Polypodium vulgare
Polypodium vulgare, the common polypody, is an evergreen fern of the family Polypodiaceae. "Polypodium vulgare" is an allotetraploid species, believed to have arisen by chromosome doubling of a sterile diploid hybrid between two ferns which are not known in Europe. The fern's proposed parents are the northern Asian and northern North American "Polypodium sibiricum" and western North American "Polypodium glycyrrhiza". Biochemical data point to a species from eastern Asia as the second possible parent. The name is derived from poly (many) and pous, podos (a foot). Polypody has traditional uses in cooking for its aroma and sweet  taste, and in herbal medicine as a purgative and vermifuge. Description. "Polypodium vulgare", the common polypody, is a fern developing in isolation from along a horizontal rhizome. The fronds with triangular leaflets measure . They are divided all the way back to the central stem in 10 to 18 pairs of segments or leaflets. The leaflets become much shorter at the end of the frond. The leaflets are generally whole or slightly denticulated and somewhat wider at their base, where they often touch each other. They have an alternating arrangement, those on one side being slightly offset from those on the  other side. The petioles have no scales. The sori are found on the lower side of the fronds and range in colour from bright yellow to orange. They became dark grey at maturity. Geographical distribution. The common polypody occurs throughout western Europe and North Africa. It is very common in France, where it is found up to an altitude of . It is also quite common in Scandinavia and Carpathian Mountains. It is an introduced species in New Zealand, that has begun to spread into the wild as an invasive species. Habitat. This fern is found in shaded and semi-shaded  locations. It is a lithophyte (grows on rocks), and is found growing in the moss on old walls, cliffs, cracks in rocks, and in rocky undergrowth; also as an epiphyte on mossy trees. Uses. Research. "P. vulgare" plays the primary role in understanding of plant stomata responses to humidity. The Otto Lange group at the University of Würzburg first showed that stomatal opening and closing was performed in response to environmental humidity with Lange et al 1971, and continued to use it to further illuminate stomatal-humidity responses in stomata-humidty-temperature dynamics in Lösch 1977 & 1979, and metabolic energy  supply to fuel stomatal articulation in Lösch & Tenhunen 1981.