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Why do some Plants have Dark green leaves?

Dark green leaves

Dark green leaves. Almost all plants contain green leaves and many of them have dark green leaves. Leaves are of various types, shapes, sizes, and colors. Grass, needle-shape pine leaves, fronds in ferns, bracts on a poinsettia, and spines in cactus may not appear like typical leaves; because they are modified by plants to suit their surroundings. Varied colors of the leaves can be attributed to a chemical compound called Pigment. Pigment absorbs certain colors in the sunlight and reflects the others. The reflected colors are visible to our eyes.

Significance of Color

The green pigment in the plants is called Chlorophyll. It is responsible for absorbing sunlight needed for food preparation in plants. There are also other “accessory pigments” – that give red, orange and yellow colors. Chlorophyll is of many types – A, B, C1, C2, D and F. Chlorophyll A is predominant in photosynthesis. While, Chlorophyll A absorbs short wavelengths – blue and violet colors in sunlight and reflects greenish-yellow, Chlorophyll B absorbs the long wavelength – red-blue region and reflects dark-green. It is an adaptive light-harvesting accessory pigment – absorbs maximum available light in shady areas and transfers it to Chlorophyll A. Green is reflected by both, but the ratio of Chlorophyll a-b varies across plants, giving the plants its different hues.

Structure of a chlorophyll

Environment

Tropical Rainforest has a canopy of trees. Lower plants, shrubs, lower branches of trees fight with each other for sunlight. They need to absorb whatever light is filtering through the canopy. So, Chlorophyll B is produced more in these leaves. Only with its help, Chlorophyll A can carry out photosynthesis. Hence these leaves are dark green in color. E.g. Rubber tree. They have broad, evergreen leaves. When grown in a garden, they can survive only in indirect sunlight or shade.

Sunlight

Similarly, plants growing under shade or indoors are likely to have dark green leaves. Shrubs under trees, lower branches of plants, houseplants are some examples. They either grow towards the light source or they modify their leaves to produce more chlorophyll b. You should not take an indoor plant in indirect sunlight rapidly. It should be gradually exposed to sunlight for better adaptability. E.g. Fern, Mint, Goldfish houseplant

Growth

Photosynthesis procedure inside a leaf

New leaves in a plant are small and light-green. As they mature, their functioning increases and chlorophyll is produced more and they get darker. Meanwhile, the old leaves covered by this new foliage, produce more chlorophyll b to capture light and they turn dark-green. In the absence of light, the plant stops producing chlorophyll and the old leaves wilt and fall down. Similarly, an upper surface of a leaf is darker than its lower surface. The upper surface is exposed to sunlight and produces more chlorophyll to aid in photosynthesis. Since the lower surface is hidden from sunlight, the plant conserves its energy by producing less chlorophyll. E.g. Fig tree

Weather Conditions

Some perennial and evergreen plants have to survive cold weather. While some plants become dormant, others adapt to the conditions by conserving their leaves. These plants produce more pigments and have dark green leaves to make use of whatever sunlight they can get. E.g. Evergreen plants like Fern, drought-tolerant plants like Blue Storm, perennials like Anemone Whirlwind, Cool-weather plant likes Spinach.

Dark green leaves

Hence, the darkness of the leaves depends on the above factors. Plants have the innate ability to adapt to any ecological conditions. Their varied structure, appearance, and growth is a reflection of this.

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