Answer by taking a quote from the following article:

Asa Gray (November 18, 1810 - January 30, 1888) is considered the most important American botanist of the 19th century. His Darwiniana was considered an important explanation of how religion and science were not necessarily mutually exclusive. Gray was adamant that a genetic connection must exist between all members of a species. He was also strongly opposed to the ideas of hybridization within one generation and special creation in the sense of its not allowing for evolution, as he felt evolution was guided by a Creator.

Despite no longer having the burden of his professorial and garden duties, by the late 1870s the burden of maintaining himself as the pillar of American botany prevented Gray from the progress he desired on Synoptical Flora of North America, the follow-on to Flora of North America. This burden consisted of the fact that other scientists often only accepted Gray's word on a botanical matter, and the number of incoming specimens to identify was increasing vastly: numbers had to be assigned to them, collectors needed to be corresponded with, and preliminary papers had to be published. By the early 1880s, Gray's home was the center of everything to do with botany in America. Every aspiring botanist came to see him, even if just to look at him through his window.  After turning over his non-research duties to Sargent, Goodale, Farlow, and Watson, Gray concentrated more on research and writing, especially on plant taxonomy, as well as lecturing around the country, largely promoting Darwinian ideas. Many of his lectures during this time were given at the Yale Divinity School. Liberty Hyde Bailey worked as Gray's herbarium assistant for two years during 1883-1884.  In spring 1887 Gray and his wife made their last trip to Europe, this one for six months from April-October, primarily to see Hooker.  Gray received the following advanced degrees: honorary degree of Master of Arts (1844) and Doctor of Laws (1875) from Harvard, and Doctor of Laws from Hamilton College (New York) (1860), McGill University (1884), and the University of Michigan (1887).

Where else did he teach?
Gray received the following advanced degrees: honorary degree of Master of Arts (1844) and Doctor of Laws (1875) from Harvard,