queen, wicked in her dead light.[…] Madame la Fleurie, the flowering earth, is the “bearded queen” wickedly chomping the poet (the beard is evidently grass, a morbid riffing on Whitman’s favorite image).
In Tok Pisin, according to this online dictionary, “beard” is either mausgras (< mouth + grass) or gras bilong fes (< grass + belong + face). More generally, gras can refer to grass (including seaweeds and hay), hair, wool, or feathers. Once you’ve found it out, it seems a natural grouping.