The late pre-contact vegetation of Hālawa Valley, Moloka‘i Island, is assessed through the analysis of macroscopic (charcoal) and microscopic (pollen, phytoliths, and starch grains) plant remains recovered from archaeological excavations of sites dating to the period from 1600 to 1800 C.E. The results indicate an anthropogenically modified, open landscape dominated by Polynesian-introduced cultigens (“canoe plants”), ferns, sedges, and grasses, and a limited number of indigenous or endemic shrubs or trees with known uses in traditional Hawaiian culture. Nine Polynesian introductions are represented in the archaeobotanical record, including trees (candlenut, breadfruit, coconut, and Malay apple) and field crops (taro, banana, ti, noni, and bottle gourd). Sampling of the contemporary vegetation of Hālawa Valley at 238 locations demonstrates the persistence of these and several other Polynesian-introduced taxa, whose populations may preserve cultivars of ethnobotanical significance.