Gnetophyta

Gnetophyta
Welwitschia mirabilis
Scientific classification
Kingdom: Plantae Division: Gnetophyta Class: Gnetopsida
Orders
Gnetales Welwitschiales Ephedrales

The plant division Gnetophyta or gnetophytes comprise three related families of woody plants grouped in the gymnosperms. The gnetophytes differ from other gymnosperms in having vessel elements as in the flowering plants (Angiosperms or Magnoliophytes), and on the basis of morphological data it has been suggested that Gnetophytes may be the group of spermatophytes most closely related to the flowering plants. Molecular data have suggested a closer relationship to other gymnosperms than to angiosperms (Bowe et al. 2000, Chaw et al. 2000, Soltis et al. 2002), and the conflict between morphological and molecular data has not yet been resolved. Interestingly, gnetophyte-like vessel elements have been found in the enigmatic Late Permian gigantopterids (Zi-Qiang 1999).

Gnetophyta contains only one class of living plants, class Gnetopsida. The class includes three extant genera, which in some classifications are placed in a single order (Gnetales) but in others distributed among three orders, each containing a single family and genus:

• Gnetales: Gnetaceae; Gnetum
• Welwitschiales: Welwitschiaceae; Welwitschia
• Ephedrales: Ephedraceae; Ephedra

The Gnetales consist of a single genus, Gnetum, which are mostly woody climbers in tropical forests. However, the most well-known member of this group, Gnetum gnemon, is a tree. Its seeds are used to produce a crispy krupuk snack known as emping or krupuk belinjo.

The Welwitschiales comprise only one species, Welwitschia mirabilis. It grows only in the deserts of Namibia and Angola. The plant is strange in having only two large strap-like leaves for all its life. These grow continuously from the base, and are usually tattered at the ends by flapping in the winds.

The Ephedrales consist of a single genus Ephedra, and are known as the jointfirs because they have long slender branches which bear tiny scale-like leaves at their nodes. Ephedra has been traditionally used as a stimulant, but is a controlled substance today in many juristictions because of the risk of harmful or even fatal overdosing.

References

• Bowe, L. Michelle; Coat, Gwénaële & dePamphilis, Claude W. (2000): Phylogeny of seed plants based on all three genomic compartments: Extant gymnosperms are monophyletic and Gnetales' closest relatives are conifers. PNAS 97: 4092-4097.
• Chaw, Shu-Miaw; Parkinson, Christopher L.; Cheng, Yuchang; Vincent, Thomas M. & Palmer, Jeffrey D. (2000): Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers. PNAS 97: 4086-4091. PDF fulltext
• Soltis, Douglas E.; Soltis, Pamela S. & Zanis, Michael J. (2002): Phylogeny of seed plants based on evidence from eight genes. American Journal of Botany 89: 1670-1681 PDF fulltext
• Zi-Qiang, Wang (1999): Gigantonoclea: an enigmatic Permian plant from North China. Palaeontology 42(2): 329–373. doi:10.1111/1475-4983.00076 (HTML abstract)

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