Data from the summit region (3530-4400 m) of Mount Wilhelm at 5⚬ 47'S in New Guinea, although exiguous, allow the tentative recognition of four vegetation types associated with more-or-less well-defined topographic situations: (a) Ranunculus basilobatus-Deschampsia klossii forb-rich grassland of swamps and wet gentle valley slopes below about 4000 m. (b) Hierochloe redolens-cf. Poa nivicola tussock grassland of steep, well-drained slopes below about 3800 m. (c) Deyeuxia brassii-Danthonia vestita-Styphelia suaveolens herb and shrub mixtures, relatively unhomogeneous in both flora and structure, of unstable slopes, screes and boulder fields between about 3900 and 4380 m. (d) Ranunculus sarawagedicus-Tetramolopium sp. forb and low shrub mixture on actively soliflucting soils between about 4380 m and the summit (4510 m). Floristic and structural stability of the vegetation are related to the degree of system in the topography and the geomorphic processes currently going on. Tussock grassland probably replaced forest and tall shrubbery as a result of human activity. Above-ground standing crops are fairly characteristic of the vegetation type to which they belong and all are considerably greater than those of analogous vegetation types in higher latitudes.