WordNet sense 1 (annual having the stem beset with curved prickles; North America and Europe and Asia):

catchweed, cleavers, clivers, Galium aparine, spring cleavers

WordNet sense 2 (low-growing perennial having leaves silvery beneath; northern United States; Europe; Asia):

goose-tansy, silverweed, Potentilla anserina

WordNet sense 3 (annual weedy grass used for hay):

Panicum Texanum, river

WordNet sense 4 (coarse annual grass having fingerlike spikes of flowers; native to Old World tropics; a naturalized weed elsewhere):

yardgrass, wire grass, Eleusine indica