Underwood published numerous papers in botanical journals, and was the author of
Our Native Ferns and how to study them (Bloomington, Ill., 1881; 4th ed., 1893),
Descriptive Catalogue of North American Hepaticae (New York, 1884) and “Hepaticae” in
Gray's
Manual of Botany. He also prepared together with
Orator F. Cook the
exsiccata work
An Illustrated Century of Fungi with 100 specimens (1889), the exsiccata-like series
Indiana Flora Distributed by the Biological Survey. Series I (1-100) Parasitic Fungi with 100 specimens (1894) and together with O. F. Cook the
exsiccata work
Hepaticae Americanae with 200 specimens (1887–99). Underwood's papers are maintained at the
LuEsther T. Mertz Library of the
New York Botanical Garden. ==Personal life==