Biology (Holt)

Plants and Fungi on Land

The first multicellular organisms to live on land are thought to have
been plants and fungi living together. Such paired organisms were
able to live on land because each group possessed a quality needed
by the other.
Plants, which likely evolved from photosynthetic protists, could
carry out photosynthesis. In photosynthesis, plants use the energy
from sunlight to make their own nutrients. Plants cannot, however,
harvest needed minerals from bare rock. In contrast, fungi cannot
make nutrients from sunlight but can absorb minerals—even from
bare rock.
Early plants and fungi formed biological partnerships called my-
corrhizae (MIEkoh RIE zee),which enabled them to live on the
harsh habitat of bare rock. ,which exist today, are sym-
biotic associations between fungi and the roots of plants, as shown
in Figure 12.The fungus provides minerals to the plant, and the
plant provides nutrients to the fungus. This kind of partnership is
called mutualism. is a relationship between two species
in which both species benefit. Plants and fungi began living together
on the surface of the land about 430 million years ago.

Mutualism

Mycorrhizae

3 Life Invaded the Land

DEVONIAN PERIOD CARBONIFEROUS PERIOD

Early amphibians Early reptiles

•••••• 370 360 350 330



Second mass

extinction

Figure 12 Mycorrhizae

formed on the roots of the

first plants.This fossil is of

Cooksonia, the first known

vascular plant, which lived 410

million year ago. Cooksonia

was only a few centimeters tall.

Cooksonia’s roots formed

mycorrhizae similar to the living

mycorrhizae shown in color

to the left.

Root

Example of living mycorrhizae

Fungus

Magnification: 15x

Fossilized Cooksonia