Cycads /ˈsaɪkædz/ are seed plants with a long fossil history that were formerly more abundant and more diverse than they are today. They typically have a stout and woody (ligneous) trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female (dioecious). Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long, with some specimens known to be as much as 1,000 years old. 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. They 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.
|Cycas rumphii with old and new male strobili.|
Bessey 1907: 321.
Cycads have a cylindrical trunk which usually does not branch. Leaves grow directly from the trunk, and typically fall when older, leaving a crown of leaves at the top. The leaves grow in a rosette form, with new foliage emerging from the top and center of the crown. The trunk may be buried, so the leaves appear to be emerging from the ground, so the plant appears to be a basal rosette. The leaves are generally large in proportion to the trunk size, and sometimes even larger than the trunk.
The leaves are pinnate (in the form of bird feathers, pinnae), with a central leaf stalk from which parallel "ribs" emerge from each side of the stalk, perpendicular to it. The leaves are typically either compound (the leaf stalk has leaflets emerging from it as "ribs"), or have edges (margins) so deeply cut (incised) so as to appear compound. Some species have leaves that are bipinnate, which means the leaflets each have their own subleaflets, growing in the same form on the leaflet as the leaflets grow on the stalk of the leaf (self-similar geometry).
Due to superficial similarities in foliage and plant structure between cycads and palms they are often confused with each other. In reality, they belong to completely different phyla, and are not closely related at all. The similar structure may be evidence of convergent evolution.
Despite this, there are still a number of differences between them. For one, both male and female cycads bear a cone-like reproductive structure called a strobilus, while palms are angiosperms and so flower and bear fruit. The mature foliage looks very similar between both groups, but the young emerging leaves of a cycad resemble a fiddlehead fern before they unfold and take their place in the rosette, while the leaves of palms are never coiled up and instead are just small versions of the mature frond. Another difference is in the stem. Both plants leave scars on the stem below the rosette where there used to be leaves, but the scars of a cycad are helically arranged and small, while the scars of palms are a circle that wraps around the whole stem. The stems of cycads are also in general rougher and shorter than those of palms.
The three extant families of cycads all belong to the order Cycadales, and are Cycadaceae, Stangeriaceae, and Zamiaceae. These cycads have changed little since the Jurassic, compared to some major evolutionary changes in other plant divisions. Five additional families belonging to the Medullosales became extinct by the end of the Paleozoic Era.
Cycads have been traditionally put as closely related to the extinct Bennettitales, however recent findings show marked differences In reproductive biology and general anatomy putting doubt on the traditional view. As of yet the evidence points to a pteridospermalean origin of cycads and to a close relation to the Ginkgoales, as shown in the following phylogeny:
|Traditional view||Modern view|
Classification of the Cycadophyta to the rank of family.
Relationships between the extant genera, according to Nagalingum et al. (2011):
Ginkgo, conifers, and gnetophytes
The probable former range of cycads can be inferred from their global distribution. For example, the family Stangeriaceae only contains three extant species in Africa and Australia. Diverse fossils of this family have been dated to 135 mya, indicating that diversity may have been much greater before the Jurassic and late Triassic mass extinction events. However, the cycad fossil record is generally poor and little can be deduced about the effects of each mass extinction event on their diversity.
Instead, correlations can be made between the number of extant gymnosperms and angiosperms. It is likely that cycad diversity was affected more by the great angiosperm radiation in the mid-Cretaceous than by extinctions. Very slow cambial growth was first used to define cycads, and because of this characteristic the group could not compete with the rapidly growing, relatively short-lived angiosperms, which now number over 250,000 species, compared to the 1080 remaining gymnosperms. It is surprising that the cycads are still extant, having been faced with extreme competition and five major extinctions. The ability of cycads to survive in relatively dry environments, where plant diversity is generally lower, may explain their long persistence and longevity.
