Scientific name: CycadopsidaEnglish name: CycadsVietnamese name: Tuế, Thiên tuếOther name:
Cycads retain some fern-like features, notably pinnate leaves and circinate vernation. However, they (usually) produce cones of nonphotosynthetic reproductive structures. These cones are unisexual, in fact the plants are dioecious, having separate male and female plants. Cycads were much more prominent in the forsts of the Mesozoic than they are today. Presently, they are restricted to the tropics. Zamia floridana is the only cycad occurring natively in the continental United States. Several species of Cycas, notably C. revoluta, are commonly encountered cultivated plants in warm, moist areas. Cycas revoluta leaves are often used in Palm Sunday services.
Cycads are an ancient group of seed plants characterized by a large crown of compound leaves and a stout trunk. They are evergreen, gymnospermous, dioecious plants having large pinnately compound leaves. They are frequently confused with and mistaken for palms or ferns, but are related to neither, belonging to the class Cycadopsida.
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), Australia, the Pacific Islands, Japan, China, India, Madagascar, and southern and tropical Africa, where at least 65 species occur. Some are renowned for survival in harsh semi-desert climates, and can grow in sand or even on rock. They are able to grow in full sun or shade, and some are salt tolerant. Though they are a minor component of the plant kingdom today, during the Jurassic period they were extremely common. Sago flour is generally made from true palms - not from the cycad popularly known as "Sago Palm" (Cycas revoluta).
They have very specialized pollinators and have been reported to fix nitrogen in association with a cyanobacterium living in the roots. This blue-green algae produces a neurotoxin called BMAA that is found in the seeds of cycads.