Marcescence

Marcescence is the retention of dead plant organs that normally are shed. It is most obvious in deciduous trees that retain leaves through the winter. Several trees normally have marcescent leaves such as oak (Quercus),beech (Fagus) and hornbeam (Carpinus), or marcescent stipules as in some but not all species of willows (Salix). Marcescent leaves of pin oak (Quercus palustris) complete development of their abscission layer in the spring. The base of the petiole remains alive over the winter. Many other trees may have marcescent leaves in seasons where an early freeze kills the leaves before the abscission layer develops or completes development. Diseases or pests can also kill leaves before they can develop an abscission layer.

Marcescent leaves may be retained indefinitely and do not break off until mechanical forces (wind for instance) cause the dry and brittle petioles to snap.

Many palms form a skirt-like or shuttlecock-like crown of marcescent leaves under new growth that may persist for years before being shed. In some species only juveniles retain dead leaves and marcescence in palms is considered a primitive trait.

The term marcescent is also used in mycology to describe a mushroom which (unlike most species, described as "putrescent") can dry out, but later revive and continue to disperse spores. Genus Marasmius is well known for this feature, which was considered taxonomically important by Elias Magnus Fries in his 1838 classification of the fungi.

One possible advantage of marcescent leaves is that they may deter feeding of large herbivores, such as deer and moose, which normally eat the twigs and their nutritious buds. Dead, dry leaves make the twigs less nutritious and less palatable.

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