130 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
that seeks to explain the cause or mechanism of species forma- 
tion in Lesquerella. 
Taxonomic History oF LESQUERELLA 
Position of Lesquerella among Other Genera of the Cruciferae.— 
There have been three rather recent treatments of the American 
genera of this family in which an endeavor was made to observe 
phylogenetic sequence. Prantl in ‘Die Natürlichen Pflanzen- 
familien’ united six genera of more or less similar aspect into 
the subtribe Physariinae of the tribe Schizopetaleae. These 
genera are Synthlipsis, Lyrocarpa, Dithyrea, Physaria, Lesquerella, 
and Phoenicaulis. Robinson in Gray’s ‘Synoptical Flora of 
North America’ retained this group with the exception of Phoeni- 
caulis, under the tribal name of Physarieae. Von Hayek, in 
the most recent review of the family as a whole (Beih. Bot. Cen- 
tralbl. 27: 310. 1911), preserves the designations and ranks 
proposed by Prantl, but transfers Synthlipsis to another sub- 
tribe of the Schizopetaleae and adds Mancoa, Agallis, Sphaero- 
cardamum, Stenonema and Notothlapsi to the subtribe Physar- 
iinae. For Lyrocarpa he erects a separate subtribe. In a dia- 
grammatie representation of the phylogeny of the tribe he de- 
rives Lesquerella from Mancoa and from Lesquerella he derives 
Physaria. This latter supposition is confirmed by the present 
study. The reason for relating Lesquerella to Mancoa is not 
evident. This latter genus is represented by a single annual 
species in the Andes of Peru and Argentina. It is further char- 
acterized by elongated, somewhat obcompressed, pubescent 
pods, and white flowers. Because of the obcompressed pods of 
the species in the section Enantiocarpa they have been referred 
by some authors to the genus Synthlipsis. As stated in another 
part of the present study, it is not believed that these species 
are at all related to the type of Synthlipsis. In fact, Physaria 
is the only genus that may with confidence be associated with 
Lesquerella at the present time. In any search for the group 
from which Lesquerella has been evolved the most primitive 
characters must be constantly borne in mind as well as the 
probable point of origin. What the ancestral genus was we do 
not yet presume to say. 
Previous Taxonomic Treatments of the Species of Lesquerella.— 
The first species of this genus to be definitely recorded by science 
