Morphological and Anatomical Adaptations to Light Conditions
Light is one of the key abiotic factors determining plant growth, development and productivity. It serves not only as an energy source for photosynthesis but also as a crucial signal regulating morphogenesis (Strasburger, 1971; Khan et al., 2025). In natural and agricultural ecosystems, light conditions are extremely heterogeneous: the upper layers receive excessive solar radiation, while the lower layers and the soil surface experience deep deficiency (Novichonok et al., 2018; Ghorbel et al., 2023). Moreover, within the crown of a single tree, leaves may simultaneously be exposed to direct illumination (“sun leaves”) and deep shade (“shade leaves”) (Dörken & Lepetit, 2018).
Under these conditions, plants develop a set of hereditarily fixed and modification adaptations aimed at optimising light capture and protecting the photosynthetic apparatus from damage. This set is commonly called morphological and anatomical adaptations to light conditions (or photomorphogenetic adaptations).
In a broad sense, this concept covers all levels of plant organisation: from changing the spatial arrangement of leaves (leaf mosaic, shoot architecture) to reorganisation of the internal structure of the leaf (mesophyll type, epidermal structure) and even subcellular changes (chloroplast structure, development of vascular tissues) (Beck, 2010; Evert, 2006). In the figurative expression of botanists, the plant “tunes” its vegetative organs like a receiving antenna to capture photosynthetically active radiation (PAR) as efficiently as possible, or, conversely, to dissipate excess energy and prevent photoinhibition.
The main essence of adaptations is that the form and internal structure of plants are not random, but represent the result of long evolution under the action of natural selection (Meyen, 1978; Givnish, 1978). For agricultural science, understanding these mechanisms is extremely important because it allows managing sowing density, shaping fruit tree crowns and selecting varieties for intensive lighting in greenhouses and vertical farms.
Key concepts to be discussed in the article:
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Ecological groups of plants in relation to light: heliophytes, sciophytes and facultative heliophytes (shade‑tolerant) (Serebryakova et al., 2006).
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Leaf mosaic — spatial arrangement of leaves to reduce mutual shading (Strasburger, 1971).
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Sun leaf and shade leaf — modifications of leaves of the same plant depending on illumination within the crown (Dörken & Lepetit, 2018).
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Xeromorphic and hygromorphic traits — features similar to adaptations to dryness or humidity that appear in sun and shade leaves respectively (Serebryakova et al., 2006).
Below we will systematically analyse how the external and internal structure of plants adapted to different light conditions differ, and how this knowledge is applied in modern crop production.
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q::What ecological groups of plants are distinguished in relation to light? Heliophytes (light‑loving), sciophytes (shade‑loving) and facultative heliophytes (shade‑tolerant). Heliophytes grow in open places, sciophytes in forest shade, shade‑tolerant plants adapt to different conditions.[answer-1]
q::How do sun leaves differ from shade leaves on the same plant? Sun leaves are small, thick, with well‑developed palisade tissue, high stomatal density and thick cuticle. Shade leaves are large, thin, with well‑developed spongy tissue and low stomatal density.[answer-2]
q::What is leaf mosaic and why is it needed? Leaf mosaic is the arrangement of leaves on a shoot with minimal mutual shading. It allows the plant to capture diffuse light more efficiently, especially in the lower forest layers.[answer-3]
q::How does knowledge of light adaptations help an agronomist? It allows selecting sowing density, shaping fruit tree crowns, choosing crops for multi‑layer cultivation and managing light conditions in greenhouses to increase yields.[answer-4]
q::Why do plants in bright light often have small, pubescent leaves? Small size and dense pubescence reduce overheating and water loss, and also protect against ultraviolet radiation. These are adaptations of heliophytes to excessive insolation.[answer-5]