The cycad fossil record dates to the early Permian, 280 million years ago (mya). There is controversy over older cycad fossils that date to the late Carboniferous period, 300–325 mya. This clade probably diversified extensively within its first few million years, although the extent to which it radiated is unknown because relatively few fossil specimens have been found. The regions to which cycads are restricted probably indicate their former distribution in the Pangea before the supercontinents Laurasia and Gondwana separated. Recent studies have indicated the common perception of existing cycad species as living fossils is largely misplaced, with only Bowenia dating to the Cretaceous or earlier. Although the cycad lineage itself is ancient, most extant species have evolved in the last 12 million years.
The family Stangeriaceae (named for Dr. William Stanger, 1811–1854), consisting of only three extant species, is thought to be of Gondwanan origin, as fossils have been found in Lower Cretaceous deposits in Argentina, dating to 70–135 mya. The family Zamiaceae is more diverse, with a fossil record extending from the middle Triassic to the Eocene (54–200 mya) in North and South America, Europe, Australia, and Antarctica, implying the family was present before the break-up of Pangea. The family Cycadaceae is thought to be an early offshoot from other cycads, with fossils from Eocene deposits (38–54 mya) in Japan, China, and North America, indicating this family originated in Laurasia. Cycas is the only genus in the family and contains 99 species, the most of any cycad genus. Molecular data have recently shown Cycas species in Australasia and the east coast of Africa are recent arrivals, suggesting adaptive radiation may have occurred. The current distribution of cycads may be due to radiations from a few ancestral types sequestered on Laurasia and Gondwana, or could be explained by genetic drift following the separation of already evolved genera. Both explanations account for the strict endemism across present continental lines.
The living cycads are found across much of the subtropical and tropical parts of the world. The greatest diversity occurs in South and Central America. They are also found in Mexico, the Antilles, southeastern United States, Australia, Melanesia, Micronesia, Japan, China, Southeast Asia, India, Sri Lanka, Madagascar, and southern and tropical Africa, where at least 65 species occur. Some can survive in harsh desert or semi-desert climates (xerophytic), others in wet rain forest conditions, and some in both. Some can grow in sand or even on rock, some in oxygen-poor, swampy, bog-like soils rich in organic material. Some are able to grow in full sun, some in full shade, and some in both. Some are salt tolerant (halophytes).
Species diversity of the extant cycads peaks at 17˚ 15"N and 28˚ 12"S, with a minor peak at the equator. There is therefore not a latitudinal diversity gradient towards the equator but towards the Tropic of Cancer and the Tropic of Capricorn. However, the peak near the northern tropic is largely due to Cycas in Asia and Zamia in the New World, whereas the peak near the southern tropic is due to Cycas again, and also to the diverse genus Encephalartos in southern and central Africa, and Macrozamia in Australia. Thus, the distribution pattern of cycad species with latitude appears to be an artifact of the geographical isolation of the remaining cycad genera and their species, and perhaps because they are partly xerophytic rather than simply tropical. Notes: The distribution area on the map should be expanded to include the range of Macrozamia macdonnelliana in the central region of Australia, Zamia boliviana in Bolivia and Mato Grosso, Brazil, Cycas thouarsii on Comoros and Seychelles, and Cycas micronesica on the islands of Guam, Palau, Rota, & Yap. Also, the depiction of cycad distribution in Africa, particularly the western boundary, should be improved to show the actual range limits, rather than national borders.
In Vanuatu, the cycad is known as namele and is an important symbol of traditional culture. It serves as a powerful taboo sign, and a pair of namele leaves appears on the national flag and coat of arms. Together with the nanggaria plant, another symbol of Vanuatu culture, the namele also gives its name to Nagriamel, an indigenous political movement.
Aulacaspis yasumatsui, or cycad aulacaspis scale (CAS), is a scale insect species in the genus Aulacaspis that feeds on cycad species such as Cycas revoluta or Dioon purpusii (Purpus' cycad). Other common names include the cycad scale, the sago palm scale, and the Asian cycad scale. This is a serious pest of cycads which can kill its host plant.Belidae
Belidae is a family of weevils, called belids or primitive weevils because they have straight antennae, unlike the "true weevils" or Curculionidae which have elbowed antennae. They are sometimes known as "cycad weevils", but this properly refers to a few species from the genera Parallocorynus and Rhopalotria.Cycadales
Cycadales is an order of seed plants that includes all the extant cycads. These plants typically have a stout and woody (ligneous) trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female (dioecious). Cycads vary in size from having trunks only a few centimeters to several meters tall. They typically grow very slowly and live very long, with some specimens known to be as much as 1,000 years old. Because of the superficial resemblance, they are sometimes confused with and mistaken for palms or ferns, but are only distantly related to either.
