**1. Cycad Description and Taxonomy:**
– Cycads have a rosette of pinnate leaves around a cylindrical trunk.
– Trunks are usually unbranched but some types can branch.
– Apex of the stem is protected by modified leaves called cataphylls.
– Leaves grow directly from the trunk and fall when older, leaving a crown at the top.
– Leaves are pinnate, with parallel ribs emerging from a central leaf stalk.
– Cycads are gymnosperms with cones, not closely related to palms which are angiosperms with flowers.
– Living cycads belong to Cycadales, with families Cycadaceae and Zamiaceae.
– Cycads are more related to Ginkgo than other gymnosperms.
– Cycads reached diversity peak during the Mesozoic era.
**2. Cycad Distribution and Decline:**
– Living cycads are found in subtropical and tropical regions worldwide.
– Greatest diversity is in South and Central America, also present in Mexico, Australia, Japan, China, and parts of Africa.
– Some species can survive in harsh desert conditions, others in rainforests.
– Cycads can grow in various soil types, light conditions, and climates.
– Cycads globally are declining, with some species close to extinction.
– Four species are on the brink of extinction, and seven species have fewer than 100 plants left in the wild.
– Threats include habitat loss, illegal harvesting, and climate change.
– Conservation efforts are crucial to protect remaining populations.
**3. Cultural Significance of Cycads:**
– Cycad known as namele in Vanuatu, an important symbol of traditional culture.
– Taboo sign in Vanuatu, appears on national flag and coat of arms, gives name to Nagriamel indigenous political movement.
**4. Cycad Cultivation, Habitat, Nitrogen Fixation, and Toxicity:**
– Cycads have a unique habitat and cultivation requirements.
– They are often grown for their ornamental value.
– Some cycad species are endangered due to habitat loss.
– Cycads have a symbiotic relationship with nitrogen-fixing bacteria, essential for growth and development.
– They play a role in enriching the soil with nitrogen and thrive in nutrient-poor soils.
– Some cycad species contain toxins harmful to animals, acting as a defense mechanism against herbivores.
**5. Cycad Conservation, Legal Issues, and Notable Publications:**
– Conservation efforts are underway to protect endangered cycad species.
– Illegal trade and smuggling pose a threat to their survival.
– International regulations restrict the trade of certain cycad species.
– Cycad conservation involves habitat preservation and restoration, with public awareness and education playing a crucial role.
– Notable publications related to cycads include studies on their genome, evolution, and conservation strategies.
Cycads /ˈsaɪkædz/ 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 very slowly and live very long. Because of their superficial resemblance, they are sometimes mistaken for palms or ferns, but they are not closely related to either group.
| Cycadales Temporal range:
| |
|---|---|
| |
| Cycas rumphii with old and new male strobili. | |
Scientific classification 
| |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Spermatophytes |
| Clade: | Gymnospermae |
| Division: | Cycadophyta Bessey 1907: 321. |
| Class: | Cycadopsida Brongn. |
| Order: | Cycadales Pers. ex Bercht. & J. Presl |
| Extant groupings | |
| Synonyms | |
| |
.jpg)
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.
Cycads 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. Another defence mechanism against herbivores is the accumulation of toxins in seeds and vegetative tissues; through horizontal gene transfer, cycads have acquired a family of genes (fitD) from a microbial organism, most likely a fungus, 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.