Virtually all plants and all plant parts rotate slightly about a central axis, a movement called circumnutation. While all plants circumnutate, vines show exaggerated circumnutation. This study contrasts circumnutation in two congeneric twining vines, and examines the consequences of differences in circumnutation behavior on the ability of the vines to search for climbing supports. Lonicera japonica and L. sempervirens were grown in a common garden. Local climbing supports were placed adjacent to plants and distant supports were placed 1.5m away. Both species produced vertically oriented shoots that circumnuted at similar rates (about 40 compass degrees per hour). Vertically oriented shoots of both species successfully found and climbed local supports at the same rate. However, the species differed in the behavior of horizontally oriented shoots. Horizontal shoots produced by L. japonica had reduced circumnutation compared to vertical L. japonica shoots. In contrast, horizontal shoots of L. sempervirens continued to circumnutate at rates equal to vertical shoots. The horizontal shoots of both species root at the nodes (100% rooting success for nodes less than 2 cm above the ground surface), and thus function as stolons. The reduced circumnutation rate of L. japonica horizontal shoots resulted in straight growing shoots with 21% of the nodes less than 2cm above the ground. In contrast, the continued circumnutation of L. sempervirens horizontal shoots resulted in shoots that spiraled across the ground with only 8% of the nodes less than 2cm above the ground. The capacity of L. japonica to produce shoots with specialized circumnutation behavior allowed it to climb local supports and establish more rooted nodes near distant supports, while the lack of shoot specialization in L. sempervirens resulted in it being less effective in placing rooted nodes near distant supports.

Key words: circumnutation, foraging, Lonicera japonica, Lonicera sempervirens, vines