Zanoni, Thomas A. Jardín Botánico Nacional, Santo Domingo, Dominican Republic; New York Botanical Garden, New York, New York.
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An order of gymnosperms represented by one species, Welwitschia mirabilis. The plant W. mirabilis (see illustration) is native to the very arid deserts of Namibia and Angola in southwestern Africa. Its appearance is bizarre; It has a very short, unbranched, woody stem [sometimes 1 m (3.3 ft) in diameter], which is cushion- or saucer-shaped and tapers quickly to a long taproot. There are only two leaves, which persist throughout the life of the plant. The leaves are broadly strap-shaped, as wide as the stem, firm, and leathery, and they gradually split lengthwise between the veins. Each leaf [of indefinite growth, but known to reach 7 m (23 ft) in length] develops from a meristem at its point of connection to the stem. The species is dioecious; the cones are borne on branched axes that originate between the crown of the stem and the base of the leaf. Welwitschia mirabilis is the only known living species, and no fossils have been found. However, the taxonomic position of Welwitschia has been a source of contention, with the species being placed in various classes (for example, Cycadopsida or Gnetopsida) and with Welwitschiales being subsumed into the order Gnetales, depending on the classification. See also: Cycadopsida; Gnetales; Pinophyta; Plant kingdom
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