From semi- + dwarf.
semidwarf (plural semidwarfs)
- A plant that grows to a lesser height than usual for its kind, but taller than a dwarf variety.
2008 April 17, Leslie Land, “Veggies in the Shade”, in New York Times[1]:Although Miss Kim is often described as semidwarf, this popular late bloomer can become 9 or 10 feet tall.