Welwitschia is a monotypic genus of gnetophytes containing only the species Welwitschia mirabilis. It is named after the Austrian botanist Friedrich Welwitsch, who documented the plant in the 1850s. In common use, it is sometimes referred to as the tree tumbo. It is native to Angola and Namibia, where it grows in the extreme conditions of the Namib desert, tolerating high heat and low precipitation. Welwitschia is the only living genus of the family Welwitschiaceae and order Welwitschiales, and is one of three extant genera of gnetophytes, alongside Gnetum and Ephedra.

Welwitschia is well known for its unique morphology. The plant has only two leaves that grow out of a large woody stem, known as a crown, and continue to grow throughout the plant's life. Welwitschia is one of the longest-living plants on Earth, with some individuals being thousands of years old. Because of the long lifespan the leaves can become quite large, often reaching several meters in length.

As a gymnosperm, Welwitschia uses cones to reproduce. Both male and female plants produce nectar from their cones that attract insects that then carry the pollen to other plants. The species is not currently in any significant danger of extinction, in part because its long lifespan insulates it from temporary reproductive struggles. Despite this, Welwitschia is susceptible to future overgrazing and disease, because it grows in only one environment.

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