Seedless plants, sometimes referred to as primitive or lower plants, include groups such as bryophytes (mosses, hornworts, liverworts), Pteridophytes (ferns), Lycophyta (Lycopodium, Selaginella) Psilophyta (whisk "fern"), and Sphenophyta (horsetails). What differentiates them from seed plants is the fact that they do not produce seeds. They do, however, form spores and sperm and eggs.

Except for the bryophytes, all of the above groups produce the vascular tissues xylem and phloem. Although considered primitive compared to seed producing vascular plants, seedless vascular plants contain xylem and phloem which connects roots, stems and true leaves. In bryophytes, the gametophyte dominates the life cycle while in the other groups, the sporophyte dominates the life cycle. Unlike the more advanced seed plants, gametophytes of seedless plants require a seasonably wet habitat for sperm to travel from the antheridium (sperm-producing structure) to the archegonium (egg-producing structure).

Although it was once thought that all seedless plants are related, it is now know that ferns belong to an entirely different group of seedless plants. Ferns, belonging in the phylum Pterophyta, are widely distributed throughout the world. In fact, most of the seedless vascular plants belong in the phylum Pterophyta. Ferns were deemed a separate group because they possess megaphylls, or large leaves with several to many veins. Plants belonging to the other groups have microphylls, or small leaves with one vein. One characteristic that all seedless vascular plants have is the presence of sporophylls. These are spore bearing leaf-like structures of the sporophyte generation. Some are quite large with several to many veins such as those seen in megaphylls and some may be small with only one vein such as those seen in microphylls.

Mosses lack true vascular tissue and are thus considered some of the most "primitive" land plants.

Observe the mosses on display.

Make a sketch of the green, leafy gametophyte and the thin, brown sporophyte.

Which phase is considered dominant? Gametophyte

Is the gametophyte dependent on the sporophyte for nutrition? No, the reverse is true

Gametes are produced at the very tips of the gametophytes. In addition, there are separate male and female gametophytes.

Observe prepared slides of moss (Mnium) antheridia and archegonia. Make a sketch below.

Once the sperm are mature, they are released and swim to the egg cell on a separate female gametophyte. The egg cell is fertilized and a sporophyte is produced.

If a gametophyte has a sporophyte growing from its tip, what sex must the gametophyte be?

Now, observe one of the spore capsules under your dissecting scope. You should be able to see a ring of teeth-like structures (peristomal teeth) which help release the spores. If they aren't evident, try removing the outer cover from the spore capsule. Make a sketch below.

Now, observe a prepared slide of a moss spore capsule and make a sketch.

Are the spores haploid or diploid? Haploid

Are they formed by meiosis or mitosis? Meiosis

If conditions are right, the spores will be released, fall to the ground, and grow into gametophytes.

Ferns take a variety of shapes and sizes from large tree ferns, such as Cyathea found in Costa Rica; small ferns with undivided leaves, such as Asplenium septentrionale; to strange looking ferns, such as Platycerium alcicome or the staghorn fern.

Examine the fern life cycle and determine which parts of the life cycle are haploid and which are diploid. Fern sporophytes grown by way of underground stems called rhizomes. Rhizomes are elongated, horizontal stems that, in the case of ferns, can grow indefinitely.

Examine one of the ferns in lab.

How may veins are present in each frond? _____Many Branching veins with one central main vein__

What types of vascular tissue make up the vein? __ xylem and phloem

Now look at the underside of the frond. Groups of sporangia called sori can be seen. Some species of fern have indusium, a specialized shield-shaped outgrowth of the fern that protects the sporangia. Haploid spores, are produced when cells within each sporangium undergo meiosis.

Remove a small portion of a leaf containing sporangia and observe under your dissecting scope.

The row of thick-walled cells along the back of each helmet-shaped sporangia is called the annulus. The annulus pops the sporangium open during dry conditions.

What do you think the function of the annulus is? A thickened band of cells in the sporangial wall that facilitates in releasing the spores

Can you see any spores in the sporangia? Yes __________________________

Next, examine a prepared slide of the fern sori. diagram and label each structure that you see. Be sure to list its function.

When fern spores germinate, they grow into a heart-shaped gametophyte.

Both sperm and eggs are formed on each gametophyte and thus they are bisexual.

Antheridia, the male sperm bearing organs, form first; then the archegonia, the female egg bearing organs are formed. The archegonia are located near the cleft of the gametophyte while the antheridia are found in more spherical structures located toward the base.