Cycadales are found across much of the subtropical and tropical parts of the world. They are found in South and Central America (where the greatest diversity occurs), Mexico, the Antilles, southeastern United States, Australia, Melanesia, Micronesia, Japan, China, Southeast Asia, India, Sri Lanka, Madagascar, and southern and tropical Africa, where at least 65 species occur. Some can survive in harsh semidesert climates (xerophytic), others in wet rain forest conditions, and some in both. Some can grow in sand or even on rock, some in oxygen-poor, swampy, bog-like soils rich in organic material, and some in both. Some are able to grow in full sun, some in full shade, and some in both. Some are salt tolerant (halophytes).
Cycadales belong to the biological division Cycadophyta along with the fossil order Medullosales. The three extant families of cycadales are Cycadaceae, Stangeriaceae, and Zamiaceae. Though they are a minor component of the plant kingdom today, during the Jurassic period, they were extremely common. They have changed little since the Jurassic, compared to some major evolutionary changes in other plant divisions.
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. They have been reported to fix nitrogen in association with a cyanobacterium living in the roots. These blue-green algae 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.Cycas
Cycas is the type genus and the only genus recognised in the family Cycadaceae. About 113 species are accepted. Cycas circinalis, a species endemic to India was the first cycad species to be described and was the type of the generic name, Cycas. The best-known Cycas species is Cycas revoluta. Cycas is a very ancient genus of trees. The group achieved its maximum diversity in the Jurassic and Cretaceous periods, when it was distributed almost worldwide. At the end of the Cretaceous, when the non-avian dinosaurs became extinct, so did most of the cycas in the Northern Hemisphere.Cycas beddomei
Cycas beddomei is a species of cycad in the genus Cycas, native to India, where it is confined to a small area of Andhra Pradesh state in the Tirumala Hills in scrubland and brush covered hills.
Superficially similar to Cycas revoluta, it has erect, solitary stems. There are 20-30 leaves in the crown, each leaf 90 cm long, stiff, lanceolate, pinnate, with 50-100 pairs of leaflets, these 10-17.5 cm long and 3–4 mm wide, and angled forward at 45 degrees; the leaf petiole bears minute spines.
The female cones are open, with sporophylls 15–20 cm long, with pink-brown coloured tomentose down, with two ovules. The cones emerge in November to December, ripening in March to May. The lamina margin is strongly toothed, with an acuminate point. The sarcotesta is yellow to brown. The male cones are solitary, ovoid, 30 cm long and 7.5 cm broad, with an apical spine and rhomboid sporophyll face.
The species is unusual in that it contains a layer of fleshy material between the sarcotesta and the sclerotesta that is thought to aid the seed by providing it with a source of water. As cycad seeds have no dormancy, this would be an important trait in its arid habitat.
