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Welwitschia mirabilis "Tree tumbo, tumboa." in profile.
The surface that this leaf covers helps the plant to survive at a temperature on the soil as high as 65 'C. It keeps the soil under the plant cool and moist. The leafs grow annually an average 13.8 sm. Therefore the plant can produce up to 150 m of leaf tissue over a growth period of 1000 years. The leaves are on average 1.4 mm thick. The leaves that lay on the sand surface also prevent wind erosion. Even under gale force conditions the broad leaves remain rigid and immobile. Absorbtion of water through the stomata must be regarded as very interesting, this characteristics of the leaves has ensured the species survival. The stomata remains open until the fog has lifted and although much of the water that has condensed on the leaves runs off the direct intake of a proportion of this water takes place.
Unlike other plants the stomata are open under foggy conditions and closed when it is hotter. This ensures that no water is evaporated during the heat of the day.
Most plants absorb water from the soil through their roots. This water is then transported to the stem and the leaves, the water is then lost by evaporation through the stomata. The Welwitschia mirabilis works the other way around. It absorbs water from fog through the millions of stomata on the surfaces of it's large leaves. From there the water is transported to the roots, where it is stored.
Welwitschia mirabilis is included in the following B & T World Seeds sub-lists:
Welwitschia mirabilis requires periods of "high" humidity (i.e. fogs) if it is to sustain a positive carbon balance. It may survive the absence of such conditions for 150 days - possibly much longer.
Welwitschia mirabilis is difficult to cultivate, requiring desert conditons and room to accommodate its long taproot. Rectangular pots, if possible, and at least 20cm deep. Pottery drainpipes have been used successfully. The growing medium should be 2 parts sand and gravel, 1 part loam soil and 1 part organic fertiliser (bone meal is best) it is advisable to sterilise the medium. Thouroughly moisten the mix using a dilute mild fungicide such as "Captan" (fungicide should be used for the first year).
Sow seeds on the surface and just cover with horticultural sand. The soil must be kept moist until germination, which may take from 1 week to several months (seeds are said to germinate best at about 25°C.). Place pots/seed-trays in well ventilated, warm situations, preferably with filtered sunlight as seedlings.
Temperature: 10-12°C at night, 21-23°C during the day. Light: Bright light or full sun - seeds germinate in wet years, the cotyledons photosynthesizing for 18 months. Watering: Drench thoroughly, allow to become dry between waterings.
Welwitschia mirabilis. Web page maintained by University of Connecticut Department of Ecology and Evolutionary Biology
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