cycad

cycad , any plant of the order Cycadales, tropical and subtropical palmlike evergreens. The cycads, ginkgoes , and conifers comprise the three major orders of gymnosperms, or cone-bearing plants (see cone and plant ). The cycads first appeared in the Permian period. They are the most primitive of the living seed-bearing plants and in many ways resemble the ferns . Some have tuberous underground stems, with the crown of leathery, glossy, fernlike leaves springing from ground level; others have a columnar stem, usually 6 to 10 ft (1.8-3.1 m) high (though the corcho of Cuba reaches 30 ft/9.1 m), and are often mistaken for palms. There are 11 genera composed of less than 150 species, some found in very restricted areas. Many cycads (e.g., the fern palm of the Old World tropics and the nut palm of Australia) bear poisonous nutlike seeds. The pith of the coontie ( Zamia floridana ) yields a starch called Florida arrowroot or sago ; the coontie is often called sago palm. Cycads are grown as ornamentals in warm regions and in greenhouses. The cycads are classified in the division Pinophyta , class Cycadopsida.

cycad Phylum (Cycadophyta) of primitive palm-like shrubs and trees that grow in tropical and subtropical regions. Although they are gymnosperms, they have feathery palm- or fern-like leaves (poisonous in most species) at the top of stout (usually unbranched) stems. In addition to their main roots, they also have special roots containing cyanobacteria that carry out nitrogen fixation. These plants first flourished c.225 million years ago. Most of the 100 or so surviving species are less than 6m (20ft) tall.