At the University of Idaho between 1923 and 1928, Clark held an assistant professorship in botany while beginning to lay the groundwork to conduct her own research on Heptaicae.

[5] Clark's extensive research career on Heptaicae, which consumed the latter half of her life, would have her categorize and label numerous plants, mosses, and liverworts that were undocumented in the Pacific Northwest and beyond.

[5] She also wrote Her most notable contribution was a five-part series on The Hepaticae of North America, which she helped complete alongside Frye between 1937 and 1947.

[7] Clark and Frye also received Heptaicae specimens from Alaska which they identified at the University of Washington and published an article in The Bryologist on their findings in June 1942.

They also had difficulty processing the Alaskan biological material because they parties responsible, in their opinion, did not bother to separate larger plants from smaller ones and, "almost all of the collecting has been done by those who do not know a moss from a liverwort, and who were not primarily interested in bryophytes.

"[8] Clark and Frye go on to describe the qualities that are desired for a good collector of Heptaicae in order to demonstrate the point that these samples were not collected carefully enough.

Their work, conducted at the University of Washington, closely detailed and classified these specific species of the genus Frullania that were located from several South American countries and Mexico.