104 KEY AND FLORA 



1. B. alba Boiss. WHitE Mustard. Stem 2-5 ft. high, with 

 reflexed hairs. Upper Ifeaves pinnately cut. Pods borne on spreading 

 pedicels, bristly, with a sword-shaped, 1-seeded beak occupying more 

 than half their length. Seeds pale. Cultivated from Europe and 

 introduced to some extent. 



2. B. arvensis Ktze. Charlock. Stem 1-2 ft. high ; it and the 

 leaves rough-hairy. Upper leaves rhombic, barely toothed. Flowers 

 ^-| in. across, somewhat corymbed, bright yellow. Pods knotty, 

 spreading, at least |. of each consisting of a 2-edged, 1-seeded beak. 

 A showy, troublesome weed in grain fields. Naturalized from Europe. 



3. B. juncea Cosson. Similar to the preceding, but nearly or 

 quite smooth. Pedicels slender. Beak slender, conical, not contain- 

 ing a seed. Naturalized from Asia and becoming very abundant 

 eastward. 



4. B. nigra Koch. Black Mustard. Stem 3-6 ft. high, some- 

 what hairy. Lower leaves lyrate, with the terminal lobe much the 

 longest; stem-leaves linear-lanceolate, entire or toothed, smooth. 

 Pods awl-shaped, 4-angied, smooth, lying against the stem ; seeds 

 brownish, more biting than in No. 1. Cultivated from Europe and 

 introduced. 



Vni. SISYMBRIUM L. 



Annual or biennial herbs. Eadical leaves spreading ; stem 

 leaves alternate, often eared at the base. Mowers in loose 

 racemes, usually yellow, often braeted. Pods generally nar- 

 rowly linear, cylindrical, or 4-6-angled ; seeds many, ellipsoid, 

 not margined. 



1. S. officinale Scop., var. leiocarpum. Hedge Mustard. Stems 

 branching, stiff. Leaves runcinate-toothed or lobed. Flowers very 

 small, pale yellow. Pods somewhat 6-sided, awl-shaped, smooth, 

 closely pressed against the stem. An unsightly weed in waste ground. 

 Naturalized from Europe. 



2. S. canescens Nutt. Tansy Mustard. Stem 1-2 ft. high. 

 Leaves twice pinnately cut, usually covered with grayish down. 

 Flowers very small, yellowish. Pods oblong, club-shaped, 4-angled, 

 borne on pedicels projecting almost horizontally from the stem, in 

 long racemes. Common westward. 



IX. RADICULA Hill. (RORIPA) 



Annual or biennial, mostly aquatic plants. Stems erect or 

 diffuse, often widely branching. Leaves simple, pinnately 

 lobed. Flowers small, white or yellow. Sepals spreading. 



