Crop wild relatives are important genetic resources for cultivar improvement. Domesticated apple (M. x domestica) cultivars grown in North America are heterogeneous hybrids of Asian and European Malus species, with no known genetic contribution from native apples. M. coronaria (Sweet Crabapple) is the only native apple species found within the major apple-producing Great Lakes region. In spite of its potential importance for apple cultivar improvement, the genetics of this species has not been well studied, and only a few accessions are maintained in the USDA National Plant Germplasm System (NPGS). The objective of this research was to identify and collect new accessions of M. coronaria for the NPGS, focusing on the northernmost extent of its range in Michigan. To locate living trees, we combined analyses of historical records in 12 herbaria and the North America Fruit and Nut Tree Data, along with crowdsourcing using the popular online platform, iNaturalist. We identified a total of 158 M. coronaria records from herbaria and the fruit tree dataset. Records were removed from consideration if they were cataloged earlier than 1950, did not include collection coordinates, were redundant, or were not collected in the state of Michigan. iNaturalist listed 309 sightings of M. coronaria in Michigan; of these, we determined that a majority were likely misidentified based on the phenotypic characteristics in the images provided by the observer. Finally, Google Earth was used to rule out locations where the M. coronaria individuals had likely been lost due to anthropogenic activity. Ultimately, this three-factored approach identified only 64 sites within the state of Michigan where a living tree would likely be found. Our results provide strong evidence that M. coronaria is in decline within its native range in Michigan, underscoring the importance of conservation efforts for this species.
