The evolution and functional significance of leaf shape in the angiosperms

Abstract

Abstract. Angiosperm leaves manifest a remarkable diversity of shapes that range from developmental sequences within a shoot and within crown response to microenvironment to variation among species within and between communities and among orders or families. It is generally assumed that because photosynthetic leaves are critical to plant growth and survival, variation in their shape reflects natural selection operating on function. Several non-mutually exclusive theories have been proposed to explain leaf shape diversity. These include: thermoregulation of leaves especially in arid and hot environments, hydraulic constraints, patterns of leaf expansion in deciduous species, biomechanical constraints, adaptations to avoid herbivory, adaptations to optimise light interception and even that leaf shape variation is a response to selection on flower form. However, the relative importance, or likelihood, of each of these factors is unclear. Here we review the evolutionary context of leaf shape diversification, discuss the proximal mechanisms that generate the diversity in extant systems, and consider the evidence for each the above hypotheses in the context of the functional significance of leaf shape. The synthesis of these broad ranging areas helps to identify points of conceptual convergence for ongoing discussion and integrated directions for future research.

Genetic analysis of an ephemeral intraspecific hybrid zone in the hypervariable tree, Metrosideros polymorpha, on Hawai‘i Island

“…glaberrima, heritabilities were substantial (h 2 = 0.31 to h 2 = 0.85). This might be unexpected, given the anticipated significance of leaf traits for fitness (Nicotra et al, 2011) and the contrasting directional selection imposed on juveniles of these forms in their parental habitats (Fisher, 1930). The maintenance of heritable variation within varieties may be explained by their history of recurring, prolonged episodes of introgression on intermediate-aged lava flows that may facilitate adaptation to changing environments (Grant and Grant, 1994;Seehausen, 2004).…”

“…incana and glaberrima differ in the genetic architecture of simple leaf traits that may reflect their contrasting home environments (Nicotra et al, 2011) as well as differences in the varieties' ecological breadths. The contrasts in leaf shape between these varieties may reflect tradeoffs between structure and function experienced in earlyand late-seral forests.…”

Leaf morphology of progenies in Q. suber, Q. ilex, and their hybrids using multivariate and geometric morphometric analysis

“…Leaf morphology of progenies in Q. suber, Q. ilex, and their hybrids bifacial leaves (Nicotra et al 2011). Possibly, disruptions of regulatory networks due to interspecific genomic incompatibilities are responsible for producing abnormal phenotypes in Q. ilex × Q. suber progenies.…”

Review: Improving the Impact of Plant Science on Urban Planning and Design

“…Light interception is affected by the canopy architecture (the sum of all the plants in field or all the leaves on a plant, depending on scale). Light interception is in balance with a number of other factors in the plant, such as water availability, gas exchange, and herbivory [47][48][49], and therefore leaves can be seen as adapted to environments that include light, rather than optimised for light interception. Eighty-five per cent of raw light interception efficiency in plants is determined by two variables; crown density (ratio of leaf area to total crown surface area) and leaf dispersion (the total aggregation of leaves).…”