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Cycads are
seed plant A spermatophyte (; ), also known as phanerogam (taxon Phanerogamae) or phaenogam (taxon Phaenogamae), is any plant that produces seeds, hence the alternative name seed plant. Spermatophytes are a subset of the embryophytes or land plants. They inc ...

seed plant
s that typically have a stout and woody ( ligneous) trunk with a crown of large, hard, stiff,
evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, ...

evergreen
and (usually)
pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common Anatomical terms of location#Axes, axis. Pinnation occurs in biological morphology (biology), morphology, in Crysta ...
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
palms
or
fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The Polypodiophyta, polypodiophytes include all living pteridop ...

fern
s, but they are not closely related to either group. Cycads are gymnosperms (naked-seeded), meaning their
unfertilized
unfertilized
seeds are open to the air to be directly fertilized by
pollination Pollination is the transfer of pollen from an Stamen, anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by Anemophily, wind. Pollinating agents can ...

pollination
, as contrasted with angiosperms, which have enclosed seeds with more complex fertilization arrangements. Cycads have very specialized
pollinator A pollinator is an animal that moves pollen from the male anther of a flower to the female carpel, stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insects are ...

pollinator
s, usually a specific species of
beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, Elytron, elytra, distinguishing them from most other insects. The Coleoptera, wit ...

beetle
. Both male and female cycads bear cones ( strobili), somewhat similar to
conifer cone A conifer cone (in formal botany, botanical usage: strobilus, plural strobili) is a seed-bearing organ on gymnosperm plants. It is usually woody, ovoid to globular, including scales and bracts arranged around a central axis, especially in con ...
s. Cycads have been reported to fix nitrogen in association with various
cyanobacteria
cyanobacteria
living in the roots (the "coralloid" roots). These photosynthetic bacteria produce a neurotoxin called BMAA that is found in the
seed
seed
s 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.


Description

Cycads have a cylindrical trunk which usually does not
branch
branch
. However, some types of cycads, such as ''Cycas zeylanica,'' can branch their trunks. The apex of the stem is protected by modified leaves called cataphylls. 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 Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common Anatomical terms of location#Axes, axis. Pinnation occurs in biological morphology (biology), morphology, in Crysta ...
(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. The Australian genus Bowenia and some Asian species of Cycas, like Cycas multipinnata,
Cycas micholitzii
Cycas micholitzii
and Cycas debaoensis, have leaves that are
bipinnate The following is a list of terms which are used to describe leaf plant morphology, morphology in the description and taxonomy (biology), taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflet (bo ...
, 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
self-similar geometry
).


Confusion with palms

Due to superficial similarities in foliage and plant structure, cycads and
palms
palms
are often mistaken for each other. They also can occur in similar climates. However, they belong to different phyla and as such are not closely related. The similar structure is the product of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
. Beyond those superficial resemblances, there are a number of differences between cycads and palms. For one, both male and female cycads are
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...
s and bear cones (strobili), while palms are
angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek language, Greek words ('container, vessel') and ('seed'), and refers to ...
s 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 Fiddleheads or fiddlehead greens are the furled fronds of a young fern, harvested for use as a vegetable. Left on the plant, each fiddlehead would unroll into a new frond (circinate vernation). As fiddleheads are harvested early in the sea ...
before they unfold and take their place in the rosette, while the leaves of palms are just small versions of the mature frond. Another difference is in the
stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...
. Both plants leave some 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.


