Welwitschia mirabilis: morphology of the seedling
Seedlings of Welwitschia mirabilis Hooker were grown from seeds collected on the Welwitschia Fläche at the confluence of the Khan and Swakop Rivers in South-West Africa. Germination is epigeous. Two lanceolate cotyledons constitute the first photosynthetic organs. They reach maximum size in about 9 1/2 weeks, but apparently remain photosynthetically functional for approximately 1 1/2 years. The only pair of foliage leaves are opposite and decussately arranged with respect to the cotyledons. The strap-shaped foliage leaves grow indefinitely from a basal meristem and increase in width by intercalary growth. Another pair of foliar structures is produced by the shoot apex before it becomes meristematically inactive, but they do not develop into foliage leaves. At first narrow and triangular in shape, these primordial leaves gradually thicken and extend laterally, burying the shoot tip. The bases of the foliage leaves become ensheathed in deep grooves which are formed during the development of meristematically active ridges on both sides of the leaves Strobili of adult plants are usually borne on the inner ridge. The seedling root system is not extensive and appears to serve mainly for anchorage. As Welwitschia tends to be confined to a narrow fog belt, it seems feasible that fog condensate, absorbed through the stomata, constitutes its main water supply. Keywords: welwitschia mirabilis, seedling, gnetum, Namib.
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