| Abstract from DBPedia | Cycads /ˈsaɪkædz/ are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male or female. Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long. Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group. Cycads are gymnosperms (naked-seeded), meaning their unfertilized seeds are open to the air to be directly fertilized by pollination, as contrasted with angiosperms, which have enclosed seeds with more complex fertilization arrangements. Cycads have very specialized pollinators, usually a specific species of beetle. Both male and female cycads bear cones (strobili), somewhat similar to conifer cones. Cycads have been reported to fix nitrogen in association with various cyanobacteria living in the roots (the "coralloid" roots). These photosynthetic bacteria produce a neurotoxin called BMAA that is found in the seeds of cycads. This neurotoxin may enter a human food chain as the cycad seeds may be eaten directly as a source of flour by humans or by wild or feral animals such as bats, and humans may eat these animals. It is hypothesized that this is a source of some neurological diseases in humans. Other defence mechanisms against herbivores is the accumulation of toxins in seeds and vegetative tissues, and through horizontal gene transfer they have acquired a family of genes from a microbial organism, most likely fungi, which gives them the ability to produce an insecticidal toxin. Cycads all over the world are in decline, with four species on the brink of extinction and seven species having fewer than 100 plants left in the wild. The plant has a very long fossil history, with evidence that they existed in greater abundance and in greater diversity before the Jurassic and late Triassic mass extinction events.ソテツ類（ソテツるい）は、裸子植物の1群である。世界の熱帯、亜熱帯に分布する。ソテツ類は、古生代末から中生代にかけて繁栄した植物で、現生のものは生きている化石と言ってよい。 (Source: http://dbpedia.org/resource/Cycad) |
