Ferns, like trillium, Jack-in-the-pulpit and other forest floor-dwellers, make lovely plants for shady places. Ferns are members of pterophyta, a family on a middle step on the evolutionary ladder; they are vascular plants that use a primitive form of sexual reproduction. The life cycles of these primitive plants, unlike those of their flowering angiosperm cousins, contain two distinct generations of plants.
Ferns first appear in the fossil record during the Carboniferous Period more than 300 million years ago. Their remains formed the first deposits of the coal and oil that we rely upon as fossil fuels. Ferns were descendants of early plants that developed the process of photosynthesis; they used carbon dioxide and “exhaled” oxygen. Some early ferns produced seeds; their descendants became the flowering plants. Today’s ferns are descended from more primitive forms that passed through distinct sporophyte and gametophyte generations before forming a new plant.
Ferns are vascular plants that draw nutrients in their roots from the soil and process carbon dioxide and water using sunlight gathered on the surfaces of their leaves, called fronds. The plant we call fern is actually just one part of the plant’s life--the sporophyte generation. Ferns grow from rhizomes that are thick roots. Their roots can be divided for vegetative reproduction. Ferns begin sexual reproduction by using cellular divisions called spores that collect in bundles called sori underneath their fronds.
Groups of spores called sporangia fall from fronds onto the ground, where they grow into gametophytes, asexual carriers of the female eggs, or archegonia, and male antheridia containing sperm. Antheridia must travel through water to meet the archegonia. Gametophytes are not self-pollinating; sperm must travel to eggs from adjoining gametophytes. Gametophytes with their archegonia antheridia use everything from flood waters to the moisture in decaying matter and water in animals’ coats to travel to their new homes.
While unfertilized eggs may form new gametophytes, fertilized eggs become zygotes, tiny, complete cells that begin dividing to form the rhizome. Little fronds uncurl from the top of this root, and finer roots grow from its bottom, anchoring in the soil. Since fertilization depends on moist conditions, most ferns begin life in damp environments like woods, stream sides and wetlands.
Ferns grow according to their genetic code. When mature, plants begin dividing cells and producing sporangia to reinitiate the reproductive process. Cross-fertilization and adaptations triggered by climate changes may create new varieties; some modern ferns grow in full sun or hot climates but still require water for the gametophyte phase of reproduction.