Seedless Plants - ferns and horsetails

1. division SPENOPHYTA
Horsetails is an ancient lineage of seedless plants dating back to the Devonian radiation of early vascular plants. The group reached its highest point during the Carboniferous period, when many grew as tall as 15 m tall. All that survives of this division of plants are about 15 species of a single genus, Equisetum. It is widely distributed, but is most common in the northern hemisphere, generally in damp places such as stream banks. The horsetail plant is the sporophyte generation. Meiosis occurs in the sporangia, and haploid spores are released. The gametophytes that develop from the spores are only a few millimeters long but are photosynthetic and free living. Horsetails are homosporous: the single type of spore gives rise to a bisexual gametophyte with both antheridia and archegonia. Flagellated sperm fertilize eggs in the archegonia and young sporophytes later emerge.

2. division PTEROPHYTA
From the beginning, ferns radiated into the many species that stood alongside tree lycopods and horsetails in the great forests of the Carboniferous period. Ferns are the most represented of all seedless plants. There are more than 12,000 species today. They are dicerse in the tropics and a variety of species is found in temperate forests. Fern leaves are much larger than those of lycopods and probably evolved in a different way. Those of lycopods probably evolved rom the stem that contained a small strand of vascular tissue. Leaved from this origin are called microphylls. Each leaf of a fern (megaphyll) has a branched system of veins. Megaphylls probably evolved from webbing between many separate branches growing close together. Most ferns have leaves called fronds that are compound which means each leaf is divided into several leaflets. The frond grows as its tip (fiddlehead) unfurls.