GENUS 18. 



MUSTARD FAMILY. 



167 



i. Carara didyma (L.) Britton. Lesser 

 Wart-cress. Fig. 2043. 



Lepidium didymum L. Mant. 92. 1767. 

 Senebiera didyma Pers. Syn. z: 185. 1807. 



Coronopus didymus J. E. Smith, Fl. Brit. 3: 691. 

 1800. 



Tufted, spreading on the ground, sparingly pu- 

 bescent. Stems 2'-i5' long, branching; leaves 

 deeply i-2-pinnatifid, the lower slender-petioled, 

 the upper sessile ; flowers minute, white, racemose ; 

 pedicels slender, i"-ij" long in fruit; pod didy- 

 mous, about i" broad and slightly more than i" 

 high ; valves rugose, obtuse at each end and readily 

 separating into 2 ovoid nutlets. 



In waste places, Newfoundland to Florida, Mis- 

 souri and Texas, west to British Columbia, California,, 

 Abundant in ballast about the northern seaports. 

 Also throughout tropical America and widely dis- 

 tributed in the Old World where it is native. Summer. 



2. Carara Coronopus (L.) Medic. Wart or 

 Swine's Cress. Wartwort. Fig. 2044. 



Cochlcaria Coronopus L. Sp. PI. 648. 1753. 

 Carara Coronopus Medic. Pflg. i : 35. 1792. 

 Senebiera Coronopus Poir. in Lam. Encycl. 7: 76. 1806. 

 Coronopus Coronopus Karst. Deutsch. Fl. 673. 1880-83. 



Tufted, spreading on the ground, succulent, glabrous 

 and glaucous, or with a few spreading hairs. Stems 2'- 

 15' long; leaves similar to those of the last species, gen- 

 erally larger, sometimes less divided; flowers similar; 

 pedicels stout, i" long or less ; pod 2" broad and about 

 li" high, flattish, rounded, apiculate at the summit, marked 

 with coarse wrinkles which form a crest around the mar- 

 gin; valves not distinctly separate. 



In waste places and on ballast, New Brunswick to Florida 

 and the Gulf States. Fugitive or adventive from Europe. 

 Sometimes called buck's-horn and herb-ivy. Sow-grass. Summer. 



19. THLASPI [Tourn.] L. Sp. PI. 645. 1753. 



Erect glabrous annual or perennial herbs, with entire or dentate leaves, the basal ones 

 forming a rosette, those of the stem, or at least the upper ones, auriculate and clasping. 

 Flowers white or purplish. Siliques obcuneate, obcordate, or oblong-orbicular, mostly emar- 

 ginate, flattened at right angles to the narrow septum, crested or winged. Valves dehiscent. 

 Seeds 2 or several in each cell, wingless. Cotyledons accumbent. [Greek, to flatten, from 

 the flat pod.] 



A genus of about 25 species, natives of temperate, arctic and alpine regions. In addition to the 

 following, 2 others occur in arctic America, the Rocky Mountains and California. Type species : 

 Thlaspi arvense L. 



Lower stem-leaves not clasping ; seeds rugose. 



All the stem-leaves cordate-clasping ; seeds smooth. 



1. T. arvense. 



2. T. perfoliatum. 



