Onoclea sensibilis

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, 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. ==Taxonomy==

Taxonomic history Species 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. Varieties Onoclea sensibilis has two geographically disjunctive varieties. Onoclea sensibilis var. sensibilis is native to North America; Canada's central and eastern regions and the United States' north, central and eastern regions. • dwa’hũdes gananitsga’kwaʼ; Cayuga, meaning "deer, what they lie on" • helmisaniainen; Finnish, meaning "mother of pearl" • pärlbräken; Swedish, meaning "pearl bracts" ==Distribution and habitat==

Onoclea sensibilis is native to Northern Hemisphere temperate regions; the Russian Far East, China and Eastern Asia, and a wide native distribution in Northern America. It ranges from Newfoundland south to Florida and west to Texas, the Rocky Mountains, North and South Dakota, Quebec, and Manitoba. It has become naturalized in western Europe and New Zealand. moderately saline water and higher. Onoclea sensibilis grows best in moist shaded or partially shaded areas, dwelling in a variety of swamp and wood habitats: wet meadows, thickets and bogs, as well as stream and riverbanks and roadside ditches. It tolerates extremely wet soils, appearing in soggy ground or at the very edge of water in shade or sun. The plant can tolerate dryer conditions in shade. It prefers acidic (pH <6.8), loose, sandy to loam, limestone-based soils. ==Ecology==

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. Bacteria Onoclea sensibilis can host Burkholderia plantarii ==Toxicity==

Pharmacology 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. Mammal 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. Historically, some Native American peoples have consumed Onoclea sensibilis without apparent distress; see Food uses in this article. ==Uses==

Food Onoclea sensibilis has limited value for food use, 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. ==See also==