Two β-orcinol depsidone lactones, the methyl ethers of menegazziaic acid and stictic acid were isolated along with glyceryl trilinolate and usnic acid from an Usnea sp. new to Sri Lanka growing on rotting trees of Acacia decurrans. Usnic acid exhibited potent antitermite activity against a common pest of tea, Glyptotermes dilatatus, at low elevations. Keywords: Lichen, Usnea sp., Methyl ether of menegazziaic acid, Methyl ether of stictic acid, Glyceryl trilinolate, Usnic acid, Antitermite activity.