Globally, subalpine and alpine plant communities are receiving increasing attention owing to disproportionately rapid warming at high altitudes, and the resultant habitat shrinkage leaving high-altitude specialists with nowhere to migrate. The Hawaiian subalpine zone (1,700–3,000 m) is an interesting example of this potential phenomenon because of the high endemism. We analyzed plant species richness, cover, and density from 89 plots (1,000 m²) sampled in 2010–2018 across two volcanic mountains, Haleakalā on Maui, and Mauna Loa on Hawai‘i. Most of the 139 plant species recorded were non-native (55%), with the remainder endemic (31%) and indigenous (14%). Plot-level richness differed from gamma diversity, with endemic species more abundant than non-native species. Non-native species richness was higher on Haleakalā than Mauna Loa. These communities are patchy with low-lying (<1 m) vegetation, and lower cover on younger drier Mauna Loa (36%) than Haleakalā (54%). Density was largely consistent with the understory cover data, with endemic Vaccinium reticulatum (>3,500/ha) and indigenous Leptecophylla tameiameiae (>2,430/ha) shrubs dominant on both volcanoes. Woodland communities were encountered only on Mauna Loa, with endemic trees Metrosideros polymorpha on wetter, south aspects, and Sophora chrysophylla on the drier, leeward side. Hawaiian subalpine vegetation varies among islands, volcanoes, and aspects, yet remains largely native-dominated, though with increasing threats from climate change, invasive non-native species, and wildfire. We recommend continued monitoring of biotic communities and climate in this sensitive zone, in situ physiological studies for the native matrix species, stricter non-native species biosecurity and sanitation protocols, wildfire prevention, and improved documentation of the effects of feral ungulates.