A multiple epidermis or a periderm in Parkinsonia praecox (Fabaceae)

Abstract

A multiple epidermis in the green stems of Parkinsonia species has been described; however, there are disagreements amongauthors with regard to origin and tissues involved. The aims of this study were to identify the origin and development of the epidermisand cortex of P. praecox and relate these to possible adaptations to arid environments. Samples from new branches, to the stem, wereremoved and prepared using two embedding techniques. Our results show that the epidermis is simple, but periclinal divisions start farfrom the apical meristem. The inner derivatives maintained periclinal and anticlinal divisions, which are interpreted as meristematic,promoting continuous cell renewal. Wax and cutin deposits suggest that a special epidermis is present; however, it does not correspondto a multiple one. The cortex has four distinct regions. As the branch circumference increases, modifications occur in the first, second,and fourth regions, and sclerenchyma with abundant prismatic crystals develops. The third region maintains its identity with abundantchloroplasts. The occurrence of crystals and chlorenchyma improves structural stiffness, increases the reflectivity of plant surfaces, andfacilitates the recycling of respiratory CO2. Abundant waxes, chlorenchyma, sclerenchyma, and crystals in the stems may be adaptationsof P. praecox to xeric environments.