Diverse habitats of Cycads
Living cycads are found in the tropical, subtropical and warm temperate regions of both the Northern and Southern hemispheres. The region of greatest cycad diversity is Central America. Substantial numbers exist in South Africa, Australia, South America, southern parts of North America and the Caribbean islands.
Cycas is the most widely distributed genus, occurring in Japan and China, Asia, South-East Asia, various islands of the Pacific, Australia and the east coast of Africa and Madagascar.
Cycads growing in the most southerly and northerly extremes can experience heavy frosts, winter rains and even survive being covered by snow for short periods of time as with Encephalartos heenanii in South Africa which grows on Subalpine slopes at around 1500m Altitude, For Cold Hardiness Info have a look at the following link : Peter Hueppi’s CRDB Cold Rating Database.
Cycads are also xerophytic and grow in seasonally dry conditions in the dry subtropics and inland desert regions where they can experience extended dry periods of 8 months or more with no adverse effects as with Macrozamia macdonnellii and other cycas that grow on the near desert fringes of northern Australia in protected Gorges and southern slopes (northern slopes in the northern hemisphere) to escape the burning heat of the sun.
Wet Swampy Tidal Environments
Cycads also grow in swampy environments as in Central America where a Zamia sp grows in and on the verge of mangrove swamps as with Zamia roezlii, Cycads also grow in the near vicinity of the coastlines and experience quite high salt levels when the winds and tidal surges , Hurricanes, Cyclones etc deposit salt into their environment. Zamias in Florida for example are quite regularly exposed to high levels of salt through sea spray and inundation by the extreme Hurricanes and Tornadoes experienced there.
Cycads have even taken to the trees as Epiphytes as in Zamia pseudoparasitica which spends its life high in the crotch of trees in a high rainfall area, the seeds that drop to the ground do not survive for very long in what is an unfavourable, inhospitable environment for them.
Nutrient Deficient/Skeletal Soils
Cycads have the ability to grow in some of the poorest soils in the world as in the North West of Australia where there are the oldest exposed land surface in the world , These soils are extremely low in nutrient levels, Phosphorus especially, these plants as well as the other plants associated with them have developed an extremely efficient way of extracting this nutrient from the soil, when in cultivation these plants can be killed with applications of higher levels of Phosphorus.
Cycads have roots that grow up from the base against the force of gravity and form Coral like structures at or above the soil surface. These are populated by a blue-green nitrogen fixing cyanobacteria that form a symbiotic relationship with the host cycad. These cyanobacteria were not present in these structures when the plant first formed the corraloid roots but were populated some time later in the plants development, the presence of the bacteria can be identified by cutting a nodule of the root , a blue/green line can be seen near the outer layer. Basically these cyanobacteria extract nitrogen from the air and present it to the host plant in return for board and lodgings. This feature allows Cycads to flourish where other plants may struggle to exist in soils with poor nutrient levels.
Insect Pollination of Cycad Cones
Weevils are the pollinators of cycads, they are found to be host specific. These insects live their whole life cycle in and around the plants. Cycads have male and female cones on separate plants, as cones mature, female cones become receptive, male cones dehisc pollen. When the cycad cones mature the cones on the M and F plants elongate by ¼ to 1/3 in length and amazingly increase in temperature up to 4-6 degrees above the ambient air temperature, this has the effect of the odour produced by the mature Cones to rise with the warmer air currents from the cones, thus being distributed by the air movements , the odour is quite strong and unique in scent in most species of cycads, this in turn attracts the pollinators that may be mating in or feeding on pollen of male cone thus becoming covered in pollen, they then transfer it to the receptive female, being attracted by the scent, then brushing the pollen against the receptive ovules in their search for food and a site to lay their eggs thus effecting the pollination cycle.
"Age of the Cycads"
||78 million years
||64 million years
||37 million years
||41 million years
||74 million years
||48 million years
||28 million years
||69 million years
||65 million years
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