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Leaves lose water primarily through their stomata, the pores needed for gas exchange, and most desert plants minimize the number of these microscopic openings and locate them on the lower leaf surface. Welwitschia’s leaves have about 250 stomata per 0.0016 square inch, more than most temperate and tropical plants, and these are located on both the upper and the lower leaf surfaces. In short, this plant is both a botanical and a physiological paradox of desert adaptation that could not have been fully appreciated by Welwitsch when he first found and described it, even though he wrote, “I am convinced that what I have seen is the most beautiful and majestic that tropical South Africa has to offer.”

Leaf stomates typically stay open during the day to allow carbon dioxide to diffuse in so that it can become fixed into small carbon compounds during the process of photosynthesis, in which sugar is produced. Water then necessarily evaporates, leaving passively through the open stomates, especially when the leaves are heated by the sun and the air is dry. However, most desert plants (in this case including Welwitschia), have evolved the ability to conserve water by closing their stomata during the day when water loss would be high, and they have a special mechanism that still allows them to perform photosynthesis. They conserve water by opening their stomates at night when the air is cooler and more saturated with water. And the carbon dioxide then enters (it can’t be used for photosynthesis just then, because there is no sunshine) following the diffusion gradient (from high concentration outside to low concentration inside the leaf ). The gas concentration is lowered inside the leaf as gas that enters is removed (by being incorporated and thereby stored) in malic acid. Then, in the daytime, the reaction reverses itself—the malic acid breaks down and releases the carbon dioxide, which stays inside because the stomates are closed then. The stomates are closed to conserve water, and the carbon dioxide then held captive is available to be used in the normal way to make sugar by photosynthesis. Despite this water conservation—a trick that is also used by many other desert plants—Welwitschia still needs water, and it employs a mechanism like that of the “butt-head” tenebrionid beetles who inhabit the same environment: the capture of water condensed from the air. It has no mouth, though, to suck this water up.

Welwitschia’s stomates are arranged in troughs formed by parallel ridges on its leaves. These ridges are much like the ridges on the tenebrionid beetles’ backs, and function as they do in catching water vapor. Water that condenses on cold nights runs between the ridges, along the troughs, where it is absorbed by these stomates.

According to NASA’s definition, life is “a self-sustaining chemical system capable of undergoing Darwinian evolution.” Almost all signs of the chemistry of life point to one origin here on Earth. Despite the great diversity of forms, the internal machinery of life on our planet may be so conservative because all life here evolved from common ancestry: all organisms are constrained by their evolutionary history. However, life as we know it is also constrained by the physical properties of the elements that compose it, and that possibly further constrain it into its specific configurations by temperature and pressure. We assume that life is not likely ever to be radically different from ours, or in all the billions of solar systems where it is almost certain to exist, to have existed, or to exist in the future. When (in 2007) astronomers discovered Gliese 581c, another of 227 new planets discovered thus far, it generated excitement because its distance from its sun and its size suggested that its temperatures probably ranged from 32° to 104°F, conditions that are just right for the possibility of liquid water. Hence it is one of the first planets thought hospitable to life. We automatically make the assumption that life requires certain conditions regardless of where it is found