(adj.) of a leaf, decaying but remaining attached to a tree
A leaf that withers in the autumn, but remains attached to a tree or plant through the winter months, is a marcesent leaf; the process or phenomenon by which that happens is called marcescence.
That’s a word that has also come to be used more figuratively of anything that decays or begins to fail, or else proves only fleeting or ephemeral. In its original ecological and botanical sense, though, it dates back to the early eighteenth century, and was first recorded in the English lexicographer Nathan Bailey’s Universal Etymological English Dictionary way back in 1727 .
At its root (no pun intended) is a Latin word marcescere, which essentially means ‘to begin to wither’ and derives in turn from an earlier verb, marcere, likewise meaning ‘droop’ or ‘faint’. (Strictly speaking, marcescere is the so-called inchoative, or inceptive form of marcere—in other words, it specifically refers to the process of withering beginning to occur, especially of its own volition.) It’s a root that doesn’t have many descendants in English today, but in the same etymological gene pool are the likes of macrid (an adjective describing anything that appears withered or decayed), and marcor (an old-fashioned word for a state of emaciation).
But in more practical terms, what is the purpose of a marcescent leaf? Some trees (like beech and oak) exhibit marcescence more readily than others, and will keep a great many of their leaves throughout the winter months, despite being deciduous. But if the whole point of trees shedding their leaves in winter is to essentially conserve energy, what benefit is there in retaining a covering of dead leaves?
The reason for it is unclear, but it could be that the leaves, despite their withered condition, still provide some element of protection from winter frosts—or perhaps from larger grazing animals, like deer, that would strip bark from the trees boughs, and consume its bare buds come the springtime.
In some trees, of course, occasionally a single leaf or two will simply never quite disconnect from its branch, and will remain attached while all the others fall. In those instances, marcescence is simply a result of happenstance—and unwittingly makes a nice metaphor for enduring the long winter months as best we can.