Pennsylvania–M’Mahon came from Ireland in 1796 and began to
collect and export seeds of native American plants in 1800. His
catalog of 1804 listed seeds of about 1,000 species. In 1806, he
published his book American Gardener’s Calendar, that was for 50
years the standard gardening authority in America. There were
eleven editions of his book by the last edition published in
1857. A general catalog of garden plants was published at the
end of the book. He knew Jefferson and his store became the
meeting place of botanists and horticulturists. M’Mahon helped
to distribute the seeds collected by the Lewis and Clark
Expedition. M’Mahon died on September 16, 1816. Sources: Plants;
Woodburn2; CHSJ-Apr. 1966; Leighton1;