Download
1 / 27
E N D
Cycads are seed plants typically characterized by 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 a trunk that is only a few centimeters tall to trunks up 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 confused with and mistaken for palms or ferns, but are only distantly related to either. Cycads 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 semidesertclimates (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). Cycads belong to the biological divisionCycadophyta. There are three extant families of cycads, 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 that their unfertilized seeds (ovules) 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 kind of beetle. They have been reported to fix nitrogen in association with a cyanobacterium living in the roots. These blue-green algae produce aneurotoxin called BMAA that is found in the seeds of cycads. A neurotoxin cycling through the food chain from the cyanobacterium through cycads to its seeds, to bats eating the seeds, to humans consuming the bats, is hypothesized to be a source for some neurological diseases in humans
Description This very symmetrical plant supports a crown of shiny, dark green leaves on a thick shaggy trunk that is typically about 20 cm (7.9 in) in diameter, sometimes wider. The trunk is very low to subterranean in young plants, but lengthens above ground with age. It can grow into very old specimens with 6–7 m (over 20 feet) of trunk; however, the plant is very slow-growing and requires about 50–100 years to achieve this height. Trunks can branch multiple times, thus producing multiple heads of leaves.
The leaves are a deep semiglossy green and about 50–150 cm (20–59 in) long when the plants are of a reproductive age. They grow out into a feather-like rosette to 1 m (3.3 ft) in diameter. The crowded, stiff, narrow leaflets are 8–18 cm (3.1–7.1 in) long and have strongly recurved or revolute edges. The basal leaflets become more like spines. The petiole or stems of the Sago Cycad are 6–10 cm (2.4–3.9 in) long and have small protective barbs that must be avoided. Propagation of Cycas revoluta is either by seed or by removal of basal offsets. As with other cycads, it isdioecious, with the males bearing cones and the females bearing groups of megasporophylls. Pollination can be done naturally by insects or artificially.
Cultivation and Uses Cycas revoluta is one of the most widely cultivated cycads, grown outdoors in warm temperate and subtropical regions, or under glass in colder areas. It grows best in sandy, well-drained soil, preferably with some organic matter. It needs good drainage or it will rot. It is fairly drought-tolerant and grows well in full sun or outdoor shade, but needs bright light when grown indoors. The leaves can bleach somewhat if moved from indoors to full sun outdoors.
Toxicity Cycad Sago Palm is extremely poisonous to animals (this includes humans) if ingested. Pets are at particular risk since they seem to find the plant very palatable Clinical symptoms of ingestion will develop within 12 hours and may include vomiting, diarrhea, weakness, seizures, liver failure, or hepatotoxicity characterized by icterus, cirrhosis, and ascites. The pet may appear bruised, have nose bleeds (epistaxis), melena (blood in the stool), hematochezia (bloody straining), and hemarthrosis (blood in the joints). The ASPCA Animal Poison Control Center estimates a fatality rate of 50 to 75 percent when ingestion of the Sago Palm is involved. The incidence of Sago Palm ingestion by pets has risen by over 200% in the last five years.If any quantity of the plant is ingested, a poison control center or doctor should be contacted immediately. Effects of ingestion can include permanent internal damage and death.
All parts of the plant are toxic; however, the seeds contain the highest level of the toxin cycasin. Cycasin causes gastrointestinal irritation, and in high enough doses, leads to liver failure. Other toxins include Beta-methylamino L-alanine, a neurotoxicamino acid, and an unidentified toxin which has been observed to cause hindlimb paralysis in Catt.
