Sue Keys, my friend at the Gazette-Journal, texted me last week with a gardening question: “Is a native cultivar still a native? Am looking at ‘Sunny Boulevard’ St. John’s Wort for the GJ beds.” Besides working very hard to make sure columns like mine don’t contain too many typos or grammatical errors, another of Sue’s gigs is trying to keep the garden beds that border the newspaper building looking spiffy.

Sue is not the only person currently asking this question. I follow numerous native plant sites online, and this issue frequently arises. There is no easy answer, so the best place to start is at the beginning.

From the early colonial days, explorers introduced new and unusual species of plants from Europe, Asia, and Africa into North America. Many species of trees, shrubs, vines, and flowers thrived in the New World. Some plants reminded settlers of those grown in their gardens across the ocean. Others, like camellia, gardenia, and crape myrtle, gained popularity because the...