Welwitschia's World, by Joh Henschel

Welwitschia's World, by Joh Henschel. ISBN 9789991687865 / ISBN 978-99916-878-6-5

Welwitschia's World, by Joh Henschel. ISBN 9789991687865 / ISBN 978-99916-878-6-5

We have entered Welwitschia’s World, and in doing so, stand in awe. Joh Henschel celebrates the ancient Welwitschia with this book.

Joh Henschel  

Welwitschia mirabilis in a nutshell

The tree, Welwitschia mirabilis, is the only member of the family welwitschiaceae, order Welwitschiales, division Gnetophyta. Although the welwitschia is a gymnosperm (related to conifers), it has a number of similarities to angiosperms, such as having flowers, pollen transfer by insects, not wind, as well as the characteristics of the water-conducting system (xylem vessel elements). Welwitschias occur in the northern half of the Namib Desert, between the Kuiseb River in Namibia, south-east of the harbour town Walvis Bay, and the Giraul River in Angola, north-east of the harbour town Namibe. Within this range, they occur in some thirty patches. It is thought that 100 million years ago the population of welwitschias was more connected across this range than today. Welwitschia mirabilis was officially described and classified in 1861 by the famous London botanist, Joseph D. Hooker, and named after the Austrian naturalist Friedrich Martin Joseph Welwitsch, who had sent the first specimen from Angola to Hooker in 1859. Soon after, the explorer and artist Thomas Baines found this plant in Namibia. The desert people, Himba and Topnaar, respectively call welwitschias onyanga and Ikharos. They also refer to it as tumboa, meaning 'stump', because of the short, abrupt stem of this tree. The abruptly ending unbranched stem is actually the result of a closed system of growth following the early death of the shoot apex. Welwitschias have two separate sexes. Females produce cones. Males have narrower spindles, which bear tiny yellow flowers. Females normally produce numerous winged seeds every year, which are dispersed by wind. However, the seeds are very prone to being infected with a fungus, Aspergillus niger, which quickly renders them unviable. Welwitschia plants can grow very old, although the actual age has been established only for a few individuals by carbon-14 dating. The oldest determined age was 920 years, and a few others were found to be 300-550 years old. It is thought that big plants may get older, perhaps 1500-2000 years, but that is conjecture. Age estimation by size alone is uncertain because it was found that growth rates vary considerably between individuals. The leaves are the longest-lived leaves in the plant kingdom, as they persist for the plant's lifespan. The welwitschia has only two broad, thick, leathery leaves, which are often split and frayed, giving the appearance of many. The living portion of leaves can reach nearly four metres long and almost two metres wide, but are often damaged and shortened. The leaf area is unusually large for a desert plant. Leaf area of an average healthy adult plant is about one square metre (the maximum measured was 21). Leaves are evergreen, growing continuously throughout the year at about 14 centimetres per year (range 7-30). Leaf growth rate differs considerably between seasons, years, and different locations in the landscape where plants grow. The plant usually opens its stomata (pores) by day to take up carbon dioxide while photosynthesising. Its transpiration rates of water are therefore surprisingly high for a desert plant: a medium-sized plant requires about one litre per day (ranging from 53 millilitres to 2.6 litres). In times of water stress, welwitschias can switch to another method of respiration and carbon uptake (CAM) by night when the air is coo! and moist. In this case the plant keeps its stomata closed by day so as to reduce water loss. It can also obtain some carbon for photosynthesis from reserves in older leaf parts. The plant then goes into net carbon deficit and replenishes this reserve when conditions improve. Welwitschias obtain water from several sources. Rain water that infiltrates into the hard, stony soil and lingers at shallow levels appears to be very important for welwitschias. This is somewhat surprising, given the scarcity of rainfall in the Namib. [...]

This is an excerpt from the book: Welwitschia's World, by Joh Henschel.

Title: Welwitschia's World
Author: Joh Henschel
Publisher: Wordweaver Publishing House
Windhoek, Namibia 2012
ISBN 9789991687865 / ISBN 978-99916-878-6-5
Softcover, 15x21 cm, 66 pages, 100 full-colour photographs

Henschel, Joh im Namibiana-Buchangebot

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