Hooked Spine Arrangement of Uncaria rhynchophylla (Rubiaceae)

Abstract

Uncaria rhynchophylla (Rubiaceae) is a liana that climbs by means of hooked spines. The spines have been used as an important crude drug in China and Japan. In stems growing horizontally, nodes with a single spine and nodes with two spines appear alternately, but in stems growing upright, nodes with two spines are continuous. The unique arrangement of spines has been interpreted variously. A new idea on the alternating single and double spines is proposed. The leaves of U. rhynchophylla are decussate. If the two opposing leaves of a pair from a single node lean on the objective (the host), one of the leaves in the succeeding pair of leaves may not come in contact with the host. This appears to be the reason for the alternating nodes with single and paired spines. In the former case, production of spines is restrained during the early stages of growth and development.