It is named after the botanist Richard Henry Beddome.Cycas circinalis
Cycas circinalis, also known as the queen sago, is a species of cycad known in the wild only from southern India. Cycas circinalis is the only gymnosperm species found among native Sri Lankan flora.Cycas revoluta
Cycas revoluta (Sotetsu [Japanese ソテツ], sago palm, king sago, sago cycad, Japanese sago palm), is a species of gymnosperm in the family Cycadaceae, native to southern Japan including the Ryukyu Islands. It is one of several species used for the production of sago, as well as an ornamental plant.Dioon purpusii
Dioon purpusii (Purpus' cycad) is a cycad tree endemic to a very small region in Mexico (Oaxaca, Puebla). It is found in Tomellín Canyon and the eastern branches of La Cañada de Cuicatlán.Encephalartos altensteinii
Encephalartos altensteinii is a palm-like cycad in the family Zamiaceae. It is endemic to South Africa. The species name altensteinii commemorates Altenstein, a 19th-century German chancellor and patron of science. It is commonly known as the breadtree, broodboom, eastern Cape giant cycad or uJobane (Zulu). It is listed as vulnerable due to habitat destruction, use for traditional medicine and removal by collectors.Encephalartos lehmannii
Encephalartos lehmannii is a low-growing palm-like cycad in the family Zamiaceae. It is commonly known as the Karoo cycad and is endemic to South Africa. The species name lehmannii commemorates Prof J.G.C. Lehmann, a German botanist who studied the cycads and published a book on them in 1834. This cycad is listed as near threatened in the IUCN Red List of Threatened Species.Fossil Cycad National Monument
Fossil Cycad National Monument was a national monument in the U.S. state of South Dakota beginning in 1922. The site contained hundreds of fossil cycads, one of the world's greatest concentrations. Because vandals stole or destroyed all of the visible fossils, it was withdrawn as a national monument in 1957. It is located in northwestern Fall River County, on U.S. Route 18, northeast of the city of Edgemont.Luthrodes pandava
Luthrodes pandava (formerly Chilades pandava), the plains Cupid or cycad blue, is a species of lycaenid butterfly found in India, Sri Lanka, Myanmar, United Arab Emirates, Indochina, Peninsular Malaysia, Singapore, Taiwan, Java, Sumatra and the Philippines. They are among the few butterflies that breed on plants of the cycad class.Palm and Cycad Arboretum
The Palm and Cycad Arboretum at the Florida State College at Jacksonville is located on the south campus at 11901 Beach Boulevard, Jacksonville, Florida, United States. This is an outdoor area next to the G building, a large three-story complex in the middle of campus that houses the library and other facilities. There is also a biologically diverse area of larger trees and mid-growth brush in an immediate westerly direction to this area. As the Arboretum is an open area, there are no specific set hours, and its use is free and available to all students and visitors.
Collections include Acoelorrhaphe wrightii, Allagoptera arenaria, Arenga engleri, Braea armataz, Brahea brandegeei, Chamaedorea microspadix, Chamaedorea radicalis, Chamaerops humil, Cycas revoluta, Dioon edule, Dioon spinolusum, Livistona drudei, Livistona mariae, Livistona speciosa, Phoenix reclinata, Phoenix theophrasti, Sabal mauritiiformis, Trithrinax acanthocoma, and Zamia pumila.Sago
Sago is a starch extracted from the spongy centre, or pith, of various tropical palm stems, especially that of Metroxylon sagu. It is a major staple food for the lowland peoples of New Guinea and the Moluccas, where it is called saksak, rabia and sagu. The largest supply of sago comes from Southeast Asia, particularly Indonesia and Malaysia. Large quantities of sago are sent to Europe and North America for cooking purposes. It is traditionally cooked and eaten in various forms, such as rolled into balls, mixed with boiling water to form a glue-like paste (papeda), or as a pancake. Sago is often produced commercially in the form of "pearls" (small rounded starch aggregates, partly gelatinized by heating). Sago pearls can be boiled with water or milk and sugar to make a sweet sago pudding. Sago pearls are similar in appearance to the pearled starches of other origin, e.g. cassava starch (tapioca) and potato starch, and they may be used interchangeably in some dishes.
The name sago is also sometimes used for starch extracted from other sources, especially the sago cycad, Cycas revoluta. The sago cycad is also commonly known (confusingly) as the sago palm, although this is a misnomer as cycads are not palms. Extracting edible starch from the sago cycad requires special care due to the poisonous nature of cycads. Cycad sago is used for many of the same purposes as palm sago.