Taxonomy

The two extant
families Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
of cycads all belong to the order Cycadales, and are the
Cycadaceae ''Cycas'' is a genus of plants belonging to a very ancient lineage, the Cycadophyta, which are not closely related to palms, ferns, trees or any other modern group of plants. They are evergreen perennial plant, perennials which achieved their maxi ...
and
Zamiaceae The Zamiaceae are a family of cycads that are superficially palm or fern-like. They are divided into two subfamilies with eight genera and about 150 species in the tropical and subtropical regions of Africa, Australia and North America, North and ...
(including Stangeriaceae). These cycads have changed little since the Jurassic in comparison to some other plant divisions. Five additional families belonging to the
Medullosales The Medullosales is an extinct order of pteridospermous seed plants characterised by large ovules with circular cross-section and a vascularised nucellus In seed plants, the ovule is the structure that gives rise to and contains the femal ...
became extinct by the end of the Paleozoic Era. Based on genetic studies, cycads are thought to be more closely related to ''
Ginkgo ''Ginkgo'' is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and is now the only living genus within t ...
'' than other living gymnosperms. Both are thought to have diverged from each other during the early
Carboniferous The Carboniferous ( ) is a Period (geology), geologic period and System (stratigraphy), system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago (Myr, Mya), to the beginning of the Permian Period, ...
. Classification of the Cycadophyta to the rank of family. * Class Cycadopsida Brongniart 1843 ** Order Cycadales Persoon ex von Berchtold & Presl 1820 *** Suborder Cycadineae Stevenson 1992 **** Family
Cycadaceae ''Cycas'' is a genus of plants belonging to a very ancient lineage, the Cycadophyta, which are not closely related to palms, ferns, trees or any other modern group of plants. They are evergreen perennial plant, perennials which achieved their maxi ...
Persoon 1807 ***** Genus ''
Cycas ''Cycas'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological cl ...
'' *** Suborder Zamiineae Stevenson 1992 **** Family
Zamiaceae The Zamiaceae are a family of cycads that are superficially palm or fern-like. They are divided into two subfamilies with eight genera and about 150 species in the tropical and subtropical regions of Africa, Australia and North America, North and ...
Horaninow 1834 ***** subfamily Diooideae Pilg. 1926 ****** Genus '' Dioon'' ***** subfamily Zamioideae Stevenson 1992 ****** Tribe Encephalarteae Miquel 1861 ******* Genus '' Macrozamia'' ******* Genus '' Lepidozamia'' ******* Genus ''
Encephalartos ''Encephalartos'' is a genus of cycad native to Africa. Several species of ''Encephalartos'' are commonly referred to as bread trees, bread palms or kaffir bread, since a bread-like starchy food can be prepared from the centre of the stem. The ge ...
'' ****** Tribe Zamieae Miquel 1861 ******* Genus '' Bowenia'' ******* Genus '' Ceratozamia'' ******* Genus '' Stangeria'' ******* Genus '' Zamia'' ******* Genus '' Microcycas''


Fossil record

The probable former range of cycads can be inferred from their global distribution. For example, the family Stangeriaceae contains only 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 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.


Origins

The cycad fossil record dates to the early
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...
, ( mya). There is controversy over older cycad fossils that date to the late
Carboniferous The Carboniferous ( ) is a Period (geology), geologic period and System (stratigraphy), system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago (Myr, Mya), to the beginning of the Permian Period, ...
period, . This
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants – on a phylogenetic tree. ...
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
Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia (continent), Siberia during the Carboniferous approx ...
supercontinent before the supercontinents
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around (Mya (unit), Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the bre ...
and
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic, Jurassic period (about 180 million years ago). The fi ...
separated. Recent studies have indicated that the common perception of existing cycad species as
living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living fossi ...
s is largely misplaced, with only '' Bowenia'' dating to the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 79 million years, it is the long ...
or earlier. Although the cycad lineage itself is ancient, most extant species have evolved in the last 12 million years. Although the Mesozoic is sometimes called the "Age of Cycads," the foliage of cycads is very similar to other groups of extinct seed plants, such as
Bennettitales Bennettitales (also known as cycadeoids) is an extinct order of seed plants that first appeared in the Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of ...
and Nilssoniales, that are not closely related, and cycads were probably only a minor component of mid-Mesozoic floras. The
family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Stangeriaceae (named for Dr. William Stanger, 1811–1854), consisting of only three
extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
, is thought to be of Gondwanan origin, as fossils have been found in
Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Gloucestershire, England See also

*Nizhny {{Disambiguation ...
deposits in
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the List of South American countries by area, second-largest ...
, dating to . The family
Zamiaceae The Zamiaceae are a family of cycads that are superficially palm or fern-like. They are divided into two subfamilies with eight genera and about 150 species in the tropical and subtropical regions of Africa, Australia and North America, North and ...
is more diverse, with a fossil record extending from the middle
Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
to the
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek Anci ...
() in
North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...
and South America,
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, Australia, and
Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar regions of Earth, polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kergu ...
a, implying the family was present before the break-up of Pangea. The family
Cycadaceae ''Cycas'' is a genus of plants belonging to a very ancient lineage, the Cycadophyta, which are not closely related to palms, ferns, trees or any other modern group of plants. They are evergreen perennial plant, perennials which achieved their maxi ...
is thought to be an early offshoot from other cycads, with fossils from
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek Anci ...
deposits () in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, and
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, indicating this family originated in Laurasia. ''
Cycas ''Cycas'' is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological cl ...
'' is the only
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
in the family and contains 99 species, the most of any cycad genus.
Molecular A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
data have recently shown ''Cycas'' species in
Australasia Australasia is a region that comprises Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. ...
and the east coast of Africa are recent arrivals, suggesting
adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...
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 Genetic drift, also known as allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear co ...
following the separation of already evolved genera. Both explanations account for the strict
endemism Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are Indigenous (ecology), indigenous to a place are not endemic to it if the ...
across present continental lines.


