The Swiss Cheese Plant

By Director Lew Feldman

Perhaps one of the most unusual modifications in leaf design occurs in the genus Monstera, more commonly known as the Swiss cheese plant or cut-leaf Philodendron. These plants develop holes and splits in their leaves, a process scientifically termed fenestration (from the French word for window, fenêtre).

Monstera adansonia

Hypothesized Functions of Fenestration
In their native habitat these vines can climb to significant heights by attaching their roots to the trunks and stems of tall-growing plants. With regard to the function of the holes or splits, it is hypothesized that it is an adaptation to this elevated, tree-top location.

For instance, in this scenario, the tree-top location of this plant exposes it to high velocity, potentially damaging winds. Thus, the role of the holes or splits, in part, is suggested to diffuse and redirect the force of the wind.

Additional suggestions as to the function of these leaf modifications include,

• Rain Passage: They may allow rain to pass through to the underlying roots more easily.
• Light Penetration: As the plant climbs, the “windows” may allow light to penetrate to lower leaves, ensuring they receive adequate light.
• Insect Discouragement: An unproven, yet intriguing, suggestion is that the holes trick or discourage insect predation. An insect might view the fenestrated leaf as already “damaged” and thus an unfavorable location to deposit eggs, whose larvae would otherwise consume the leaf.

How Fenestration Forms
While the exact function of these leaf modifications is still unclear, we know much about how they form. The holes appear when the developing leaf is still quite small (less than 1-2 mm in height), as shown below.
The holes form through Programmed Cell Death (PCD), where specific cells within the developing leaf die, leaving a small space that enlarges into the hole or split as the leaf grows.

However, the mechanism underlying the patterning or distribution of the holes—why certain cells are fated to die while others are not—remains largely unknown.

Scanning Electron Microscope view of developing holes in the leaves of Monstera sp., as a result of Programmed Cell Death (from Kaplan, 1984).

Another striking example of fenestration due to programmed cell death is shown by the water plant, Aponogeton, a common aquarium plant, pictured below.

Aponogeton madagascariensis, a common aquarium aquatic plant.