Adaptive strategies for ecological fitness in Calotropis procera (Aiton) W. T. Aiton
Fifteen populations of Calotropis procera (Aiton) W.T. Aiton (milkweed) were collected from ecologically different regions of Punjab to evaluate anatomical traits that contribute to the ecological success of this plant in heterogeneous environmental regimes. Structural features relating to stems and leaves showed phenotypic variation. Xeromorphy was high in the desert population possessing thick cuticle and surface hairiness, enhanced xylem vessels, phloem area and deposition of storage parenchymatous tissues (cortex and pith) in the stem and leaves. The population from salt-affected areas showed increased inner phloem area and pubescence in stems, whereas lamina thickness and xylem vessels were greatly enlarged in leaves. The population from mountainous ranges showed the maximum stem area, outer phloem area, cuticle thickness and epidermal cell area. The population along riverbanks showed some prominent features like enlarged bundles of sclerenchyma fibers, and enhanced midrib thickness, cuticle thickness and inner phloem area. The population from the artificial forest plantation had a prominent layer of collenchyma developed under the epidermis, thick lamina and widened xylem vessels. The population from roadsides possessed thick cuticles and enlarged xylem vessels in leaves; in addition, a great proportion of trichomes/hairiness was found on the stem surface. Leaf succulence was the prominent feature of the population adapted to desert and dry mountains. All of these features possibly contribute to C. procera adaptability in a variety of habitats, i.e., desert and semi-desert, salt-affected areas, dry mountains, river/canal banks, roadside and forest plantations, and others.