OP ARTS AND SCIENCES. 249 



XVII. 



CONTRIBUTIONS TO AMERICAN BOTANY. 

 By Serexo Watson. 



Presented March 14, 1888. 



1. Some New Species of Plants of the United States, with 

 revisions of Lesquerella (Vesicaria) and of the North Amer- 

 ican species of Draba. 



LESQUERELLA ; * new genus of Cruciferce. Petals spatulate to 

 oblong-obovate, entire. Filaments filiform or rarely dilated : anthers 



* The Old World genera of the Vesicaria and Alyssum group are variously 

 understood by European botanists and are very troublesome. The species of 

 Vesicaria upon which all are agreed ( V. utriculata, V. Graca and V. glabrescens, 

 the first being one of the two original species) have stout erect leafy stems from 

 a suffrutescent base, glabrous, or pubescent below with appressed 2-parted or 

 somewhat stellate hairs, with large Erysimum-like flowers, very large globose 

 coriaceous pods, nerveless septum, and wing-margined seeds. This is the genus 

 as it is generally accepted on the continent, though Boissier added an imper- 

 fectly known species which he considered as probably distinct. If it be thus 

 limited, it is certain that we have no species that can be referred to it. Bentham 

 & Hooker, however, added to it other species with globose pods, separating it 

 (so far as Old World species are concerned) apparently upon that character alone 

 from their Alyssum. These foreign species are (as Prof. Oliver informs me) 

 V. sinuata, Cretica, gnaphalodes, vestita, and probably also V. corymbosa, though 

 this is not included in Prof. Oliver's list. Of these, V. gnaphalodes and V. vestita 

 are so far differentiated from both Vesicaria and Alyssum that Boissier referred 

 them to distinct genera. V. Cretica is a peculiar suffruticose species with very 

 large coriaceous pods and toothed filaments, usually made a section of Alyssum. 

 V. sinuata and V. corymbosa, both referred to Alyssum by Boissier and others, 

 are the two species which most resemble any of our own in habit, indumentum, 

 the form and texture of the pod, etc. The species that are embraced in Alyssum 

 as one polymorphous genus by Bentham & Hooker are separated from their 

 Vesicaria upon the character of the more or less compressed pod, but also often 

 have the filaments toothed or appendaged and the cells of the pod only 1- or 

 2-seeded. These are divided by Boissier and other prominent botanists into 

 4 or 5 genera, the question of the retention of which may be left to European 

 botanists to determine. The American species differ from them all, more or 



