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CommentsThe most remarkable thing about this little plant is the strong scent of the foliage. Otherwise, it is rather easy to overlook. The only other species in this genus that occurs in Illinois, Hedeoma hispida (Rough Pennyroyal), has linear leaves and a milder scent; it also prefers sunnier habitats. American Pennyroyal superficially resembles Gratiola neglecta (Clammy Hedge Hyssop), but this latter species lacks any fragrance and its prefers soggy habitats (e.g., damp depressions in woodlands). Native pennyroyal species (Hedeoma spp.) have only 2 stamens per flower, while other similar species in the Mint family often have 4 stamens per flower. Because the flowers are so small, this requires a 10x hand lens to see clearly.