Prior to 1840, besides what he had discovered during his trip to Europe, Gray's knowledge of the flora of the American West was limited to what he could learn from Edwin James, who had been on the expedition to the West of Major Stephen Harriman Long, and from Thomas Nuttall, who had been on an expedition to the Pacific coast with Nathaniel Jarvis Wyeth. In the latter half of 1840, Gray met the German-American botanist and physician George Engelmann in New York City. Engelmann took frequent trips to explore the American West and northern Mexico. The two remained close friends and botanical collaborators. Engelmann would send specimens to Gray, who would classify them and act as a sales agent. Their collaborations greatly enhanced botanical knowledge of those areas. Another German-American botanist, Ferdinand Lindheimer, collaborated with both Engelmann and Gray, focusing on collecting plants in Texas, hoping to find specimens with "no Latin names". Another long-term and productive collaboration was with Charles Wright, who collected in Texas and New Mexico on two separate expeditions in 1849 and 1851–1852. These trips resulted in publication of the two-volume "Plantae Wrightianae" in 1852–1853.