Observe a prepared slide of a fern gametophyte and make a sketch below. Label the gametophyte, antheridia, archegonia, and rhizoids.

Is it advantageous to have the reproductive structures located on the underside of the gametophyte rather than on the surface? Why or why not?

Sperm and egg are produced at different times. Why would this be a significant adaptation? So they avoid self fetilization and it promotes exchange of DNA therefore increasing the genetic diversity of the offspring.

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The zygote resulting from the fusion of sperm and egg is nutritionally dependent on the gametophyte for a short time. The sporophyte then becomes leaf-like and the gametophyte disappears. Reproduction is complete when the fronds of the growing sporophyte break through the soil in a coiled position called a fiddlehead. Once the fiddlehead unrolls, the single leaf frond is exposed.

Examine the fern gametophyte with a very young sporophyte attached. Make a sketch below.

Most terrestrial ferns exhibit homospory; they only produce one kind of spore. This spore then develops into one kind of gametophyte which produces both antheridia and archegonia. However, aquatic ferns such as Salvinia and Azolla exhibit heterospory; they produce two kinds of spores called the megaspore and the microspore. Megaspores form gametophytes with only archegonia while microspores form gametophytes with only antheridia.

Although not true mosses, club mosses, also called spike mosses, were one of the dominant plant species 3-400 million years ago. Along with whisk ferns and scouring rushes, club mosses account for most of the coal deposits found today. Unlike the now extinct huge species that dominated during the Devonian and Carboniferous periods, today’s club mosses are very small. There are 10 to 15 living genera making up approximately 1000 species of club mosses today.

Like ferns, club mosses have true leaves, roots, and stems and reproduce asexually by way of rhizomes. Lycopodium is an evergreen, and is widely distributed in tropical, subtropical and temperate forests throughout the world.

If one is available, observe the Lycopodium in the lab. The green, leafy portion is the sporophyte generation. Spore are formed in sporangia, specialized structures found either in the axils of leaves or arranged in spikes or "clubs".

Make a sketch below.

Observe a prepared slide of a Lycopodium strobilus (cluster of sporangia) and make a sketch below.

How many sporangia are produced on each strobilus? Many 20-30

In many respects, the reproductive cycle of Lycopodium is like the ferns. The spores are released, grow into small bisexual gametophytes, flagellated sperm swim to the egg, fertilization occurs and a new sporophyte is produced.

Is Lycopodium homosporous or heterosporous? Homosporous

Spores of Lycopodium are sometimes called "vegetable sulfur"- they are very flammable! In fact, they used to be used as flash powder for cameras. If material is available, ask your instructor to demonstrate.

Next examine living Selaginella plants. These plants are also called "resurrection plants" because they have the ability to dry up during dry periods and rehydrate and grow during moist times.

Observe a prepared slide of Selaginella strobili and make a sketch below.

Are the spores of Selaginella all the same size and shape? Explain.

Is Selaginella considered homosporous or heterosporous? Heterosporous

Would the gametophytes of Selaginella be bisexual or separate male and females?

This group includes the most primitive of the vascular plants. There are only two living genera, Psilotum and Tmesipteris (pronounced mes-ip¢ -tris). Psilotum, while having a widespread distribution, is a relatively uncommon plant. Tmesipteris, however, has a very small distribution and is restricted to the South Pacific. Psilotum lacks both leaves and roots and is homosporous.

Examine Psilotum and make a sketch below.

What part of the plant is photosynthetic? Green portions

Observe the small nodules found along the stems. These are the characteristic three-lobed sporangia.

Remove a mature sporangium, place some spores on a slide, and make a sketch below.

Note: if live material is not available, use the prepared slides.

Is Psilotum homosporous or heterosporous? Homosporous

Equisetum, also known as horsetail or scouring rush, is the only living genus in this group. There are approximately 15 species, most of which live in cool, moist habitats. Examine a living Equisetum plant.

Does it have leaves? Yes

Where does photosynthesis occur? Green portions

Now feel the ribbed stem of a live plant. The stem epidermis of this plant contains silica (sand). Equisetum got the name "scouring rush" because it was used to scour pots and pans by the pioneers.

The sporangia of Equisetum are grouped together in strobili, or cones, at the tip of reproductive stems.

Examine a prepared slide of Equisetum strobili. Make a sketch below.

If you look closely at the spores, you should see small appendages called elaters. These help to disperse the spores in the wind.

If they are not evident in your slide, observe a prepared slide of spore elaters in Equisetum and make a sketch below.