Population variation of leaflet sleep movements in Oxalis grandis (Oxalidaceae)

To identify intraspecific variation in the expression of circadian leaflet movements, we observed changes in leaflet elevation angle in a controlled environment and in the field. Two morphologically and ecologically distinct populations of Oxalis grandis were compared: a typical mesic forest ecotype and an atypical, densely hirsute ecotype found on partially exposed shale outcroppings. Significant genotypic variation was detected within both populations. The controlled environment experiment revealed significant differences in the intrinsic rhythm between the two populations, primarily at the beginning and end of the photophase. We observed leaflet ascent and descent prior to lights‐on and lights‐off, respectively, processes we define as anticipatory. Hirsute ecotype plants showed a greater anticipation of lights‐on, whereas the mesic ecotype plants showed a greater anticipation of lights‐off. In the field, significant differences in leaflet elevation between the populations occurred in early morning and late afternoon, but not immediately preceding dusk. Contrary to the controlled environment experiment, mesic ecotype plants showed greater anticipation of dawn; plants from both populations showed similar anticipation of dusk. Plants of the hirsute ecotype exhibited higher sensitivity to sudden fluctuations in light level. We hypothesize that differences in light sensitivity partially explain the differences in the leaflet angle patterns between the field and controlled environments.