EvolutionMost botanists believe that the Pteridophytes also known as ferns are descendants of the Rhyniopsida, an extinct group of free-sporing plants that originated in the Silurian period (about 430 million years ago) and became extinct in the Middle Devonian period (about 370 million years ago). Physiology The fern has no flowers, seeds and fruits. A fern is called a cryptogam, which is a plant that has no true flowers or seeds. With sporangia, receptacle in which asexual spores evolved from the leaf are formed. Physical Characteristics A fern plant generally consists of one or more fronds attached to a rhizome, which is a continuously growing horizontal underground stem. A frond is simply the leaf of the fern. The size of ferns and their fronds varies considerably between different species. The frond of the fern develops from a leaf shoot called the pastern. In most species the pastern is rolled up, with the apex of the frond at the center of the spiral. The reproductive cells of ferns are microscopic spores that are often clustered together in the brown spots visible on the undersides of the fronds. Habitat and DistributionMost There are two distinct phases in the life cycle of ferns. Once fertilization has occurred, the adult fern will begin to grow. The second phase of a fern's life cycle is the adult phase. If direct sunlight falls on the young fronds for a long period of time, the plant may die easily. When the veins are mature, moisture from the soil will be easily transported to the outer leaves and the plant will be able to withstand periods of direct sunlight. When the plant is large and mature, it will develop spores on the underside of the leaves and the life cycle of a fern will begin.