Special Characteristics of Ferns
Pre-Lab Discussion
Ferns belong to a group of plants that are "true" land plants. These plants have specialized tissues
called vascular (conducting or "plumbing") tissues that transport water and the products of
photosynthesis throughout the plant. For this reason, these plants are called vascular plants.
Vascular plants can grow much larger than plants without vascular tissues. When comparing
cellular organization, ferns lie between mosses and more complex vascular plants, such as trees.
Ferns belong to the Phylum Tracheophyta and grouped together into the Class Filicineae
because they produce spores instead of seeds. Plants reproducing using seeds are grouped into
the Classes Gymnospermae and Angiospermae. These two classes are distinguished from one
another on the basis of where the seeds are found on the plant (ie. cones vs. flowers).
Most ferns do not have sturdy, erect stems. Instead a thick stem runs horizontally under the soil. It
is usually covered with scales. Underground stems of this type are called rhizomes. Inside the
rhizomes are vascular tissues that carry water and food through the plant. Fern rhizomes live from
year to year. They gradually grow outward through the soil and produce numerous roots and leaves
each season. Because of the creeping rhizomes, ferns are often found in large clumps.
Unlike mosses, ferns do have true roots. Clusters of roots develop from the rhizome. They
anchor the fem in place and absorb water from the soil.
The leaves of ferns are usually large and are called fronds. The fronds die in the winter and a new
set develops from the rhizome each spring. A frond consists of 3 parts: a blade, a rachis, and a
stipe. The large expanded part of the fern is the blade. The midrib that supports the blade is the
rachis. The stipe is the stalk that attaches the rachis to the rhizome. The blade is usually divided
into many leaflets that are arranged in 2 rows along the sides of the rachis.
As new fronds develop in the spring they unroll from tightly coiled buds produced by the rhizome.
Because they look like the curved end of a violin, these young fronds are called fiddleheads. The
fiddleheads of some (not all!) ferns are edible.
When the fern is mature, raised brown dots appear on the lower surfaces of the blades. These
"dots" are called sori (singular = sorus). Each sorus contains a cluster of sporangia (spore cases).
These sporangia produce thousands of dust-like spores.
Sporangia are very sensitive to the amount of moisture in the air. Under certain conditions the
sporangia tear open and spores are shot out in a manner similar to that of sling-shot. If a spore
lands in a warm damp place, it germinates and develops into the first of cells of the gametophyte
generation.
A fern gametophyte starts as a short filament of cells with a few rhizoids to anchor it. It then
widens into a flat sheet of cells called a prothallus (pro = early; thallus a plant body). The
prothallus is heart- shaped and smaller that a dime in diameter! It has rhizoids, but no root, stems
or leaves. Most people have never seen fern prothalli, because they are so tiny and short-lived.
The function of the prothallus is to produce gametes.
Both the male and female sex organs develop on the under surface of the prothallus. The male sex
organs, antheridia are found near the apex or point of the heart-shaped prothallus, among the
rhizoids. They are dome-shaped and produce the male gametes which are spirally-coiled sperm
cells. The sperm have many flagella to help them swim to the site of the female gametes. The
female sex organs, archegonia are located near the notched end of the heart-shaped prothallus.
They are shaped like a flower vase and contain one female gamete or egg cell.
