Small, aromatic, low, the pennyroyal may be walked upon without anyone noticing that it is there, until the sweet aroma of the crushed leaves and stems fills the summer air. Pennyroyal is one of the most fragrant of the mints, with none of the acrid quality of some of the pungent or bitter members of the family. Pennyroyal tea, brewed from the dried and crumbled leaves, contains the essence of that flavor of the dry summer hills.
Hedeoma hispida Pursh.
Pennyroyal is part of the mid-summer flora of the dry oak woods floor, there on the hilly places where the soil is caked and cracked during the periods of no rain and much heat. These are the woods where the wood pewee wails thinly all day long, from three o'clock in the morning until nine o'clock at night; woods known by the fox squirrel and the big velvety cecropia moths. Woods like these may be full of early bloom, but in mid-summer there is almost nothing in bloom, and the sparse vegetation is dry and almost without life. Somehow the pennyroyal manages to bloom and live until, in late summer and early autumn, the little low plants finally grow dry and sere. It is now that their aromatic perfume is strongest in the warm days of September. Even under snow, and at the ragged end of winter, the remaining little thin stems and remnants of leaves continue to hold that unmistakable odor.
Two species of pennyroyal are found in Illinois. The American pennyroyal (Hedeoma pulegioides) is most abundant throughout woods, is most aromatic and is taller than other pennyroyals. The leaves are elliptical and petroled. Rough pennyroyal (Hedeoma hispida) has sessile, linear leaves, is very hispid, and is limited to sandy soils.