Distribution

The living cycads are found across much of the
subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...
and
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
parts of the world. The greatest diversity occurs in
South South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...
and
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. Cen ...
. They are also found in
Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
, the
Antilles The Antilles (; gcf, label=Antillean Creole, Antiy; es, Antillas; french: Antilles; nl, Antillen; ht, Antiy; pap, Antias; Jamaican Patois: ''Antiliiz'') is an archipelago bordered by the Caribbean Sea to the south and west, the Gulf of Mex ...
, southeastern
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
,
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
,
Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from Indonesia's Western New Guinea, New Guinea in the west to Fiji in the east, and includes the Arafura Sea. The region includes the four independent cou ...
,
Micronesia Micronesia (, ) is a subregion of Oceania, consisting of about 2,000 small islands in the western Pacific Ocean. It has a close shared cultural history with three other island regions: the Philippines to the west, Polynesia to the east, and ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...
,
Bangladesh Bangladesh (}, ), officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world, with a population exceeding 165 million pe ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
,
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
,
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
, and southern and tropical
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, where at least 65
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
occur. Some can survive in harsh
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one ...
or semi-desert
climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologi ...
s (
xerophytic A xerophyte (from Ancient Greek language, Greek ξηρός ''xeros'' 'dry' + φυτόν ''phuton'' 'plant') is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or pl ...
), others in wet
rain forest Rainforests are characterized by a closed and continuous tree Canopy (biology), canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or tem ...
conditions, and some in both. Some can grow in
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...
or even on rock, some in oxygen-poor, swampy,
bog A bog or bogland is a wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (Anoxic waters, anoxic) ...
-like soils rich in
organic material Organic matter, organic material, or natural organic matter refers to the large source of Carbon compounds, carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic comp ...
. Some are able to grow in full sun, some in full shade, and some in both. Some are
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in the form of a natural crystallinity, crystalline mineral is known as rock salt or halite. ...
tolerant (
halophyte A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores. Th ...
s). Species diversity of the extant cycads peaks at 17˚ 15"N and 28˚ 12"S, with a minor peak at the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the ...
. There is therefore not a latitudinal diversity gradient towards the equator but towards the
Tropic of Cancer The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be subsolar point, directly overhead. This occurs on the June solstice, when the Northern Hemisphere i ...
and the
Tropic of Capricorn The Tropic of Capricorn (or the Southern Tropic) is the circle of latitude that contains the subsolar point at the December (or southern) solstice. It is thus the southernmost latitude where the Sun can be seen directly overhead. It also reach ...
. 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 A xerophyte (from Ancient Greek language, Greek ξηρός ''xeros'' 'dry' + φυτόν ''phuton'' 'plant') is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or pl ...
rather than simply
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
.


Cultural significance

In
Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (french: link=no, République de Vanuatu; bi, Ripablik blong Vanuatu), is an island country located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of no ...
, the cycad is known as ''namele'' and is an important symbol of traditional culture. It serves as a powerful
taboo A taboo or tabu is a social group's ban, prohibition, or avoidance of something (usually an utterance or behavior) based on the group's sense that it is excessively repulsive, sacred, or allowed only for certain persons.''Encyclopædia Britannica ...
sign, and a pair of ''namele'' leaves appears on the
national flag A national flag is a flag that represents and symbolizes a given nation. It is Fly (flag), flown by the government of that nation, but usually can also be flown by its citizens. A national flag is typically designed with specific meanings for it ...
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.


See also

* Fossil Cycad National Monument, formerly in the U.S. state of South Dakota


Footnotes


References


External links


Palm Trees, Small Palms, Cycads, Bromeliads and tropical plants
site with thousands of large, high quality photos of cycads and associated flora. Includes information on habitat and cultivation. *Hill KD (1998–2004) The Cycad Pages, Royal Botanic Gardens Sydney. http://plantnet.rbgsyd.nsw.gov.au/PlantNet/cycad/index.html



* ttp://www.pacsoa.org.au/ Palm and Cycad Societies of Australia (PACSOA)
The Cycad Society of South Africa






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The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid d ...
'' Magazine article on cycad collectorship and cycad smuggling {{Taxonbar, from1=Q1089795, from2=Q157114, from3=Q5197912, from4=Q5605610 Dioecious plants Cisuralian first appearances Extant Permian first appearances