The Vascularization of Ferns

Plant Vascular System

• A plant's vascular system includes the roots, stems and veins. Water is conducted through the vascular system by two vascular tissues called xylem and phloem. Xylem is actually a series of dead tube-shaped cells that function like tiny water pipes within the vascular system. Phloem is also a series of tubes, but these tubes contain living tissue through which nutrients and sugar move throughout the plant.

Fern Vascular System

• Ferns have roots that hold them into the ground, but also pull water and nutrients from the soil for delivery to the rest of the plant. Growing up from the base of the plant are several stems that lead to the fern's leaves, more accurately called "fronds." Looking closely at a fern frond, you will see veins branching off the central stem (the rachis) to the leaflets. This visible vein runs down the center of each leaflet and is part of the fern's vascular system.

Fern Venation

• Ferns have a branching pattern of leaf venation. A split occurs at the end of each vein until a network of tiny veins extends throughout the frond. This is referred to as dichotomus venation. Ferns such as sword ferns and bracken ferns have pinnately arranged venation, where veins split off at various points from a central vein. Maidenhair and similar ferns have veins with a palmate arrangement where side veins split off from a single point of the central vein.

Benefits of Vascularization

• Plants such as mosses and liverworts don't have true vascular systems. Instead, they must absorb water directly from the ground. This limits the size of these plants because all their tissues must stay in contact with moist soil to stay alive. With vascular tissue, ferns could grow fronds well above the soil and could withstand occasional dry conditions.