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.
Identification by Leaf
Two plants that can be mistaken for buckthorn are sweet-pepperbush and winterberry. The best way to discriminate is to look at the underside of the leaves:
Buckthorn and Sweet Pepperbush have well defined veins that curve toward the leaf tip (mature buckthorn has 8-9 veins). But Sweet Pepperbush leaves have teeth and buckthorn leaves do not.
Winterberry leaves do NOT have 8-9 well defined veins, and have teeth as well. For small plants, buckthorn and low bush blueberry can sometimes be confused when viewed from above, but the underside of low bush blueberry leaves do not have well defined veins. Generally, plants that might be confused with buckthorn, other than sweet pepperbush, do not have well defined veins when the underside of the leaf is viewed.
Identification by Bark
TBD
Identification by Buds In Winter
TBD
Identification by Twigs
TBD