Their photosynthetic cells have one large chloroplast, unlike the many smaller ones of other plants. Aquatic plants used the water, it lived in, to support its structure. Reproductive material was transported by the water to its destination. The oldest fossilized vascular plant Cooksonia was discovered in both Europe and North American Silurian rock. These are the most well represented of the seedless plants.
Most ferns have fronds, compound leaves divided into several leaflets.
As the frond develops it uncoils from a structure called a fiddle head. Ferns are homosporus with the leafy plant the sporophyte. The gametophyte is a free-living, small, fragile structure. Water is necessary for fertilization since the sperm must swim to the archogonium, where fertilization takes place. As the climate began to dry out the large Fern forests began to be replaced by a new type of plant the gymnosperm.