 According to a 1999 study by American Society for Horticultural Science, the Ozark chinkapin, which is typically considered either a distinct species ("C. ozarkensis") or a subspecies of the Allegheny chinkapin ("C. pumila ozarkensis") may be ancestral to both the American chestnut and the Allegheny chinkapin.The leaves, which are long and broad, also tend to average slightly shorter and broader than those of the sweet chestnut.The blight-resistant Chinese chestnut is now the most commonly planted chestnut species in the US, while the European chestnut is the source of commercial nuts in recent decades.