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.

本研究从旁遮普地区生态迥异的多个区域采集了15个牛角瓜（Calotropis procera (Aiton) W.T. Aiton，又名马利筋（milkweed））种群，旨在解析该植物在异质环境中维持生态优势的相关解剖学性状。该植物茎与叶的结构特征呈现表型变异：沙漠种群旱生性特征显著，兼具厚角质层与表面被毛，其茎、叶内的木质部导管、韧皮部面积及贮藏薄壁组织（皮层与髓）的沉积量均有所提升；盐渍生境种群的内部韧皮部面积与茎部被毛量有所增加，其叶片的厚度与木质部导管则显著增大；山地种群的茎面积、外部韧皮部面积、角质层厚度及表皮细胞面积均为所有种群中最高；河岸种群则具备若干突出特征：厚壁组织纤维束膨大，中脉厚度、角质层厚度与内部韧皮部面积均有所提升；人工林种群的表皮下发育有显著的厚角组织层，叶片厚实且木质部导管增宽；路边种群的叶片具厚角质层与膨大的木质部导管，此外其茎表面的毛状体占比极高。叶片肉质化是适应沙漠与干旱山地种群的典型特征。上述所有特征或可助力牛角瓜在多种生境中实现适应性生存，涵盖沙漠与半荒漠、盐渍生境、干旱山地、河流/运河岸、路边及人工林等多种生境。