Review of a herbarium specimen (QBG) and subsequent field studies have revealed that Diphasiastrum multispicatum occurs near the summit of the two highest mountains in Thailand. This species is restricted to SE Asia and grows exclusively at higher elevations in the submontane to montane zone. Previously, it has been reported from China, the Philippines, Taiwan, and Vietnam, but not from Thailand. A comparison of the plants from Thailand with those from the type locality of D. multispicatum in the Philippines (Mt. Santo Thomas near Baguio City, Province of Benguet, Luzon), where this species is still present, shows the plants from Thailand to be D. multispicatum. Like other Diphasiastrum species, D. multispicatum is a weak competitor and grows on (disturbed) immature soils on slopes with more or less open and low growing vegetation. We also present morphological evidence that Diphasiastrum multispicatum is distinct from Diphasiastrum complanatum s.s., which is a north temperate, circumboreal species (in northern and central Europe, Greenland, northern North America, Japan and northern Asia, excluding the tropics).