Basic Biology

Bryophytes are common plants that are easily found wherever you are.

First, they are green plants—they produce their own food with photosynthesis.

They take water and carbon dioxide and use the energy in sunlight to produce sugar and oxygen.

Most of the flowers and trees you see around you have roots, stems and leaves. The roots absorb water and nutrients from the soil which are then distributed throughout the plant in a network of tiny tubes. These tubes are waterproofed by a complex sugar called lignin.

Bryophytes do not have roots, or this system of tubes lined with lignin. They have to absorb their water and nutrients directly from the surface they grow on, or from the air.

This means that most of the plant has to be very thin to allow all of the plant to be exposed to these resources.

The lack of this "plumbing system" also means that bryophytes can't grow very tall. The tallest bryophyte grows to nearly 1 meter tall, but most are smaller than a few centimeters .

Inside the cells of all of the ferns, flowers and trees on earth, there are two sets of chromosomes (2N or diploid). Chromosomes are long strands of DNA that carry the genes that tell the plant how to grow. In people, who also have two sets of chromosomes, one set comes from the mother, and one from the father. Plants are similar, so one set comes from a male plant (or a male portion of the plant), and one set comes from the female plant (or a female part of the plant). But, as you can see, there has to be at least a short part of a plant's life cycle where the pair of chromosomes split up so that the males or females can contribute their half to the offspring. This portion of the life cycle is called the haploid or 1N phase. So the life cycle of all plants makes a circle with some portion of it with one set of chromosomes-- the haploid or gametophyte phase, and some portion of it with both sets of chromosomes--the diploid or sporophyte phase.

Notice that the fern frond, the part that you think of when you think of a fern, is above the line in the diploid (2N) phase. Most people have never seen the haploid phase of a fern, which is about the size of a dime, and only survives for a short period

Notice on this chart that the part you think of as a moss is below the line and in the haploid phase. Here the diploid sporophyte is dependant on the haploid gametophyte, which is the exact opposite of the ferns and other land plants.

zygote

ferns gymnosperms

angiospermsDECREASING SIZE OF GAMETOPHYTE PHASE

green algae

bryophytes

Haploid (1N) Dominant

Diploid (2N) Dominant

Generally proscribed as 3 major groups

MOSSES About 10,000

speciesworldwide

LIVERWORTS About 7,000 species

worldwide

HORNWORTSAbout 150 species

worldwide

Moss gametophytes (1N) are organized as leaves on a stem

Most are simple and unbranched and are called ACROCARPS

Others are highly branched and are called PLEUROCARPS

The sporophyte (2N) phase is a capsule on a stalk growing on the gametophyte (1N)

SporophyteGametophyte

Mouth of the capsule after the lid falls off

The capsules come in many different shapes

The gametophyte’s body is called the Thallus and is differentiated into air chambers with photosynthetic filaments at the bottom

Each one of the little white dots on this thallus is a pore into the air chamber

There are 3 general forms:• The first is the Complex Thalloid form

If you cut through one of those pores with a very sharp blade, and looked at it through a microscope, this is what it would look like.

Photosynthetic filamentsPore into air chamber

Three general forms:• Complex Thalloid form

The sporophyte in the complex thalloid form is either elevated on a stalk growing from the thallus, or embedded in the thallus

Sporophyte

Three general forms:• The second is the Leafy form

The Sporophyte is a club like capsule on a watery stalk called a seta that grows from the gametophyteThe Gametophyte

is a stem with leaves like a moss

The sporophyte breaks open into 4 sectionsreleasing the spores and these spiral banded bodies called elaters

Three general forms:• The third is the Simple thalloid form

The gametophyte’s body is called a Thallus which is relatively homogenous--without air chambers

The sporophyte in the simple thalloid form is very similar to the leafy form—a club-like ball atop a watery stalk growing on the thallus.

The Gametophyte (1N) body is called a thallus and has a gummy bear texture

The sporophytes (2N) are needle-like horns that grow out of the gametophyte. They split from the

end downward, releasing the spores.

Where do bryophytes grow? Most people think that bryophytes grow

only in moist, shaded places. WRONG! Different species of

bryophytes can grow in different places, and on different surfaces. They can grow on dry rocks, tree bark, on buildings, on dirt, and even under water. Keep clicking to see examples of all these habitats.

Orthotrichum on dry rock

Dendroalsia on tree bark

Tortula on brick mortar Asterella on soil

Fontinalis in a flowing stream

But wait… many of those surfaces often dry out completely…

If a plant has no roots that can penetrate to some wetter place, how can it survive?

The bryophytes that grow in these dryer places have evolved to store chemicals in their cells that can be used to rebuild the cells once water is available again. This is called “dessication tolerance”

Here is a photo of a moss growing on a dry rock. The left hand side has had water poured on it. Within minutes, the left hand side has begun repairing its cells, and even started photosynthesis!