Ajuga
Ajuga Reptans (Wikipedia, GoBotany, USDA) a.k.a. Carpet Bugle, Carpet Weed, Bugle Weed, while pretty in a flower bed, is a nasty invasive if it escapes into the woods.
It spreads aggressively by runners that spread across the surface of the ground. It is a sprawling perennial herb with flowering stems that poke up and grow to a height of about 10 to 35 cm (4 to 14 in). The purplish-green, stalked leaves are in opposite pairs. The leaf blades are hairless and are elliptical or ovate with a rounded tip and shallowly rounded teeth on the margin.
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It isn't commonly found in Acton Conservation land, but there is a patch invading Great Hill next to 60 Piper Rd.
Removal
Mechanical removal of Ajuga is possible. It is critical to remove the roots along with the central leaves, and also pull out the runners. Frequently runners will tie to other plants.
In an area covered with leaves, it is important to move the leaves to find all the small seedlings growing nearby!