Morphological plasticity of the clonal herb <i>Lamiastrum galeobdolon</i> (L.) Ehrend. &amp; Polatschek in response to partial shading

SUMMARY The present experiment investigates the morphological plasticity of Lamiastrum galeobdolon (L.) Ehrend. & Polatschek in response to light patchiness. In a garden experiment, stolons of the plant were grown under the following six light regimes: high light, low light, from low light to high light, from high light to low light, under high light but with the apical region of the stolon under low light, and under low light but with the apical region under high light. The low-light conditions provided 50% of high light PAR and 28% of high light R/FR ratio (ratio of red to far red light), and simulated the canopy-like shade that may be relevant to this species in its natural habitat. Plants growing under different light treatments did not show significant differences in total plant dry weight, total number of ramets, number of primary ramets, number of secondary ramets, and number of branches per clone. L. galeobdolon plants growing under high-light conditions formed shorter internodes, shorter petioles and smaller laminas with lower SLA, and showed higher branching intensity than those growing under low-light conditions. Accordingly, when growing between patches of different light conditions, the primary ramets had shorter internodes, shorter petioles and smaller laminas with lower SLA in high-light than in low-light patches. Exposing the apical region, of an otherwise shaded stolon, to high light shortened its internodes, compared with those of plants growing entirely under low-light conditions. Shading the apical region, of otherwise unshaded stolon, had no effect on the lengths of these internodes. In contrast, the morphology of the leaf responded to local light conditions only. Elongation of stolon internodes was completed much faster (within 2 or 3 wk) than lamina expansion and petiole extension, which took at least 6 wk. These results are interpreted in terms of the efficiency of exploitation of high-light patches within the habitat of L. galeobdolon.