A MONOGRAPH OF THE GENUS LESQUERELLA' 
EDWIN BLAKE PAYSON 
Formerly Teaching Fellow in the Henry Shaw School of Botany of 
Washington University 
GENERAL MorPHOLOGY AND PHYLOGENY 
The Cruciferae are especially interesting from a phylogenetic 
point of view because o! the importance that attaches to what 
seem to be minute characters. The greatest students of the 
subject have failed to find many points of agreement, and there 
is much confusion in regard to even the broad lines of relation- 
ship within the family. It is, of course, a most homogeneous 
group, and the same variations have occurred independently 
time and again, thus giv ng rise to similar forms that are not of 
necessity analogous. I; becomes increasingly evident that 
before any satisfactory grouping within the family can be made 
every genus must be stuilied critically and its connections traced 
to other genera. It is of fundamental importance to know which 
species within a group are the primitive ones and which represent 
terminal branches. When much reliable data of relationship 
within small groups have been accumulated, and only then, 
may the parts be finally pieced together, unless perhaps too 
many intermediates have been irrevocably lost. From present 
indications, however, an optimistic view may be held with re- 
gard to the final solution. In the following treatment of the 
genus under consideration there have been assembled in para- 
graphs dealing with particular organs or tissues the various 
phylogenetic conclusions arrived at and some of the arguments 
in favor of the different hypotheses. These conclusions, it is 
believed, point the direction of development in the genus Les- 
querella, but are not necessarily to be relied upon for any other 
enus. 
Habit of Growth—There are within the genus a few species 
entirely herbaceous and, under any but the most favorable con- 
ditions, certainly annual. Several others have attained an 
extreme annual condition and pass most of their life within the 
1 Issued Jan. 14, 1922. 
ANN. Mo. Bor. Garp. Vor. S, 1921. (103) 
