1920] Wiegand,— Variations in Lactuca canadensis 9 
VARIATIONS IN LACTUCA CANADENSIS. 
K. M. WIEGAND. 
THE treatment of Lactuca canadensis L. and its forms in our various 
manuals seems not to accord exactly with what is found in the field. 
The writer has attempted a different classification of these variations, 
and the result is presented in the accompanying key. In floral and 
fruit characters L. canadensis is remarkably constant. It is only 
in the leaves that great fluctuation is found. Here variation is 
marked, as it often is in the ligulate Compositae. 
The var. typica and its three following varieties are not equally 
related. The last three varieties are phases of one polymorphic 
subdivision of the species. "This subdivision is to be set off against 
var. typica. These two primary divisions intergrade but little, and 
have slightly different, though overlapping ranges, the typical form 
not extending so far south. In the second group the varieties and 
forms show abundant intergradations. In the entire-leaved varieties, 
the lobed leaves have been wholly replaced, while in the obovate 
toothed-leaved variety the oblanceolate or obovate toothed basal 
leaves, frequently found in var. integrifolia, have spread over the 
whole plant. It is as though in one case the leaves were pushed 
toward the base of the stem through the multiplication of the upper 
entire leaves, while in the opposite case the lower leaves have entirely 
replaced the upper. The lobed leaves immediately below the entire 
ones in var. latifolia have broadly faleate divisions, while the lower- 
most on the same plant usually have the divisions obovate, sub- 
truncate and toothed. When these lowest leaves are entirely elimi- 
nared through the multiplication of the entire leaves, the only divided 
leaves remaining are those with broadly falcate divisions. Unless 
this relation is understood the grouping together under one varietal 
head of plants apparently so dissimilar may be a trifle confusing. 
The description of L. canadensis given by Linnaeus leaves the 
impression that he had in hand a form with unlobed leaves, since 
a character so striking would naturally have been mentioned. The 
species was based on a specimen of Kalm's. This Dr. Gray saw, 
and at that time made the note that it was the L. elongata of authors. 
Since Dr. Gray recognized a species integrifolia, it is to be presumed 
