The Collaborative International Dictionary
Yellowseed \Yel"low*seed`\, n. (Bot.) A kind of pepper grass ( Lepidium campestre).
Wikipedia
Lepidium campestre (field pepperwort or field pepperweed) is an annual plant in the Brassicaceae or mustard family, native to Europe, but commonly found in North America as an invasive weed. The most notable characteristic of field pepperweed is the raceme of flowers which forks off of the stem. These racemes are made up of first small white flowers and later green, flat and oval seedpods each about 6 mm long and 4 mm wide. Each seedpod contains two brown, 2.5 mm long seeds.
The stem of field pepperweed comes out of a basal rosette of toothed leaves. The stem is covered in leaves, which are sessile, alternate and arrow-shaped. The entire plant is generally between 20 and 60 cm tall and covered in small hairs.