trimorphic [ trahy-MAWR-fik] also trimorphous [ -fus ] adjective: having three distinct forms (noun: trimorphism)
In botany, a species is trimorphic when three distinct forms of leaves or flowers are found on the same plant or on separate plants of the same species during a life cycle. A familiar example is Sassafras albidum, a native tree with three different shaped leaves: lobeless oval, two-lobed “mitten,” and three-lobed “ghost.” Their occurrence is not random. Sassafras trees tend to have fewer oval leaves on the lower crown and the lower portion of primary branches. All three leaf shapes appear to be equally distributed on vertical branches.
native Sassafras albidum in September.
Photo © Mary Free
Another trimorphic plant, Lythrum salicaria (purple loosestrife), is native to Eurasia and now invasive in the U.S. and Canada. Charles Darwin studied its three flower types, which he referred to as “long-styled, mid-styled, and short-styled” and conducted fertilization experiments on them in 1862 and 1863. He concluded that “Altogether there are three females and three sets of males, all as distinct from each other as if they belonged to different species.” (Darwin, 1864)
References
Darwin, C. R. 1864. On the sexual relations of the three forms of Lythrum salicaria. [Read 16 June] Journal of the Linnean Society of London (Botany) 8:169–171. John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online.
Hone C. 2007. Sassafras albidum. The Virtual Nature Trail at Penn State New Kensington. The Pennsylvania State University ©2002. (accessed August 12, 2021).