A native of Missouri, Marion Ownbey was one of three twentieth century Ownbeys associated with plant taxonomy, the others being his brother Gerald Ownbey and his wife Ruth Peck Ownbey. His botanical education began at the University of Wyoming and its Rocky Mountain Herbarium and continued at Washington University in St. Louis and the associated Missouri Botanical Garden. Major influences on the early parts of his education were Aven Nelson and J. M. Greenman, two older taxonomists whose methods stressed close study of the details of plants, especially of dried specimens, and careful and precise organization of the knowledge of those plants. Their approach had been especially useful in criticising and revising the original description of North American flora, a development in which both had also participated. Though their approach was similar to that long used by botanists, it tried the patience of many, who could see no relation between modern science and the dried plant collections of the "haymaker" botanists, as they were derisively called. Moreover, their field had been much vexed by a troublesome and perhaps needless debate over the rules of botanical nomenclature. Nevertheless, by the 1920s and 1930s American taxonomists had essentially completed a catalog of North American plants and were well into a cycle of critical revision. This revisionary cycle consisted largely of a long sequence of "monographed genera." By the 1920s, this expression had come to mean the extensive and comprehensive examination of all literature and herbarium specimens of particular genera, resulting in lengthy and exhaustive monographic publications, then considered the mark of competence as a plant taxonomist. In this milieu, Ownbey began his career as a botanist. Not surprisingly he began with an attempt to study and revise Castellija, an extensive and complex genus which other taxonomists had worked with for years without producing a definitive statement.

Ownbey encountered difficulties with his effort to become the authoritative specialist on Castellija, and not until much later in his life did he complete his Castellija project. Yet it was not simply problems with this genus which marked his early career, but problems with the whole approach of plant taxonomy, and the influence of a newer means for approaching this science. This influence had come into the Missouri Botanical Garden in the person of Edgar Anderson, a geneticist who had, as he put it, invaded the field of plant taxonomy in search of an explanation of the mechanisms of the evolution of species. Anderson appeared to offer a newer philosophy for taxonomy, a field which seemed to be in need of such. He called for a combination of genetics, cytology and taxonomy, with a considerable influence of such diverse fields as paleontology, archaeology, anthropology and history also represented in his approach. Anderson's approach tended to stress common weeds and agronomic plants typified by the common road-side plants of the genus Tradescantia. (See Edgar Anderson, Plants, Men and Life (Boston: Little, Brown and Co., 1952) 16-30.) Ownbey may even have assisted briefly in the famous Tradescantia project.

Anderson's influence also appeared in Ownbey's adoption of the genus Calochortus as his primary field of investigation, for this genus featured many examples of the hybridizations and combinations of genetic materials which Anderson stressed. Calochortus, accordingly, became a life-long interest. A similar generic revision was added to Ownbey investigations in the early 1940s, shortly after he had become a botany instructor and herbarium curator at Washington State University. The second project concerned the genus Allium, a diverse genus containing both natural and domestic species and again much characterized by various hybridizations. Done in conjunction with a WSU cytologist, Hannah Aase, the Allium project combined traditional methods of plant description with root-tip chromosome counts and garden experiments. It resulted in a number of papers which constituted definitive revision of the North American species of this genus. In addition to these two projects, Ownbey began work on a general Flora of the Pacific Northwest with another Missouri Botanical Garden alumnus, C. Leo Hitchcock, who by the 1940s was at the University of Washington. Ownbey also participated briefly in a war-time botanical expedition seeking pharmaceutical plants in Ecuador.

Had Ownbey continued as he started he would have been known principally as someone who had revised hybridization-prone genera and as a contributor to a regional Flora. However, an almost accidental observation in the late 1940s took his career into a considerably different direction and into the project with which he became identified in his profession. This project concerned the genus Tragopogon, an introduced plant of the American West, some varieties of which had been used as a garden vegetable. This genus was prone to hybridization and Ownbey observed it informally for several years. He first commented on it in 1946 in a letter to geneticist Charles Heiser. But not until early June of 1949 did he make the discovery that he had observed the natural evolution of new species of Tragopogon occurring in his back yard. The first known observation of a species evolving in nature, Ownbey's Tragopogon study indicated that a chromosomal doubling had occurred without human intervention and an apparently stable species had appeared. His description to a colleague carried his sense of excitement about the discovery of the polyploid Tragopogon species:

"I have been having an exciting time this spring studying the origins of species in Tragopogon through natural hybridization and amphiploidy. We have three introduced species in the Palouse area which hybridize readily whenever any two grow together. The three Fl hybrids are highly sterile but give rise on occasion to three possible amphiploid. I have been observing the Fl hybrids between the two species for several years. This spring I found their amphidiploid and with this lead worked out the rest of the story. It is easily the most spectacular case that has yet been discovered. This would apply to the first case let alone its triplication." (Ownbey to Phillip Munz, June 28, 1949)

An informal paper on the genetic behavior of Tragopogon presented these observations in the spring of 1949. The following year a more formal presentation appeared in the American Journal of Botany, at which time Ownbey assigned names and published description of the two newly-evolved species of Tragopogon. Despite the publication of the species, Ownbey felt a degree of reservation about his findings. In later publications he expressed caution about the validity of the new species, although he continued to list them. Such, for example, was his practice in Vascular Plants of the Pacific Northwest, the regional Flora produced in cooperation with his associate Hitchcock and another collaborator, Arthur Cronquist, who joined in the project in the late 1940s.

Tragopogon tended to dominate the rest of Ownbey's botanical career. His initial article of the subject quickly proved to be a classic. More writing on the subject followed closely. Then in 1954, the investigation of further phases of Tragopogon won Ownbey a Guggenheim fellowship. The fellowship enabled Ownbey to spend a year in Europe examining historical Tragopogon specimens, as well as affording time to observe some species in their native area of the Balkan peninsula. It also enabled him to establish contact with Russian, Bulgarian and Turkish botanists, who offered to find specimens of the varieties of Tragopogon found in remote areas, principally within the Soviet Union.

Ownbey returned to the United States with much information about Tragopogon, though not enough to complete a global generic survey. For several years he sought to acquire the Asian species necessary to the task, but only over a long period of time did some material become available. Even the Russian correspondents had difficulty acquiring materials, as many of the species existed in remote areas of the Caucasus and Asiatic Russia, and, possibly, they had been discouraged from cooperation with a western geneticist. Consequently Ownbey's work with Tragopogon tended to take a more specialized approach. His greenhouse and garden plantings, accordingly, came to be used by himself and a succession of graduate students as materials for examination of very specific questions about genetic mechanisms.

In the later 1950s, Ownbey partly turned his attention from the Tragopogon project to production of Vascular Plants of the Pacific Northwest. Although this five-volume work came to be more the project of Hitchcock and Cronquist, two more traditional taxonomists, Ownbey's genetic insights had an influence. Working in close association with Cronquist, who was located in New York City, Ownbey proved he could also work in traditional manners. This approach also appeared in his contribution of the section on the genus Castellija, in which he "monographed" the genus with Greenmanian thoroughness.

Through the 1950s and 1960s, a constant series of small matters concerning Allium and Calochortus had been in the background of the more spectacular Tragopogon project and the regional flora. Also, Ownbey had been administering the University herbarium during all this time, as well as teaching classes in botany. By the later 1960s the herbarium and his teaching duties began to occupy greater portions of his time, and his research activity slackened. He died in December 1974 at the age of 64. Shortly afterward, the University herbarium was named the Marion Ownbey Herbarium as a tribute to him.