Nelson circa 1909
|Born||24 March 1859|
Lee County, Iowa
|Died||31 March 1952 (aged 93)|
Colorado Springs, Colorado
|Alma mater||University of Denver|
|Known for||President, University of Wyoming|
|Spouse(s)||Celia Alice Calhoun (1860-1929)|
Ruth E. Ashton (1896-1987)
|Institutions||University of Wyoming|
Aven Nelson (March 24, 1859 – March 31, 1952) was an American botanist who specialized in plants of the Rocky Mountains. He was one of the founding professors of the University of Wyoming, where he taught for 55 years as professor and served as president (1918-1922). He served as president of the American Society of Plant Taxonomists and Botanical Society of America.
Nelson was born at Sugar Creek, in Lee County, Iowa to parents Christen Nelson and Anne (Evenson) Nelson, who had immigrated from Norway. Aven was the youngest of four children in a Quaker family. He attended Kirksville State Normal School in Kirksville, Missouri from which he was graduated in 1883 with his Bachelor of Arts degree, while in 1887 he received the M. S. D. degree. He further continued his education in Drury College at Springfield, Missouri, which conferred upon him a Master of Science degree in 1890. He next entered Harvard University was awarded the Master of Arts degree in 1892. In 1893, he co-founded the Rocky Mountain Herbarium.  
He came to the University of Wyoming in 1887. In 1901, he was made fellow of the American Association for the Advancement of Science. In 1904, the University of Denver conferred upon him the degree of Doctor of Philosophy. In 1917, Nelson was named acting president, then president (1918) of the University of Wyoming, a position he held until 1922. In 1934, he was elected president of the Botanical Society of America. In 1927, he co-founded the Colorado-Wyoming Academy of Science. In 1935, he became president of the American Society of Plant Taxonomists. 
In 1885, he married Celia Alice Calhoun (1860-1929). They were the parents of two children. In 1931, he married Ruth Elizabeth Ashton (1896-1987) in Santa Fe, New Mexico. He died in Colorado Springs, Colorado in 1952. The Aven Nelson Memorial Building on the campus of the University of Wyoming is named in his honor.
- First report on the flora of Wyoming (1896)
- The Trees of Wyoming and How to Know Them (1899)
- The Red Desert of Wyoming and its forage resources (1898)
- The Flora of Montana (1900)
- The Cryptogams of Wyoming. A Preliminary Report upon those Species (1900)
- The Brome-Grasses of Wyoming (1901)
- An Analytical Key to Some of the Common Flowering Plants of the Rocky Mountain Region (1902)
- Spring Flora of the Intermountain States (1912)
- "Aven Nelson, Biographical and Professional Information". American Heritage Center at the University of Wyoming. Archived from the original on 2016-01-27. Retrieved January 5, 2016.
- "Aven Nelson, Founding Member of UW, Botanist,". storify.com. Archived from the original on 2016-01-27. Retrieved January 5, 2016.
- "Aven Nelson, UW Professor & President". University of Wyoming. Retrieved January 5, 2016.
- "About the Rocky Mountain Herbarium". University of Wyoming. Archived from the original on March 4, 2016. Retrieved January 5, 2016.
- Bartlett, Ichabod Sargent (1918). "Professor Aven Nelson". History of Wyoming. S. J. Clarke Publishing Company. pp. 588–589.
- Charlotte Goodding Reeder (1969). "Chronology of the life of Dr. Aven Nelson". University of Wyoming. Archived from the original on January 26, 2016. Retrieved January 5, 2016.
- "About The Colorado-Wyoming Academy of Science". Colorado Wyoming Academy of Science. Retrieved January 5, 2016.
- "Aven Nelson Building". University of Wyoming. Retrieved January 5, 2016.
- IPNI. A.Nelson.
- Knobloch, Frieda E. (2005) Botanical Companions: a Memoir of Plants and Place (University of Iowa Press) ISBN 9781587294525
- Williams, Roger L. (1984). Aven Nelson of Wyoming. (Colorado Associated University Press). ISBN 0870811479.
- This article incorporates text from a publication now in the public domain: Bartlett, Ichabod Sargent (1918). "Professor Aven Nelson". History of Wyoming. (S. J. Clarke Publishing Company). pp. 588–589.