Aims: The USNVC is the standard for vegetation classification in the US and is part of the broader IVC. Recent work on the USNVC in Alaska established macrogroups, groups and alliances. Here we incorporate tussock tundra and low and tall willow (Salix) groups and alliances for northwestern Arctic Alaska into the IVC and USNVC classification. Study Area: The study area encompasses the Seward Peninsula, the western Brooks Range, and the northwestern foothills and Arctic coastal plain of Alaska. Methods: We used data from 2,087 relevé plots collected between 1992 and 2019 from northwestern Arctic Alaska to prepare a draft association classification using cluster analysis, ordination, and sorted tables. The draft classification was subject to peer review and subsequently refined. We fit the tussock tundra and low and tall willow associations into the USNVC using NMDS and GAMs to evaluate the patterns of environmental gradients against the ordination axis scores. Results: We identified eight tussock tundra and 37 low and tall willow associations. The associations fit in two classes, two subclasses, two formations, two divisions, three macrogroups, four groups, and 13 alliances. A description of the alliances, and a field guide to the northwestern Arctic Alaska tussock tundra and low and tall willow associations, including a dichotomous key and descriptions, is provided. Conclusions: Many of the tussock tundra and low and tall willow associations fit seamlessly within the USNVC, while some alliances had yet to be defined, and we have proposed new alliances here. In still other cases, we proposed a new group and recommend broadening the concept of an existing group using a data-driven approach. Since not all available data from Arctic Alaska were used in this study, we suggest continuing with a more comprehensive analysis to fulfill the gap at the alliance and association levels for Arctic Alaska.<br> Taxonomic reference: USDA NRCS (2021) for vascular plants, bryophytes, and lichens.<br> Syntaxonomic reference: USNVC (2019).<br> Abbreviations: AVA-AK = Alaska Arctic Vegetation Archive; AVPD = Alaska Vegetation Plots Database; BCP = Beaufort Coastal Plain; CAVM = Circumpolar Arctic Vegetation Map; CBVM = Circumboreal vegetation map; EC = Electrical conductivity; ELD = ELS Legacy Database; ELS = Ecological Land Survey; GAM = Generalized additive model; IVC = International vegetation classification; LPI = line-point intercept; NMDS = Non-metric multidimensional scaling; PAM = Partitioning Around Medoids; PESC = Proportionate ericaceous shrub cover; SM = Supplementary material; US = United States of America; USNVC = U.S. National Vegetation Classification.
