Ephedra distachya: Illustration from Prof. Dr. Otto Wilhelm Thomé, Flora von Deutschland Österreich und der Schweiz, 1885, Gera, Germany (Stüber 1999).

Gnetum gnemon (Non-Flowering Plant Families (University of Hawaii Botany website)).

Welwitschia mirabilis [Dieter von Willert].

Gnetophyta

Bessey 1907

Common names

Gnetophytes.

Taxonomic notes:

The Gnetophyta have been treated as separate from other seed plants at the ranks of division (Gnetophyta Bessey 1907), subdivision (Gnetophytina Cronquist, Takht. & Zimmerm. ex Reveal 1996), class (Gnetopsida Thom 1886), subclass (Gnetidae Cronquist, Takht. & Zimmerm. ex Reveal 1996) and order (Gnetales Luerss. 1879). Among these, the ranks of subdivision or division are perhaps most appropriate in view of the extreme differences between the gnetophytes and the other seed plants. Regardless, the group is a small one, consisting of three families, each with one genus, totalling 65 species in this treatment.

For long, Gnetophytes were thought to represent a sort of primitive angiosperm. Superficially they resemble angiosperms more than gymnosperms, and some authors even suggested that they represented a derived group of angiosperms. A molecular biology study of Gnetum gnemon (Winter et al. 1999), however, found that conifers and gnetophytes are sister groups, and suggested that the evolution of flower-like reproductive structures may have occurred independently in gnetophytes and angiosperms. An independent study of chloroplast DNA from several angiosperm, gymnosperm and gnetophyte taxa (Samigullin et al. 1999) reached a similar conclusion.

Description

[I have yet to prepare a proper description of the gnetophytes.]

Range

The three Gnetophyte genera have largely disjunct distributions. Ephedra occurs mostly in semiarid and arid parts of North America, Mexico, South America (Ecuador to Patagonia and lowland Argentina), S Europe, Asia, and N Africa (including the Canary Islands) (Stevenson 1993). The other genera are exclusively tropical: Welwitschia in Africa: Angola and Namibia, and Gnetum in wet forests of Indo-Malaysia, tropical parts of West Africa, Fiji and the northern regions of South America (Schultes & Raffauf 1990).

Big Tree

Probably Gnetum gnemon.

Oldest

Probably Welwitschia mirabilis.

Dendrochronology

Not known to have been done. Most species of Gnetum are vines and thus are probably unsuitable, although the small tree Gnetum gnemon may have potential. Species of Ephedra have rings that are presumably annual and there may be potential to recover useful information, such as oxygen isotope variation, from the rings of this species. Welwitschia does not form rings.

Ethnobotany

Limited use of Gnetum and extensive pharmacological use of Ephedra; see the genus descriptions for details.

Remarks

Citations

Samigullin, T.K.; Martin, W.F.; Troitsky, A.V.; Antonov, A.S. 1999. Molecular data from the chloroplast rpoC1 gene suggest a deep and distinct dichotomy of contemporary spermatophytes into two monophyla: gymnosperms (including Gnetales) and angiosperms. Journal of Molecular Evolution 49(3):310-315. ABSTRACT: Partial sequences of the rpoC1 gene from two species of angiosperms and three species of gymnosperms (8330 base pairs) were determined and compared. The data obtained support the hypothesis that angiosperms and gymnosperms are monophyletic and none of the recent groups of the latter is sister to angiosperms.

Winter, K.U.; Becker, A.; Munster, T.; Kim, J.T.; Saedler, H.; Theissen, G. 1999. MADS-box genes reveal that gnetophytes are more closely related to conifers than to flowering plants. Proceedings of the National Academy of Sciences 96(13):7342-7347. Available: http://www.pnas.org/cgi/content/full/96/13/7342 (Accessed 2006.03.21).