How do tree ferns grow tall without producing woody secondary growth?

Tree ferns grow tall without producing woody secondary growth because their trunks are formed entirely by primary growth originating from the stem apex. Unlike many other trees that increase in diameter through a vascular cambium, tree ferns lack this meristematic layer and therefore do not develop secondary xylem (wood) or secondary phloem.12

Instead, their structural integrity is achieved through other means:

• Strengthening tissues: The stems are reinforced by specialized supporting tissues that surround the vascular bundles.1
• Root mantle: In some species, the trunk is further stabilized by a dense, protective mantle of adventitious roots that grow down along the stem, providing additional support and anchorage.1

Because they rely on these primary tissues rather than secondary thickening, the diameter of a tree fern's trunk is determined at the apex during its initial development and does not increase significantly as the plant grows taller.12