The fruit of palm trees from which the sago is produced is not allowed to ripen fully. The full ripening completes the life cycle of the tree and exhausts the starch reserves in the trunk to produce the seeds. It leaves a hollow shell and causes the tree to die. The palms are cut down when they are about 15 years old, just before or shortly after the inflorescence appears. The stems, which grow 10 to 15 metres high), are split out. The starch-containing pith is taken from the stems and ground to powder. The powder is kneaded in water over a cloth or sieve to release the starch. The water with the starch passes into a trough where the starch settles. After a few washings, the starch is ready to be used in cooking. A single palm yields about 800 pounds (360 kilograms) of dry starch.Sago palm
Sago palm is a common name for several plants which are used to produce a starchy food known as sago. Sago palms may be "true palms" in the family Arecaceae, or cycads with a palm-like appearance. Sago produced from cycads must be detoxified before consumption. Plants called sago palm include:
Metroxylon sagu (true sago palm), a species in the palm family (Arecaceae) native to Southeast Asia
Cycas revoluta, (king sago palm), native to Japan and widely cultivated as an ornamental plant
Cycas rumphii, (queen sago palm), native to southeast Asia
Cycas circinalis, (queen sago palm), native to IndiaSarcotesta
The sarcotesta is a fleshy seedcoat, a type of testa. Examples of seeds with a sarcotesta are pomegranate and some cycad seeds. The sarcotesta of pomegranate seeds consists of epidermal cells derived from the integument, and there are no arils on these seeds.Zamia
Zamia is a genus of cycad of the family Zamiaceae, native to Mexico, the West Indies, and Central and South America as far south as Bolivia. The range of one species (Z. integrifolia, extends into the contiguous United States, i.e. Georgia and Florida.
The genus comprises deciduous shrubs with aerial or subterranean circular stems, often superficially resembling palms. They produce spirally arranged, pinnate leaves which are pubescent, at least when young, having branched and simple, transparent and coloured hairs. The articulated leaflets lack a midrib, and are broad with subparallel dichotomous venation. Lower leaflets are not reduced to spines, though the petioles often have prickles. The emerging leaves of many Zamia species are striking, some emerging with a reddish or bronze cast (Z. roesli is an example). Zamia picta is even more distinctive, being the only truly variegated cycad (having whitish/yellow speckles on the leaves).Zamia sporophylls are born in vertical rows in cones, and the megasporophyll apices are faceted or flattened, not spinose. The fleshy seeds are subglobular to oblong or ellipsoidal, and are red, orange, yellow or rarely white. The endosperm is haploid, derived from the female gametophyte. The embryo is straight, with two cotyledons that are usually united at the tips and a very long, spirally twisted suspensor.
The sperm of the genus are large, as is typical of cycads, and Zamia roezlii is an example; its sperm are approximately 0.4 mm long and can be seen by the unaided eye.All the species of Zamia produce leafy crowns of foliage that make them choice garden specimens and most varieties branch heavily in age to produce handsome clumps. With a few exceptions, most Zamia species are found in warm, humid, tropical rainforest habitats, growing in the forest understory. However, many species are still fairly adaptable, performing quite well in cultivation, especially in subtropical areas. All species need good drainage and protection from the cold.
At least one species, Z. pseudoparasitica, grows as an epiphyte in the branches of trees.
The name Zamia comes from the Greek azaniae, meaning "a pine cone".Zamia furfuracea
Zamia furfuracea is a cycad native to southeastern Veracruz state in eastern Mexico. Although not a palm tree (Arecaceae), its growth habit is superficially similar to a palm; therefore it is commonly known as cardboard palm or cardboard cycad. Other names include cardboard plant, cardboard sago, Jamaican sago, and Mexican cycad (from Mexican Spanish Cícada Mexicana). The plant's binomial name comes from the Latin zamia, for "pine nut", and furfuracea, meaning "mealy" or "scurfy".Zamites
Zamites is a genus of fossil tree known from the Mesozoic of North America, Europe and India through the Eocene of North America. It is a form taxon for leaves that resemble the extant cycad Zamia. The fronds are linear or lanceolate in shape, and pinnately compound, with pinnae with parallel veins and smooth margins, and symmetrical and constricted at the base where they are attached obliquely to the upper surface of the rachis. It has been interpreted as a cycad in the family Cycadaceae or a Bennettitalean plant.
& land plants)
|True, or botanical nuts|
Extant Life phyla/divisions by domain