74 American Midland Naturalist Monograph No. 7 



3. Stem more or less leafy, the leaves glabrous; stamens usually 6; 

 native plants. 



4. Leaflets or leaf-segments of the median and upper leaves 



oblong to oval, often toothed, the terminal one larger; 



rachis narrowly winged; wet soil. Apr.-Aug 



C. pensylvanica Muhl. 



4. Leaflets or leaf-segments of the median and upper leaves 



linear, entire, not decurrent, the terminal one similar; 



rachis not winged; moist soil. Apr.-May ....C. arenicola Britt. 



19. Arabis L. — Rockcress 

 1 . Pods erect or ascending. 



2. Stem-leaves and basal leaves pinnatifid; pods ascending, 2-2.5 

 cm long; petals 1.5-3 mm long; rocky woods and waste 

 ground; in the southern half of the state, extending to Han- 

 cock and Fulton counties. Apr.-May. [Sihara virginica (L.) 



Rollins] A. virginica (L.) Poir. 



2. Stem-leaves entire or dentate. 



3. Stem-leaves not auricled at the base, spatulate or linear, 1-3 

 cm long; basal leaves pinnatifid; pods ascending, 2-3.5 cm 

 long; petals 6-8 mm long; rocky or sandy soil; n. third of 

 111., extending southward to Henderson and Kankakee 



counties. May-July A. lyrata L. 



3. Stem-leaves auricled at the base; basal leaves entire or 

 dentate. 

 4. Mature pods erect or appressed, not more than 1 mm wide. 

 5. Pods 5-9 cm long, nearly terete; seeds almost wingless, 

 in two distinct rows; petals 3-4 mm long, cream or 

 pale yellowish; waste places; nat. from Eur. May- 

 July. Tower Mustard A. glabra (L.) Bernh. 



5. Pods 4-5 cm long; flat; seeds winged, in only 1 row; 

 petals 4-5 mm long, white or pale pink; among rocks 

 near streams; s. to Hancock and De Witt counties. 

 May-June. [A. hirsuta of Am. auth.; A. ovata (Pursh) 



Poir. (?)] A. pycnocarpa Hopkins 



4. Mature pods spreading or ascending, 1.5-2 mm wide, flat; 

 seeds winged, in two rows; petals 5-8 mm long, pink; 

 river banks, rare; Kane and Lee counties. Jime-July, 

 \A. drummondii sensu auth., non Gray; A. divaricarpa 



sensu auth., non A. Nels.] A. confinis Wats. 



1 . Pods divaricately spreading, or arcuate-recui^ved or pendulous at 



maturity. 



6. Leaves not auricled at base, lanceolate or oblong-lanceolate, 



3-12 cm long; pods pendulous, falcate, 5-7 cm long, 2-3 mm 



wide; seeds winged; petals 5-6 mm long, greenish-white; 



sepals pilosulous; wooded slopes. May-July. Sicklepod 



A. canadensis L. 



