Glossy Buckthorn

Frangula alnus, a.k.a. Rhamus frangula ( USDA, Wikipedia, GoBotany, IPANE )

Glossy Buckthorn, a small tree or coarse shrub that grows up to 20 ft. tall, is one of the most common invasive plants in Acton.  Its simple leaves leaves are 1 - 2.5 in. long, have untoothed edges and are usually arranged alternately although they may appear almost opposite near the branch tips. The leaves are dark green (in the summer) and glossy above, with either no hairs or slight hairs beneath. The leaves turn greenish-yellow to yellow late in the fall, and remain on the plant when most other species have already lost their leaves.

Young stems are greenish, often with soft fine hairs. Older bark is grayish-brown, with prominent light raised lenticels. Despite the name, it has no thorns. The heartwood (visible when cut) is pinkish to orange in growth over a couple of years old. The roots are deep red.

It flowers with clusters of one to eight 5-petaled yellow-green flowers after the leaves expand, from May to August.  The berries are round and roughly 0.25 in diameter.  They change from red to black as they ripen, from July to August.  It should be noted that at any given time there can be flowers, partially ripened fruits (red) and fully ripened fruits (black) present on the same plant.
TBD