It sounds like a word to describe Martians, but actually refers to trees that hold their leaves longer than other species. There seem to be as many theories about this as the number of leaves on an average beech tree. It may be they are just moving from evergreen to deciduous and we caught them in this transition. Other ideas include dumping leaves late as an early spring fertilizer since they grow on poor soils, and as a way to catch winter snow and slowly water themselves since they live in dry habitats.
Most intriguing to me is the idea the leaves may protect the buds and young twigs. In winter the old leaves wrap like blankets to shelter new growth from the cold. And a bite of dried old leaf would discourage browsers from eating the more tasty but hidden buds. By the time they finally drop their old leaves in spring there are many other tasty foods available for hungry deer.
Because they cling so long, beech leaves stay green long after other trees have turned red and gold. In my forest there are hints of color in the maples and other trees but these beech have no sign of color. On a walk through my yard it feels now as if the seasons are mixing, each tree moving at its own pace toward autumn.