Ecology and distribution
Disturbances alter the population dynamics of Dioon edule populations. If a population is heavily dominated by adult plants, the disturbance will be minimal as compared to the population consisting of younger plants. This is due to their ability to survive harsh conditions. D. edule exemplifies a Type III survivorship curve and clumped distributions. It is found mostly on shallow, rocky soils due to competition with other, faster growing species for water, nutrients and seed dispersal. In response, they have developed a selective advantage for growing in these harsh climates including vigorous tap roots for anchorage and water conduction. Furthermore, it is harder for rodents to reach the plant and seeds if they are established in difficult locations to reach. In addition to competition, causal agents of D. edule's random, clumped distribution include predation, variations in temperature and precipitation, and measures of seed dispersal.
Death rates among seedlings are considerable, which is detrimental to a slow-growing plant such as the Dioon edule. Seeds must combat harsh, dry climates and frequent bushfires. Most mature plants are heavily armored and able to withstand these fires. Smaller seeds and juvenile plants are not so fortunate. However, the release of nutrients and minerals encourages females to develop cones during the following season. In addition to climate, seeds must also avert rodent predators. This is reasonably unusual because cycad seeds and foliage are poisonous to most mammals, excluding these varied species of rodents. Young leaves of D. edule are also eaten by the Eumaeus debora butterfly larvae.
One of the ways in which cycads are identified includes leaflet characteristics, which were not heavily studied when cycads were first identified. In subsequent studies it was found that leaflet width was related to geographic dispersal. Wider leaves typical of Dioon edule subsp. edule are found in the south whereas the narrower leaves of D. edule subsp. angustifolium are found to the north. Evidence suggests D. edule subsp. edule was much more widespread than it is today and became fragmented thus allowing for genetic isolation. It is also speculated that the narrower leaves are endemic in the northern subspecies due to less temperate and humid environmental conditions in these areas.
In addition, endomycorrhizae are present in roots and allow for increased absorption of nutrients and water. Symbiotic blue-green algae are also found in the coralloid (i.e. upward growing) roots. They assist the plant by fixing nitrogen thus giving the plant essential nutrients in exchange for protection. Cycads in general have significant roles in the nitrogen budget of their respective ecosystems.
Cycads 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 slowly and have long lifespans. Because of their superficial resemblance to palms or ferns, they are sometimes mistaken for them, 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.
Pinus cembroides, also known as pinyon pine, Mexican pinyon, Mexican nut pine, and Mexican stone pine, is a pine in the pinyon pine group, native to western North America. It grows in areas with low levels of rainfall and its range extends southwards from Arizona, Texas and New Mexico in the United States into Mexico. It typically grows at altitudes between 1,600 and 2,400 metres. It is a small pine growing to about 20 m (66 ft) with a trunk diameter of up to 50 cm (20 in). The seeds are large and form part of the diet of the Mexican jay and Abert's squirrel. They are also collected for human consumption, being the most widely used pine nut in Mexico. This is a common pine with a wide range and the International Union for Conservation of Nature has rated its conservation status as being of "least concern".
Cycas is a genus of cycad, and the only genus in the family Cycadaceae with all other genera of cycad being divided between the Stangeriaceae and Zamiaceae families. Cycas circinalis, a species endemic to India, was the first cycad species to be described in western literature, and is the type species of the genus.
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 and South America.
Zamia is a genus of cycad of the family Zamiaceae, native to North America from the United States throughout the West Indies, Central America, and South America as far south as Bolivia. The genus is considered to be the most ecologically and morphologically diverse of the cycads, and is estimated to have originated about 68.3 million years ago.
Dioon is a genus of cycads in the family Zamiaceae. It is native to Mexico and Central America. Their habitats include tropical forests, pine-oak forest, and dry hillsides, canyons and coastal dunes.
A strobilus is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but some botanists restrict the use of the term cone to the woody seed strobili of conifers. Strobili are characterized by a central axis surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.
Banksia nobilis, commonly known as the golden dryandra, great dryandra or kerosene bush, is a shrub of the family Proteaceae which is endemic to Western Australia. It occurs on lateritic rises from Eneabba to Katanning in the state's Southwest Botanic Province. With large pinnatifid leaves with triangular lobes, and a golden or reddish pink inflorescence, it is a popular garden plant. It was known as Dryandra nobilis until 2007, when all Dryandra species were transferred to Banksia by Austin Mast and Kevin Thiele. There are two subspecies, B. nobilis subsp. nobilis and B. nobilis subsp. fragrans.
Ceratozamia morettii is a species of plant in the family Zamiaceae. It is endemic to Mexico, where it is limited to the state of Veracruz north of Jalapa. It grows on steep clay and basalt cliffs in cloud forest habitat.
Ceratozamia sabatoi is a species of plant in the family Zamiaceae. It is endemic to Mexico, where it occurs in the states of Hidalgo and Querétaro. It is known from only two localities, one of which is degraded by agriculture and grazing.
Ceratozamia whitelockiana is a species of plant in the family Zamiaceae. It is endemic to Mexico, where it is known only from Metates and Chiapan in Oaxaca state. Only two subpopulations have been found, with a total population of about 2200 individuals. The habitat is threatened by conversion to plantations using slash-and-burn techniques.
Macrozamia miquelii, is a species of cycad in the plant family Zamiaceae. It is endemic to Queensland and New South Wales in Eastern Australia. Located within sclerophyll forests dominated by eucalyptus trees, the cycad grows on nutrient-poor soils. It is recognised within the Zamiaceae family for its, medium height at 1 m, intermediate size of male and female cones and lighter green leaves compared to other cycads within the plant family of Zamiaceae. The seeds have an orange red sarcotesta which attracts fauna consumption, allowing a mutualistic seed dispersal for the cycad. These seeds are also edible for human consumption if prepared correctly to remove the toxins.
Macrozamia spiralis is a species of cycad in the family Zamiaceae. It is endemic to New South Wales in eastern Australia, where it is found in sclerophyll forest on low-nutrient soils. Plants generally lack a trunk and have 2–12 leaves that range up to 100 cm (40 in) in length.
Zamia fischeri is a species of cycad in the family Zamiaceae. It is endemic to Mexico. It is often confused with Zamia vazquezii. Zamia fischeri is named after Gustav Fischer, a cycad enthusiast of the nineteenth century.
Zamia pseudoparasitica is a species of plant in the family Zamiaceae. It is endemic to Panama.
Dioon purpusii is a cycad tree endemic to a very small region in Mexico. It is found in Tomellín Canyon and the eastern branches of La Cañada de Cuicatlán.
Encephalartos afer, commonly known as the Eastern Cape dwarf cycad, is a species of cycad in the genus Encephalartos. It is a near threatened species native to South Africa.
Dioon tomasellii is a species of cycad in the family Zamiaceae. It is endemic to Mexico, where it occurs in the states of Durango, Guerrero, Jalisco, Michoacán, and Nayarit.
Dioon holmgrenii is a species of cycad in the family Zamiaceae. It is endemic to Mexico, where it occurs only in an area just to the southwest of San Gabriel Mixtepec, Oaxaca. It is known by the common name palma del sol.
Zamia integrifolia, also known as coontie, is a small, tough, woody cycad native to the southeastern United States, the Bahamas, Cuba, the Cayman Islands, and Puerto Rico.
