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The below mentioned article provides a short note on lianas.
Liana (=liane) represents an ecologically specialized plant form. The plants are climbing and the specialized lianes have winding stems. It is regarded that winding is governed by light requirement. Lianes have stem that is much narrower than the length.
The winding stems are strong and pliant. The vascular system of stem is well developed and has wide vessels and sieve tubes. With the increase in length of the stem the resistance to water transport also increases. This is compensated by the development of vessels and sieve tubes with wide lumina.
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The pliancy is often accomplished by the formation of accessory cambia. These cambia form isolated vascular strands that split the stele. Pliancy is also accomplished through splitting of lignified xylem into separated thinner strands. In woody lianas, e.g. Aristolochiaceae (Fig. 29.15A) and Menispermaceae pliancy is brought about by the formation of broad medullary rays by interfascicular cambium.
Schematic illustration of anatomy of stele of lianas in cross-sectional view.
In Sapindaceae, e.g. Serjania (Fig. 29.15B), Paullinia (Fig. 29.15C), Thinouia (Fig. 29.15D) etc. the cambium ring is split into several isolated segments. The isolated cambium segments form separate vascular strands, often on a regular pattern. In between the vascular strands parenchymatous ground tissue occurs. At later stage the stem resembles a twined rope.
The stem of Bauhinia (Fig. 29.16B, C) becomes lobed owing to unequal rate of secondary growth in different sectors of cambium. The lobation of xylem increases the pliancy of the stem.
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In Bignonia (Fig. 29.16A) stem symmetrically located segments of cambium cease to form xylem inwards and donate phloem only on the peripheral side at an increased rate. As a result the xylem is split and becomes separated by radial slits. Thus the pliancy is brought about during the continued secondary growth.
Schematic illustration of the anatomy of stele of lianas in cross-sectional view.
