Оноклея чувствительная: описание и особенности вида

Species of fern

Onoclea sensibilis, the sensitive fern, also known as the bead fern, is a coarse textured, medium to large sized deciduous perennial fern. The name comes from its sensitivity to frost, the fronds dying quickly when first touched by it. It is sometimes treated as the only species in Onoclea, but some authors do not consider the genus monotypic.

The sterile and fertile fronds of Onoclea sensibilis have independent stalks originating from the same rhizome, quite different from other ferns. The sporophylls (fertile fronds) are smaller, 20–45 cm (8–18 in) in length, like beads, on upright fertile fronds, hence the common name Bead fern. Sori are typically bilaterally symmetrical, though leaf forms have been observed with pinnae fertile only on a single side of the rachis. This form, named O. sensibilis L. F. hemiphyllodes (Kiss & Kümmerle, 1926) and a second, O. sensibilis L. F. obtusilobata having flat pinnules (not curled or bead shaped), Spores are monolete with the antheridium, or sporangium, containing either 32 or 64 sperm spores, The small fertile margins, that in live form held spore in tightly rolled structures, maintain their dry, leathery shape over winter. These pinnules respond to spring's higher humidity by opening, releasing their spore into the air. Subsequent gametophytes are unisexual in early development, favoring cross fertilization, later becoming bisexual to ensure species survival.

The genus Onoclea was cast by Carl Linnaeus in 1751, separating from the fern's prior association with the Angiopteris genus. The binominal name, Onoclea sensibilis, was published in his 1753 Species Plantarum.

The Onoclea sensibilis plant has remained essentially unchanged over millions of years. A fifty seven million year old fossil of Paleocene epoch flora shows specimens virtually identical to modern samples. Its deciduous fronds do not tolerate freezing temperatures, however, the plant survives USDA hardiness zones 4–8, Winter survival is enhanced if the dried frond petiole bases are left intact. Onoclea sensibilis is a wetland indicator, listed as a Facultative Wetland Hydrophyte in the 2013 (US) National Wetland Plant List due to its observed affinity for wetter soils. Opinion is mixed regarding the species' tolerance to disturbance of its growing environment. In one forest setting, a decade long decline was noticed following even single cut tree felling operations. In other settings sensitive ferns appear opportunistic, disturbance not being a problem. Chirosia gleniensis fern miners and the larvae of sawflies Hemitaxonus dubitatus feed on its leaves. Larvae of moth species Phlogophora iris (olive angle shades, pictured), Callopistria cordata (silver spotted fern moth) and Uredinopsis mirabilis, Invasive fungi like Taphrina filicina, can infect leaves, causing blisters or white powdery mildew. Fungi can develop beneath beech trees, where aphid honeydew secretions accumulate; these strictly epiphyllous honeydew fungi, Sclerotiomyces colchicus and Scorias spongiosa (Schwein.) Fr., have been recorded on Onoclea sensibilis, where their sooty mold buildup impairs leaf function.

Onoclea sensibilis has two internally synthesized chemical defenses against insects. Ingesting any part of the plant introduces thiaminase enzymes and phytoecdysteroid hormones which can disrupt an insect's molting cycle, preventing its full development.

Onoclea sensibilis has been implicated in equine poisoning and death, especially if eaten in quantity. Its summaries, however, frequently include precautionary statements that ferns, in general, may contain natural carcinogens and/or the enzyme thiaminase, the latter being dangerous in high concentration. After removing the "brown scales" (sori), leaves were processed likewise. It has gained the Royal Horticultural Society's Award of Garden Merit. Its decomposing fronds make an effective mulch, suppressing undergrowth.