=Bitter or Tall Buttercup.= _Ranunculus acris_ L. Achenes dull, dark brown, two-beaked, somewhat lens-shaped, 3-4 mm. long, one edge very slightly convex, the other prominently so, or somewhat semicircular in outline, hem-like margin, obscure. Introduced from Europe. Low land.
=Bulbous Buttercup.= _Ranunculus bulbosus_ L. Achenes dull brown, nearly circular, diameter 3-4 mm.; beak short, turned to one side, surrounded by a narrow, hem-like margin. In June, many meadows of New England and New York are yellow with great numbers of flowers. Introduced from Europe. Upland; fortunately not yet common in this state.
=Creeping Buttercup.= _Ranunculus repens_ L. Achenes plump, dull, light-brown, nearly circular, diameter 3-4 or more mm.; beak more or less hooked, hem-like margin conspicuous. This species usually seeds very sparingly, but when once introduced, it looses no time in spreading by creeping stems. Introduced from Europe. Moist land; a rapid spreader by runners.
=Celandine.= _Chelidonium majus_ L. Yellow sap, yellow flowers; seeds dark brown to almost black, ovoid, 1.2-1.5 mm. long, with 10-12 curved vertical rows of small square depressions on each side; projecting from one side a prominent white or cream-colored ridge, irregularly wrinkled when dry. Introduced from Europe. Persistent.
=Yellow or Small Alyssum.= _Alyssum alyssoides_ L. Flowers yellow; fruit nearly circular; seeds rich yellowish brown, about 1.5 mm. long, nearly straight on one edge, flattened slightly, convex on each side or one side flat, surrounded by a thin wing. Cotyledons accumbent. Introduced from Europe.
=Yellow Rocket. Winter Cress.= _Barbarea vulgaris_ R. Br. (_Barbarea Barbarea_ L. Mac. M.) Seeds roughened, dull, light brown, irregularly flattened, broad oval, circular-oval, circular-oblong, cotyledons accumbent. Introduced from Europe.
=Hoary Alyssum.= _Berteroa incana_ (L.) D. C. Flowers white; pods oval, flattened; seeds reddish brown, circular, broad oval, or rhombic in outline, about 1.5 mm. in diameter, flat on one side showing a slight groove, the other side convex, irregular owing to pressure in the pod. Cotyledons accumbent. Introduced from Europe. A thrifty weed of the mustard family.