Ferns are ancient plants that have proved adaptable and resilient. Ferns grow on sea-sprayed cliffs, in the crevices of rocks and bluffs, in lakes and rivers, in high mountainous regions and even in semi-deserts. They grow most abundantly, however, in the shady, moist understory of temperate forests and in rainforests at all latitudes, where they often grow on trees.
Of the 10,000-12,000 species of ferns and "fern allies" living today, only 69 are found in Missouri. Fern allies are species of plants that have been historically grouped with the true ferns because of similarities in reproduction and their internal systems for the circulation of water and food. These species include horsetails or scouring rushes (Equisetum), quillworts, and spike (Isoetes) and club mosses (Lycopodium and Saliginella).
Missouri's ferns and fern allies can be traced to ancient climatic or geographic connections to northern forests, to dry regions of the southwest and to the moist, warm tropical forests of the Central America and the Caribbean.
Hay-scented fern (Dennstaedtia punctilobula) and club mosses (Lycopodium), for example, once grew throughout boreal forests. The purple cliff brake (Pellaea atropurpurea), the lip ferns (Cheilanthes spp.) and the rock spikemoss (Selaginella rupestris), on the other hand, have southwestern relatives, and the resurrection fern (Polypodium polypodoides var. michauxianum) has tropical roots. The kinds of conditions ferns are growing under can be clues to where the ferns came from.
It is easy to identify most Missouri ferns by their unusual leaves or fronds-slender stalks (stipes), together with their much divided, lacy and delicate leaf blades. There is considerable variation among fern leaves, however.
The leaves of walking fern (Asplenium rhizophyllum), for example, have long tapering, undivided blades while those of bracken fern (Pteridium aquilinum) are divided into three blades. Fern leaves range in size from under 1/16" in the eastern mosquito fern (Azolla caroliniana) to just under 5' in the larger ferns-bracken, log, cinnamon and royal.
Unlike mosses and algae, ferns and fern allies have a vascular system for carrying nutrients and water throughout their roots, stems and leaves. And, unlike flowering plants, they do not have flowers, fruits or seeds.
How ferns reproduced without flowers and seeds remained a mystery for many centuries. During medieval times, people believed that ferns produced flowers and seed invisible to the human eye.
By the mid-18th century, scientists had discovered that fern "seeds" were actually very small spores produced in tiny, one-cell thick capsules