From AMS Glossary
A tornado that occurs with a parent cloud in its growth stage and with its vorticity originating in the boundary layer.
The parent cloud does not contain a preexisting midlevel mesocyclone. The landspout is an example of the nonsupercell tornado.
Roberts, R. O., and J. W. Wilson 1995. The genesis of three nonsupercell tornadoes observed with dual- Doppler radar. Mon. Wea. Rev.. 123. 3408–3436.