"[4] Ann Leighton notes the absence of Indian corn among the "Seeds of Esculent Vegetables" in 1806, though he lists old-fashioned favorites like coriander, corn-salad, orach, rampion, rocambole and skirret.
[6] In 1808 McMahon purchased twenty acres on the Germantown Road, in Penn Township, Philadelphia for a nursery and botanic garden that would enable him to expand his business.
In 1818 botanist Thomas Nuttall honored McMahon by bestowing the genus name Mahonia on a group of West Coast broadleaf-evergreen shrubs still popular in American gardens.
McMahon, growing the seedlings that were protected from commerce as Federal property, had the mortification to see published in British journals, and to see Mahonia nervosa itself introduced by Prince Nurseries, Flushing, Long Island, at twenty dollars a plant.
[11] At his death the nursery business was left to his wife, Ann McMahon (d. 1818),[10] and their son, Thomas P. M'Mahon, who continued to revise and republish The American Gardener's Calendar.