Today I’m introducing one of the most bizarre plant species in the world. Found in the Namib desert, in Namibia and Angola, the Welwitschia mirabilis, usually simply called welwitschia or tree tumbo in English, is the solely member of the order Welwitschiales, a group of gymnosperms in the division Gnetophyta.
A specimen of Welwitschia mirabilis in Naukluft, Namibia.
The tree tumbo has a unique appearance. The seedlings have two cotyledons (the original leaves produced by the seed) and later develop two permanent leaves that grow opposite (at right angles) to the cotyledons. These permanent leaves grow continuosly, reaching up to 4 m in length. While growing, the leaves split and fray into several straps and occupy an area of about 8 m in circunference around the plant. The stem is woody and the flowers appear on a central part called crown. The species is dioecious, meaning that male and female flowers appear in different plants. Pollination is usually carried out by insects.
Living up to 2 thousand years, the tree tumbo is a very peculiar desert plant. Its leaves are broad and very large, different from what is the rule in the desert. Its root system is also very shallow, not penetrating deep in the ground. It seems that most of the water used by the plant is captured by the leaves from the morning fog.
Although having a very restrict range, the tree tumbo is not (yet) and endangered plant, as its population is considerably large. However, due to its popularity, some areas attract collectors, and since its growth is so slow, it may eventually become a vulnerable plant.
Unlike typical desert plants, such as succulents—which store as much water as possible in thick stems or leaves—the tree tumbo has very thin leaves that absorb moisture from fog effectively but store almost none. Instead, water is stored in the trunk, most of which is underground. Beneath the trunk, a long taproot extends an additional several meters deep; this serves both to anchor the plant in high winds and to absorb moisture from deep underground.
One of a KindAlmost everything about the plant makes it extremely hard to categorize. It has many of the characteristics of tropical plants, even though it lives only in the desert. Its seeds form on cones somewhat like those of a pine tree. That makes the Welwitschia a gymnosperm, but because it’s so unlike other gymnosperms in most respects, it doesn’t neatly fit anywhere in the plant kingdom. So this species is the lone member of a genus, which is in turn the lone member of a family in the Gnetales order of gymnosperms—itself a small and diverse order. Austrian botanist Friedrich Welwitsch is credited with the plant’s discovery and description in 1859, and it therefore bears his name.
Despite the fact that the tree tumbo appears in just one small part of the world, it’s not considered endangered—there are plenty of them. (They can also, with some effort and patience, be cultivated in greenhouses and other environments.) All the same, I think it would be safer for the plants if I stayed far away from the Namib desert.