Black tree fern stem. Cross-section of a black tree fern stem (Cyathea medularis). This fern grows to 30 metres in height, supported by its wood-like stem. The stem carries the plant's vascular system, providing nutrients and water to the fronds (leaves) along its length and removing waste. The fronds attach to the stem via leaf bases or stipes, which have a characteristic shape when the trunk is sectioned, resembling the Greek letter omega (W-shaped). They are seen here arranged around the circumference of the stem. The trunks of this fern are used to build huts and small houses in the tropics. C. medularis is native to New Zealand, Fiji and Polynesia.