Tree ferns

(botany) The common name for plants belonging to the families Cyatheaceae and Dicksoniaceae; all are ferns that exhibit an arborescent habit.

Plants belonging to the families Cyatheaceae and Dicksoniaceae, whose members typically develop tall trunks crowned with leaves (fronds) which often reach some 20 ft (6.1 m) in length and 5–6 ft (1.5–1.8 m) in width. Tree ferns reach their greatest development in the rainforests and cloud forests of the mountainous tropics. See also Rainforest.

Tree fern trunks may reach 65 ft (19.8 m) tall; their diameters vary from 0.4 in. (1.0 cm) to 4 ft (1.2 m). The lower trunk is often densely covered with matted adventitious roots which greatly increase its diameter. Certain specimens branch near the base of the trunk or higher up; perhaps this branching occurs in response to injury.

The degree of division of the leaves varies from simple to four or five pinnate. The leaflets (pinnae) are usually smaller toward the base of the leaf; when these basal leaflets are branched into threadlike divisions, they are called aphlebiae. The Dicksoniaceae have marginal sori terminal on the veins and protected by a bivalved indusium. The Cyatheaceae produce sori well away from the margin, usually seated at the forking of a vein or midway along a simple vein.

The typical vascular system of both families is dictyostelic. The Cyatheaceae have accessory vascular strands in the pith and cortex. Fibrous sheaths around the vascular tissue and just inside the epidermis provide mechanical support. The xylem consists of scalariform tracheids and parenchyma, the phloem of sieve tubes and parenchyma. Numerous mucilage canals are embedded in the pith and cortex. See also Stem; Tree.