The 200 known species of maidenhair, or adiantum, ferns are all easily recognized due to their dark, wiry stipes or leaf stalks and delicate leaflets. The genus has colonized all continents except for Antarctica and, along with most ferns, is most commonly found in wet environments. Like all successful species, maidenhair ferns have a number of adaptations that allow them to thrive in their environment. The maidenhair ferns have adapted to surviving in very wet conditions and often grow on bare rock close to streams and in forest areas with low light intensity.
The creeping rhizomes of the maidenhair ferns allow the plant to grow on almost completely bare rock and in areas susceptible to strong runoff after rain. The rhizomes also act as a food store when the fern is unable to photosynthesize during dry or otherwise unsuitable conditions. Maidenhair ferns can become dormant and regrow leaves from the rhizome as well as reproducing asexually when sections of rhizome break off and continue to grow as a new plant. Growing rhizomes also allow a single plant to spread over a large area and continually produce new leaves, while other plants must reproduce using seeds or spores to spread.
The stiff and erect stipes of stalks of the maidenhair fern allow it to hold its leaflets above the damp ground where it prefers to have its rhizomes. The stipe also holds the leaflets above any competing plants. This adaptation allows them to photosynthesize effectively in low light conditions.
Maidenhair fern leaflets have the ability to repel water from their surface very quickly, preventing them from getting damp and rotting. The name adiantum comes from the Greek word adiantos, which means unwettable. This property is due to a waxy coating on the epidermis, or outer layer of the leaflets.
The heavily subdivided fronds and many leaflets of the maidenhair ferns allow them to cover a large area and harvest light effectively in dark conditions. Divided fronds also prevent damage in strong wind or rain.
Rather than seeds, the ferns produce spores that are light enough to be blown by the wind to new areas suitable for colonization. The maidenhair ferns have evolved membranous flaps or indusium along the lower edges of their leaflets that protect the immature spores from damage. When the spores are mature enough to be released, the flaps dry out and the spores blow away.