Heliophytes and Sciophytes

Heliophytes and Sciophytes

Not every classification of plants by habitat is based on water. Heliophytes and sciophytes are grouped instead by their response to light — specifically, by how much direct sunlight they require in order to grow and photosynthesise well.

Heliophytes are sun-loving plants that grow and thrive best when exposed to full, direct sunlight; they typically do not perform well, or fail to grow at all, in shaded conditions. Structurally, heliophytes tend to have relatively small, thick leaves, an adaptation that helps them cope with the higher light intensity, heat, and associated water loss that come with an open, sun-exposed habitat. Their leaves are usually well supplied with palisade tissue, often in more than one layer, which allows them to make efficient use of the abundant light available and to sustain a high rate of photosynthesis under strong illumination. A familiar local example of a heliophyte is Tridax procumbens, a common weed that grows vigorously in open, fully sunlit ground such as roadsides, waste land, and open fields, and is rarely found thriving in shaded spots.

Sciophytes, in contrast, are shade-loving plants that are adapted to grow well under low light conditions, such as the understorey of a forest or a shaded garden corner, where the intensity of sunlight reaching the plant is much reduced. To compensate for this reduced light supply, sciophytes typically develop leaves that are larger and thinner than those of heliophytes, increasing the surface area available to intercept whatever light does filter through, and their mesophyll tissue is generally richer in chlorophyll, allowing the plant to photosynthesise efficiently even in dim conditions. A familiar local example of a sciophyte is a fern such as Adiantum (maidenhair fern), which is commonly found growing in shaded, moist spots such as the base of walls, under tree cover, or in shaded garden beds, and which typically fails to thrive if placed in strong, direct sunlight. …