A SYSTEMATIC STUDY OF THE NORTH AMERICAN 
GENUS TRILLIUM, ITS VARIABILITY, AND ITS 
RELATION TO PARIS AND MEDEOLA 
R. GATE 
Formerly Research Assistant to the Missouri Botanical Garden 
INTRODUCTION 
Trillium is a genus in which remarkable uniformity in 
general appearance and structure is combined with great 
variability in certain organs from species to species. This 
variability is of such a nature that it is often difficult to 
delimit the species accurately according to present knowledge. 
While the range of variation, in leaf characters, for example, 
is so slight in the genus that a single leaf can in nearly all 
cases be recognized at sight as belonging to Trillium, yet in 
many cases it would be quite impossible to determine with 
certainty the species. 
The present paper may therefore be regarded as a con- 
speetus of the North American species of Trillium—thirty-one 
of which, with nine varieties, are recognized—without an at- 
tempt to delimit in many cases the exact boundaries of indi- 
vidual species. This can only be done satisfactorily after 
further extensive field studies of the range of variation in a 
number of the species. 
Trillium is of particular interest from another point of 
view. A number of its species have long been known to give 
rise to striking variations, such as double flowers, extra leaf 
whorls, increase in number of parts in a whorl, ete. The 
references to such cases are very scattered in the literature, 
but in the second part of this paper an attempt is made to 
bring them together. While it is quite certain that there 
are omissions, yet it is hoped that all the more important 
records have been included. The remarkable variations of 
T. grandiflorum have been most extensively studied, but 
cases in which extra whorls of leaves occur are perhaps of 
greater phylogenetic interest. Instances in which a double 
flower continues to be produced from the same rootstock year 
ANN. Mo. Вот. GARD., VOL. 4, 1917 (43) 
