Accompanying photos show weeds growing in full shade along our fence line. Plants exceed 3' feet in height (rail fence as scale has 4' high vertical posts). Spiky, blossomless [as of date of photos, 5/28/2015] stems protrude above leaves. Examination of Betty Marose's photo in the Sept. 2008 edition of the Maryland Master Gardener Handbook, P. 279, shows some similarity of "my" weed with her photo of Hairy bittercress, though her photo shows small white terminal blossoms. Can you identify this weed? Thanks for your assistance.
This is garlic mustard, one of the worst non-native invasive species in Maryland. Horrible problem in home landscapes. Also has taken over parks and natural areas. This is a biennial. The first year is a small plant. By the second year the crown of foliage elongates, sends up stalks of white flowers (that you must have missed) and the flowers turn into the long green seed capsules you see now.
Pull this immediately! The seed capsules explode open and shoot seeds everywhere. The seeds will remain viable and keep germinating for many years. Be sure to pull ALL THE ROOT. If you grasp it right at soil level when the soil is damp, it should come out easily. Put in the trash. Do not compost it!
You'll probably see more seedlings over the next few years. Keep an eagle eye out for them. Also, some plants will be small (just to fool you), but will still flower and go to seed. Eternal vigilance! Eventually, you can conquer it.
In the Master Garden Handbook look on page 304, photo 12.26. Info on page 298. (Hairy bittercress is a much smaller and more delicate plant. And, it's not considered an Invasive.)