36 Nebraskaland • April 2020
less familiar cup fungi, which includes the molds and rusts,
but also the delicious morel. The algal partners are mainly
green and blue-green algae, single-celled organisms that
contain chlorophyll for photosynthesis.
When a lichen-forming fungus comes in contact with the
appropriate type of alga, it envelops the alga cells. Once the
cells are captured, the fungus undergoes a transformation,
forming a thallus, the main body of the lichen. Depending on
the lichen species, the alga cells either form a layer near the
upper surface or are dispersed throughout the thallus.
The main growth forms of lichens are crustose, foliose
and fruticose. Crustose lichens, which are the most common
type in our region, are fl at and crust-like, and adhere tightly
to their substrates such as rock or bark. The less common
foliose lichens are leaf-like and spreading and adhere more
loosely to their substrates. Fruticose lichens, uncommon in
our region, are often upright and shrubby or hang in long
narrow strands, mainly from trees.
In the past, lichenologists thought the partnership
between a fungus and an alga was mutually benefi cial. They
now believe that, in many cases, it is more of a parasitic
relationship, in which the fungal partner is the principal
benefi ciary, extracting and using sugars from the algae
produced through photosynthesis. Put more simply, the fungi
might be enslaving the algae for food production (typically
fungi obtain their food by decomposing organic matter).
Strangely, algal cells, when confi ned within a lichen, become
leaky and exude sugars for the fungus to absorb.
The algae do receive something out of the bargain, mainly
a relatively safe place to live within the lichen where they are
Hooded sunburst lichen grows on the bark of an ironwood
tree in moist deciduous woodlands in the central Niobrara
River Valley in Brown County.
