Koukol*, Scott R., Biological Sciences, California State Polytechnic University, Pomona, 91768
The ecophysiology of the genus Encelia (Asteraceae: Heliantheae) as a predictor of internal anatomy
Encelia is a genus of drought tolerant shrubs and subshrubs that are generally found in arid to semi-arid areas of southwestern North America and western South America. This study includes three species: Encelia californica, E. farinosa and E. frutescens, each with a different ecophysiological strategy for surviving aridity. E. californica occurs in coastal regions where humidity is higher and summers are cooler. E. farinosa and E. frutescens are found in desert regions, with E. farinosa occurring on hillsides and E. frutescens in river beds. Each of these species deals with heat and water stress in a different way: E. californica is deciduous, E. farinosa relies on pubescence and E. frutescens on transpirational cooling. The various environmental conditions may have resulted in structural adaptations in the internal anatomy of each species. E. californica may have thinner leaves that require less energy to produce, E. farinosa may have fewer stomata, a thicker epidermis and a smaller percentage of tissues consisting of primary growth due to the slower growth rate, and E. frutescens may have more stomata, more or larger vascular tissue, and a larger percentage of tissues consisting of primary growth due to faster root growth necessary in keeping constant contact with water to maintain a higher transpiration rate.