EFFECT OF NONRANDOM LEAF ORIENTATION ON REPRODUCTION IN LACTUCA SERRIOLA L.

The cauline leaves of an annual, Lactuca serriola L., are naturally oriented vertically with the lamina perpendicular to the east and west. Previous physiological data indicated that this nonrandom leaf orientation should reduce water loss without substantially reducing photosynthesis and could thus influence plant growth and reproduction (Werk and Ehleringer, 1984, 1985). The effect of leaf orientation on flower and seed production was tested experimentally using potted L. serriola grown outdoors. Leaves of half the plants were forced to remain approximately horizontal while the other plants were allowed to orient naturally. The plants with horizontal leaves lost water more rapidly than the plants with naturally oriented leaves. Above-ground weight, below-ground weight, seed weight, and the number of seeds per flower were not significantly affected by leaf orientation. Flower production was a linear function of plant size for both treatments with plants with natural leaf orientation having a significantly greater slope. These results indicate that the nonrandom leaf orientation observed in L. serriola is a morphological character which can enhance reproduction. © 1986 The Society for the Study of Evolution.