However, in case of leaf shape, environmental influences viz. Moreover, smaller-sized leaves are better adapted to hot or dry environments. In the case of leaf size, the explanation has been straightforward it decreases with increasing altitude, decreasing rainfall, and soil nutrient content. This variation, arising due to several factors, offers great functional significance that influences plant success. But their attractiveness lies in their varying shapes and sizes from the uncommon butterfly-shaped leaf of Christia obcordata to the extensively studied ovate-shaped leaf of Arabidopsis thaliana (Figure 1A and B). In comparison to the vibrant colors of the flower, the ‘leaf’ has nothing special to offer as most are green-colored attributed to the presence of chlorophyll. In hindsight, formation of the pitcher tube in Nepenthes might involve the recruitment of similar genetic mechanisms that occur during sympetaly in Petunia. the pitchers of the carnivorous plant Nepenthes which have evolved to provide additional support to the plant survival in its nutrient-deficient habitat. This immense amount of information available will serve as the basis for studying and understanding innovative leaf morphologies viz. In addition to genetic control, environmental factors also play an important role during the final adjustment of leaf shape. We found that the underlying factors governing these processes are inherently genetic: PIN1 and KNOX1 are indicators of leaf initiation, HD-ZIPIII, KANADI, and YABBY specify leaf outgrowth while ANGUSTIFOLIA3 and GROWTH-REGULATING FACTOR5 control leaf expansion and maturation besides, recent research has identified new players such as APUM23, known to specify leaf polarity. Here, we review these studies and discuss the various factors that contributed towards shaping the leaf initiated as a small bulge on the periphery of the shoot apical meristem (SAM) followed by asymmetric outgrowth, expansion and maturation until final shape is achieved. This has fascinated scientists worldwide, and research has progressed tremendously in understanding the concept of leaf shape determination. During the course of evolution, the megaphylls have attained complexity not only in size or venation patterns but also in shape. Significant contributions have come from megaphyllous leaves, characterized usually as flat, thin lamina entrenched with photosynthetic organelles and stomata, which serve as the basis of primary productivity. The independent origin and evolution of leaves as small, simple microphylls or larger, more complex megaphylls in plants has shaped and influenced the natural composition of the environment.
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