How do the leaves of Welwitschia mirabilis keep growing throughout the plant’s life?

The two permanent, straplike leaves of Welwitschia mirabilis grow throughout the plant’s life due to a specialized region of tissue called the basal meristem.12

Shortly after the plant germinates and produces its initial cotyledons, growth activity shifts away from the stem's tip to the base of these two permanent leaves. This meristematic zone continuously adds new tissue to the base of each leaf at a rate of approximately 8 to 15 cm (3 to 6 inches) per year.21

While the leaves grow outward from this base, their total length is typically kept to about 3 metres (nearly 10 feet) because the tips are constantly eroded by hot desert sand. Over time, this process causes the leaves to become split and frayed, often giving the appearance of multiple leaves rather than the original pair.12