Mosses

Do you know what plant has been used for dressing wounds, padding diapers, and sealing walls? Yes: Moss. A very useful little plant. About 450 million years ago the first land plants developed: Bryophytes and ferns. The first land plants reproduced - just like the algae and bacteria living in the sea at that time - by spreading spores instead of seeds.

And they still do. They are spore plants. Bryophytes are divided into three groups. Mosses, Liverworts and Hornworts. Hornworts are a bit special, so let's focus on mosses and Liverworts.

There are many varieties of moss, for instance, Peat Moss. Mosses have Gametophytes: male plants carrying sperm and female plants carrying eggs. How do you think the sperm get to the eggs? Well, with the aid of rain they swim over to the egg cell. And now what?

This sperm has fertilized an egg and something is growing on the female gametophyte. Does that mean that the moss's reproduction is done? No, not yet. Moss has one step left before the process is over. Bryophytes are spore plants, remember?

So this, that looks like a ball on a stalk, is a: sporophyte. On top of this stalk, the seta... sits the spore capsulum, in which the spores mature. When the spores are mature, the capsulum bursts and the spores are spread by the wind. And it's not until the microscopic spores land that new moss can grow.

The life cycle of moss is complete. So moss reproduction has two steps. First: sexual reproduction through the gametophytes, and second: asexual reproduction through the sporophytes. Complicated? Well, it has worked well for some 450 million years, but moss can also reproduce in a simpler way.

Sometimes part of a moss plant detaches and starts growing in a new place. Cloning! But, if bryophytes are so different from seed plants, why do they look so similar? Mosses also have leaves, stems, and roots, don't they? No, actually not.

These, though they look like roots - are actually something else. They are thin threads that anchor the moss to the ground. They are not sucking up water like real roots do. These threads are called Rhizoids. And these - that may look like leaves - are so-called false leaves.

The false leaves on moss are called microphyll. Let's look at this sunflower. It sucks up water and minerals with its roots and transports them through vessels in the stem and leaves. Other vessels transport sugar from the leaves. This is why flowers and other plants are called vascular plants.

Bryophytes have no vascular system. So how do mosses drink? Mosses absorb moisture and water directly from the air, through their microphylls and their false stem. Because mosses absorb water directly from the air, they are very sensitive to air pollution. Mosses live in moist areas where they cover the ground like a soft carpet.

This makes the soil below them moist and less likely to be washed away by rain. In this way they prevent... erosion. So they are great for the environment. But what about Liverworts, how do they look?

Like this. Just like moss they have rhizoids instead of roots, and false leaves. And they reproduce in the same way as moss - sexually by gametophytes and asexually by sporophytes. But instead of mosses' tiny microphylls, Liverworts have one large false leaf: a Thallus. All bryophytes create their own food and energy through photosynthesis, which of course means that they add oxygen to the world.

As we said earlier: very useful little plants.