168 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



16. ARABIDOPSIS (DO.) Schur. 



1. Arabidopsis thaliana (L.) Biitton. Mouse-ear cress. 



Fields; common. March-May. Native of Eur. and Asia; widely naturalized in 

 N. Amer. {Sisymbrmm thalianum Gay; Stenophragma thaliana Celak.) 



17. CAMPE Dulac. Winter cress. 



Lobes of the leaves mostly 4-S pairs; pods stout, shai-ply angled, on very stout short 



pedicels 1. C. vema. 



Lobes of thg leaves mostly 1-4 pairs; podsslendert>r stout, obtusely angled, on slender 

 pedicels. 



Pods erect; petals pale yellow 2. C. stricta. 



Pods spreading or ascending; petals bright yellow 3. C. barbarea. 



1. Campe vema (Michx.) Heller, 



Woods, fields, and waste ground; abundant. Native of Eui'.; extensively natural- 

 ized in eastern N. Amer. (Barbarea praecox R. Br.; B. vema Aschers.) 



This and the other species are much used as "greens," and are commonly seen in 

 the markets in spring. 



2. Campe ^icta (Andrzej.) W. F. Wight. 



Fields; abimdant. Apr .-May. Native of Eur. Asia, and northern N. Amer.; Avith 

 us doubtless adventive. {Barbarea vulgaris of Ward's Flora; B. stricta Andrzej.) 



3. Campe barbarea (L.) W. F. Wight. 



Fields; apparently not common, Apr. -May. Native of Eur. and northern N. 

 Amer. ; naturalized in eastern N. Amer. {Barbarea vulgaris E . Br. ; B. barbarea MacM.) 



18. ARABIS L. Rock cress. 



Lower leaves pinnately divided; stem leaves mostly linear and entire, tapering at the 



base. Pods ascending 1. A. lyrata. 



Lower leaves merely toothed; stem leaves all or mostly broader than linear, often 

 toothed. 

 Stem leaves, at least the upper ones, long-tapering at the base, not auiicled, more 



or less toothed ; pods drooping. Plants hairy 2. A. canadensis. 



Stem leaves never tapering at the base, more or less clasping and auric! ed; pods 

 ascending or spreading. 

 Plants glabrous throughout; upper leaves mostly enthe, long-tapeiing at the 



apex. Pods recurved-spreading 3. A. laevigata. 



Plants haiiy, at least below; upper leaves all or nearly all conspicuously toothed, 

 never long-tapering at the apex. 

 Petals more than twice as long as the calyx; pods strongly ascending; seeds 



narrowly winged 4. A. patens. 



Petals equaling or very slightly exceeding the sepals; pods spreading; seeds 

 not winged 5. A. dentata. 



Arabis hirsuta (L.) Scop, was reported from Sandy Landing by TVard, but the species 

 is not represented by specimens from our region. 



1. Arabis lyrata L, 



On rocks along the upper Potomac; fi'equent; also collected once along the Eastern 

 Branch, probably adventive there. March-June, Widelj' distributed in N. Amer ; 

 also in eastern Asia. 



2. Arabis canadensis L. Sickle-pod. 

 Woods along the Potomac and Rock Creek; frequent. May- June. Eastern U. S. 



3. Arabis laevigata (Muhl.) Poir, 



Woods, often on rocks; frequent along the upper Potomac, occasional elsewhere. 

 Apr.-May. Eastern N. Amer. 



