The Families of Gymnosperms |  |
Gnetaceae
Vegetative. Evergreen; small trees (a few), or shrubs, or vines (mostly). The leafy branchlets not flattened. Mature leaves simple; broad and flat (elliptic, angiosperm-like, with reticulate venation, exstipulate, leathery, with hydathodes); not clustered; opposite and decussate.
Reproductive organization. Monoecious, or dioecious (mostly). The reproductive structures organized like reduced angiosperm flowers (with stamen-like antherophores, but with exposed, gymnospermous ovules). The female flowers borne in spikes, which are often grouped into more complex inflorescences. The spikes bear decussate bracts, in the axils of which are condensed partial inflorescences of about 3–8 female flowers, which form whorls round the stem and are intermingled with numerous hairlike structures. The female flower has a tubular perianth, cf. that ofEphedra, around the single, apparently 2-integumented ovule. After fertilization, the perianth becomes fleshy, the outer integument becomes woody, and the whole forms a drupe-like fruit. The ovules not in cones (being produced in the female “flowers” of uncertain morphological interpretation, in whorls on the spikelike inflorescence axes, each whorl subtended by a fleshy collar); borne erect in the centre of the “flowers”; orthotropus (with a long, projecting, tubular micropyle); 2 integumented (if the outer layer is interpreted as a perianth), or 3 integumented.
The male flowers in spikes, these often grouped into more complex inflorescences. The spike bears decussate bracts, in the axils of which are condensed, partial inflorescences of up to 40 flowers. The effectively whorled flowers are intermingled with hairlike structures. At the top of each nodal group in the male inflorescence there is usually a single ring of female flowers, which are rarely fertile. Male flowers with a tubular (2-membered) perianth, and at the top of the projecting axis, right and left, are two sessile unilocular anthers. Pollen without air bladders. Pollination mostly anemophilous, but entomophily associated with nectar secretion is known in a few species; involving a “liquid drop” mechanism.
Seeds and seedlings. Seeds wingless. Cotyledons 2.
Wood anatomy. Secondary xylem with vessels.
Geography, cytology. Sub-tropical and tropical; Indomalaysia, tropical parts of West Africa, Fiji and the northern regions of South America.
Taxonomy. About 30 species; Gnetum. Order Gnetales.
Comments. Flowers monosexual, in catkin-like formations; the male flower consists of a stamen and perianth, and female flower of an ovule with 2 integuments and perianth.
Miscellaneous. • Gnetum: habit and technical details (Sporne). • Gnetum gnemon: technical details (Lindley).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2008 onwards. The families of gymnosperms. Version: 6th November 2009. http://delta-intkey.com’.
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