A quantitative analysis of leaf growth parameters in Myriophyllum aquaticum (Haloragaceae)

This quantitative developmental study examines various parameters associated with the growth of leaves of Myriophyllum aquaticum (Vell.) Verdc. on different shoot systems from a single clonal plant to determine the dynamics of growth processes during the development of a normal, typical leaf. Early stages of development, representing the morphogenetic phase of leaf formation, were used to document the growth rate of leaves, the dynamics of leaf lobe formation, the location of initiation of leaf lobes, and allometric relationship between leaves and leaf lobes. Even though there were variations in maximum leaf length between shoot systems, similar growth patterns were observed. In addition, during the exponential phase of growth, the location of initiation of those lobes was constant in each shoot system. There was a positive correlation between the rate of growth of leaves and the rhythm of initiation of lobes resulting in the formation of strikingly similar leaf morphologies regardless of whether the leaf is long with more lobes or short with fewer lobes. An allometric relationship between leaf length and the length of its lobes was observed. To our knowledge, this has never been noted in a system like this. The existence of constant parameters of growth is essential to maintain some degree of consistency but variations in the modalities of those parameters allow for flexibility within the system. For example, the interplay between rates of leaf growth and duration of growth can explain the range of maximum leaf length observed or can be viewed as a way of using different means to achieve similar end products (fast rate of growth and short duration versus slower rate of growth and longer duration).