The families of gymnosperms

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L. Watson and M. J. Dallwitz

Welwitschiaceae

Vegetative. Very strangely pachycaul; evergreen; a long-lived, woody herbaceous perennial, the woody, tap-rooted stem widening into a concave disc up to a metre across. A bizarre southern African gymnospermous monotypic with a short, woody, unbranched stem bearing only 2 (rarely 3) strap-shaped amphistomatous leaves, the latter continuing to grow from basal meristems throughout the long life of the plant, spreading laterally along the ground, progressively fraying and twisting. Mature leaves strap-shaped and very peculiar, but simple; broad and flat (the veins sub-parallel, some of them anastomosing or terminating blindly).

Reproductive organization. Dioecious (and entomophilous). The reproductive structures organized like reduced angiosperm flowers (with stamen-like antherophores, but with exposed, gymnospermous ovules). The female flowers borne in dichasially branching inflorescences arising from a series of transverse ridges parallel with and internal to the leaf bases. Each inflorescence branch terminates in a regular cone with opposite or decussate scales which are red at maturity. The flowers with a tubular perianth seemingly homolgous with the two members of the outer whorl of the male flower (q.v.), one erect ovule, and no rudimentary stamens. The ovules borne in female cones (with solitary female flowers the axils of the scales). The seed-cone scales opposite and decussate. The ovules borne erect in the centre of the “flowers”; orthotropus (with an elongated, tubular micropyle); 1 integumented, or 2 integumented (if the outer one is interpreted as perianth).

Male flowers borne like those of female plants in dichasially branching inflorescences arising from a series of transverse ridges parallel with and internal to the leaf bases. The male flowers in bract axils, with the outer whorl of their 2+2 perianth transverse to the bract, 6 stamens united below, with 3-locular anthers, and a rudimentary gynoecium. Pollination involving a “liquid drop” mechanism; anemophilous, but with partial entomophily.

Seeds and seedlings. Seeds usually maturing only one per cone, winged (via a broad wing developed from the outer “integument”). Cotyledons 2 (persisting after germination for 1–2 years).

Wood anatomy. Secondary xylem with vessels.

Geography, cytology. Temperate to sub-tropical; confined to SW Africa, with a disjunct distribution there.

Taxonomy. 1 species; Welwitschia. Order Gnetales.

Miscellaneous. • Welwitschia: habit and technical details (Le Maout and Decaisne). • Welwitschia: details (Sporne).


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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2008 onwards. The families of gymnosperms. Version: 9th April 2015. delta-intkey.com’.

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