Biology Reference
In-Depth Information
Lichens
A lichen is a fungus body, usually one of the
Ascomycetes with apothecia, enclosing a green
or blue-green alga. The fungus receives some
food from the alga and the alga some food and
protection from the fungus, a relationship termed
symbiotic. Lichens frequently grow on living
trees and shrubs, but their injury is indirect, an
interference with light or gas exchange to stems
or foliage, rather than from penetration of living
cells of the suscept plant. There are three types
associated with plants: crustose, a crust closely
appressed to bark of main trunk or larger limbs;
foliose, leaflike, prostrate but not so firmly
attached to the substratum; and fructicose,
bushlike, erect or hanging.
Lichens are more abundant on garden
shrubs - boxwood, camellias, azaleas, and so
on - and on citrus in the South. They flourish
in neglected gardens and orchards, and in shady
damp locations, and may sometimes kill twigs
andbranchesofweaktreesgrowingonpoor
sites.
In most gardens control is unnecessary. If
lichens become too disfiguring or too abundant
for plant health, they may be killed by spraying
affected parts with bordeaux mixture or other
copper spray; spray when the lichens are dry.
They may be removed from main trunks by
rubbing the bark with a steel brush after they are
softened by rain.
