Well, my apologies all. Life and work have been very much getting in the way, so today’s entry will be one to belatedly conclude the series for UBC’s Celebrate Research Week.
Lindsay introduces today’s author:
Dr. Quentin Cronk is a Professor in Plant Science at UBC’s Biodiversity Research Centre where he works on flower evolution in legumes and the genetic factors that underly these morphological changes. Together with his PhD student Isidro Ojeda they have investigated the distribution of epidermal types in petals of legumes and how this feature has evolved within the family.
Dr. Cronk writes:
The first picture (A) depicts the distribution of the epidermal types in a “papilionoid legume” with a typical pea-type flower, Lotus burtii. The second picture (B) depicts the same in a “caesalpinioid legume” with a caesalpinoid flower, Cassia roxburghii. The latter is thought to be a more primitive flower type. The epidermal photographs were taken using a scanning electron microscope (SEM) of fresh petals that were put directly into the microscope.
Pea-flowers, exemplified here by Lotus burttii, have three distinctive types of petals, one upper (dorsal), two side (lateral) and two lower (ventral) petals. Each petal type has a different role during the flower-pollinator interaction. For instance, due to its position within the flower, the upper petal is highly visible and acts to attract pollinators, while the side petals in papilionoid flowers are mostly used as landing platforms for bees.
Ojeda and Cronk found, in a survey of 175 species, that most pea-flower types have the distribution of epidermal types depicted in figure A. Each petal type has a specific surface structure that gives each petal its own unique identity. For instance the bumpy surface of the upper petal reflects light in a way that makes the petal brighter and more attractive to bees.
In contrast, legumes with a caesalpinoid-type flower do not have this diversification of epidermal types within the flower. The different types of petals cannot be differentiated at the epidermal level. This also applies in the redbud (Cercis canadensis), which has a flower that looks like a pea-type flower, but in fact it is a caesalpinioid legume, and the petal surfaces confirm this.
This survey has allowed the identification of major epidermal types and the general trends of its evolution within the family. Furthermore, it allows us to study the link between the underlying genetic controls (petal identity genes) and petal morphology. We are applying this to understand the evolution of related legume species with very different flower types, for instance in the transition from bee to bird pollination, as described in a previous UBC Research Week.
This broad survey would not have been possible without the living plant collections of botanical gardens. For this study we used the collections of the UBC Botanical Garden, the Fairchild Tropical Botanical Garden in Florida, USA and the Jardín Botánico Regional at CICY, Mexico.
For more details of this work, please see the published paper: Ojeda et al. 2009. Evolution of petal epidermal micromorphology in Leguminosae and its use as a marker of petal identity. Annals of Botany 104(6):1099-1110. doi:10.1093/aob/mcp211.