Formation of false stems in Cymopterus longiopes: an uplifting example of growth form change.

The leaves of Cymopterus longipes form prostrate rosettes early in the spring. As the weather warms, these leaves are elevated on a pseudoscape (false stem) which develops below the rosette through the elongation of the caudex (in the region between root and shoot). The effect of this growth form change on the water relations and photosynthesis in C. longipes was investigated. Pseudoscape height was not linked to phenology or plant size. Leaf conductance, leaf temperature, and leaf water potential were notably similar between plants with different pseudoscape height growing in different microsites. Experimental manipulation of the microclimate around plants growing naturally allowed us to demonstrate that increased temperature led to an increase in the rate of pseudoscape elongation. By changing the distance above the ground surface of the rosettes of some plants we determined that leaf temperature, leaf to air vapour concentration deficits, leaf conductances, and leaf water potentials were all influenced by pseudoscape height. Leaf conductance in C. longipes had a strong negative relationship with ΔW. Since the temperature response of net photosynthesis was extremely flat it was concluded that pseudoscape elongation may be an important morphological means of increasing water use efficiency.