Winged Euonymus
Euonymus Alatus (GoBotany, Wikipedia, USDA) is a shrub growing up to twelve feet in height. It is distinctive for the corky "wings" growing along the older stems, at right angles to one another. It produces red berries in early fall (Sept.-Oct.), and if it gets enough sunlight, has leaves which will turn a brilliant red in the late fall -- hence its nickname: Burning Bush. In the woods, these are usually yellow instead.
It spreads by berry (birds) and also through tree-strike. Downed trees and branches which hit a Winged Euonymus bush will bury branches in the ground. As long as a branch isn't completely separated from the root system, it will proceed to root everywhere that it has root contact. Over time, this behavior produces thick thickets of Euonymus.
It is allelopathic, and prevents other shrubs and saplings (even other Winged Euonymus saplings) from growing underneath it.
It is found in many Acton Conservation Lands. There is a large infestation on the south side of greater Great Hill (within, and around the Yellow Trail there) which has been attacked since 2021 by a dedicated pair of volunteers.
Removal
Winged Euonymus is difficult to remove.
Larger plants may be girded (although the multi-trunk nature of Winged Euonymus means having to gird multiple trunks). They may also be cut, and then have regrowth removed multiple times, in order to kill. This generates large amounts of plant material, which should be placed into brush piles.
Smaller plants may be uprooted. Note that removal of larger Winged Euonymus bushes is usually accompanied by a large regrowth of saplings (presumably from seed), which must then be pulled.
It is strongly recommended that if a tree falls in an area with Winged Euonymus, a visit be made to ensure that the downed tree isn't creating a thicket. If there are Winged Euonymus branches pinned under a recently fallen tree, simply cut them from the bush to prevent rooting.
Common Mis-Identifications
European Spindle-tree (Euonymus europaeus, Wikipedia, USDA) This is a non-native plant which is much less invasive than the Winged Euonymous. It is likely that there are hybrids of the two as well.