From a distance a field of tall weedy plants looks the same regardless if the bulk of the plants are Field Peppergrass or Field Pennycress.
There are other tall roadside weeds that appear similar like Shepard’s Purse and Poor-Man’s Pepper and they’d look just as weedy from afar.
Viewing the plants up close will no doubt help in identifying them. Leaf shape and whether the leaves clasp the stem are characteristics that tell the identity of these field weeds before their seeds develop.
If seeds are present,
the shapes and sizes of the seed pods can be used to tell these field and roadside weeds apart.
Field Peppergrass seed pods are like flattened balloons but more round in shape than flat. Measuring 1/8 inch (3-4 mm) wide and 1/4 inch (7 mm) long, they’re much smaller than the seed pods of Field Pennycress.
Field Pennycress seed pods are much flatter and larger and they have flattened wings to each side of a central notch at the top of each seed. Field pennycress seed pods measure 3/8 inch (10 mm) wide and 1/2 inch (12-13 mm) long.
Photos taken 18 May 2014.