An order of the class Cycadopsida having one species, Welwitschia mirabilis. This plant is native to the very arid deserts of southwestern Africa. Its appearance is bizarre—it has a very short, unbranched, woody stem (sometimes to 3 ft or 1 m in diameter), which is cushion- or saucer-shaped and tapers quickly to a long taproot. There are only two leaves, and these persist throughout the life of the plant. The leaf is broadly strap-shaped, as wide as the stem, firm, and leathery, and gradually splits lengthwise between the veins. The leaf (of indefinite growth) develops from a meristem at its point of connection to the stem. The species is dioecious; the cones are borne on branched axes originating between the crown of the stem and the base of the leaf. The order is known only from the one living species and not from any fossils.
- 词性: noun
- 行业/领域: 科学
- 类别 普通科学
- Company: McGraw-Hill
创建者
- Francisb
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