Category: 3. Modified Leaves

These plants are always attention grabbers and have intrigued folks for centuries. Plants that trap insects usually occur in swampy areas and bogs of tropical and temperate regions. Generally, the soil is lacking some vital ingredient for life and the plants utilize trapped insects and small organisms to fill the gap. The captured prizes are dissolved and absorbed by the plant. However, if insects are not available (i.e. a laboratory situation) the plants will develop if nutrients are given instead. The following four plants represent the four main mechanisms of capture.

• Pitcher Plants—drowning trap
• Sundews—sticky trap
• Venus Flytraps—hinged trap
• Bladderworts—underwater trapdoor trap

Bracts are found at the bases of flowers and are sometimes mistaken as petals. They compensate for small flowers or absent petals. The poinsettia ‘flower’ is really composed of bracts. The center cluster of tiny flowers is the main event, while the bracts do all the attracting.

Walking fern leaves produce new plants at their tips. Air plants, a succulent, have little notches along their leaf margins where new plants are produced with leaves and roots of their own. The baby plants will produce even if the parent leaf is separated from the rest of the plant.

There are at least three members of the Carpetweed family in the Kalahari desert with unique adaptations to the sandy growing environment. These plants have leaves shaped like ice cream cones. The leaves are buried in the sand, leaving the transparent dime-sized tip of the leaf exposed at the surface. The transparent surface is covered with a thick epidermis and cuticle and has virtually no stomata. This arrangement allows light nearly direct access to the mesophyll with chloroplasts inside. The plant, for the most part, is buried and away from drying winds and abrasive blowing sands. There are other examples of succulent plants with window leaves.

the leaves of some plants, such as the Dischidia plant from tropical Australasia, develop odd pouches that become the symbiotic homes of ant colonies. The colonies carry in soil particles and add nitrogenous wastes, which the leaves collect moisture through the condensation of water vapor via the stomata. The area is a rich medium for the adventitious roots that grow down into the soil contained in the pouch—hence the flower pot function of the modified leaf.

Succulent leaves are leaves modified to retain and store water. Water storage is permitted because of the thin-walled, non-chloroplast parenchyma cells just beneath the epidermis and to the interior of the chlorenchyma tissue. The vacuoles in the non-photosynthetic cells store the extra water resources. There are plants with succulent leaves that have a special photosynthetic process. We will look at these in a later tutorial. The fleshy leaves of onions and lily bulbs store large amounts of carbohydrates which are utilized by the plant in the next growing season.

Desert plants have leaves modified as spines. Water loss is correlated to the surface area, so the decrease in leaf surface area consequently decreases water loss to the outside. In plants with spines, photosynthesis is generally conducted by the stem tissue. The tissue is made of sclerenchyma cells and replaces any ‘normal’ leaf tissues. The modifications arising in the axils of leaves are stem modifications, not leaf spines, but thorns. Recall, that the prickles of roses and raspberries are not leaves or stems, but outgrowths of the epidermal or cortex just beneath the prickle.

Many plants have modified leaf structures called tendrils that aid in climbing or supporting the plant’s weight. Tendrils are very sensitive to contact and can be readily redirected based on touch and solid contact. Tendrils become coiled like springs and when contact with a support structure is made, the tip not only coils around it but the tip direction reverses. It needs to be noted that not all tendrils are modified leaves, tendrils of the grapevine, for example, are modified extensions of the stem tissue.

In growing environments with extremely arid conditions, the plants will generally have thicker more leathery leaves. Their stomata are usually reduced in number and are sunken into the leaf surface in special depressions. Some may have succulent leaves or no leaves at all—where the stem takes over photosynthetic responsibilities—or they may have dense hairy coverings. In areas where the soil freezes and water resources are limited, pine trees may have modifications similar to desert plants. Including sunken stomata, thicker cuticle, and hypodermis (thick-walled cells) beneath the epidermis. The compass plant is a unique example of growth set up directionally—East and West—in order to reduce moisture loss.

Depending on the conditions where a particular plant lives, it may or may not require some specialized adaptations in order to accommodate various environmental factors: humidity, temperature, light, water, and soil conditions for example. We will look briefly at ten types of specialized leaves. I would suggest further research if you are interested in more detail.

Shade leaves

In some plants, leaves with barely noticeable or unnoticeable modifications will occur right alongside those that are unmodified. Leaves in the shade tens to be thinner and have fewer hairs than those on the same tree exposed to direct light. In addition, they are generally larger and have less defined mesophyll layers and reduced numbers of chloroplasts than their better lit counterparts.