Ferns are primitive plants that have no flowers or seeds and reproduce by spores. They do have vascular tissue, however -- the xylem that conducts water and the minerals dissolved in it from the roots, and the phloem that transports food from the leaves. They are classified as vascular plants and are grouped with their relatives, the whisk ferns, club mosses and horsetails, separately from the seed plants, the more highly evolved conifers and flowering plants.
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The most primitive plants, algae, live almost exclusively in water and have no need of an internal system of structures to transport water from one area of the plant to another. Mosses and liverworts are more structured than algae and may have organs that look quite similar to roots but without the woody tissue. Mosses usually have leaves that are only one cell thick and so they absorb water directly from the environment.
Ferns have leaves with at least one vein down the center and often other veins that branch, producing the typical finely divided fern frond. Some ferns have oval, entire leaves, however. The veins are responsible for transporting water and dissolved nutrients and food to the tissues of the fern. The fronds typically develop from a rhizome with roots and unfurl from curled fiddleheads to mature leaves. Spores are produced in structures called sporangia on the underside of the fronds, sometimes only on specialized fronds. The spores germinate into a small prothalus stage that produces both male and female organs. The fertilized egg then grows into a new fern.
Types of Ferns
Most ferns live in the tropics, though they have colonized every environment but the deserts. Some are quite tiny, only a few inches tall, while others, called tree ferns, develop a thick, woody stem that produces fronds at the top. Maidenhair ferns are among the most delicate, with tiny leaves on finely divided stems. Hart's tongue ferns have long, oval leaves that look like ordinary perennial leaves. Bracken ferns have running rhizomes that produce only one tall frond at each point, allowing them to colonize large areas quickly.
Most ferns like woodland conditions, with a highly organic soil, often composed of partially decayed leaves, that drains quickly but stays moist. Partial to full shade is usually ideal, though some ferns will take full sun. Some, like the licorice fern, grow on trees or rocks with very little soil beneath their roots. The key, as always, is in knowing the native habitat of each species and matching that to your garden.