Leaf window, also known as epidermal window, and fenestration, is a specialized

leaf A leaf (: leaves) is a principal appendage of the plant stem, stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leav ...

structure consisting of a translucent area through which light can enter the interior surfaces of the leaf where

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

can occur. The translucent structure may include epidermal tissue, and in some succulent plants it consists of several cell layers of

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

, which may also function as water-storage tissue. It can appear as a large continuous patch, a variegated or reticulated region, or as numerous small spots. It is found in some

succulent plant In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meanin ...

s native to arid climates, allowing much of the plant to remain beneath the soil surface where it is protected from desiccation by winds and heat while optimizing light absorption. Many species featuring leaf windows are native to Southern Africa.

Functions

The primary function of the translucent windows is to increase the absorption of

radiant energy In physics, and in particular as measured by radiometry, radiant energy is the energy of electromagnetic radiation, electromagnetic and gravitational radiation. As energy, its SI unit is the joule (J). The quantity of radiant energy may be calcul ...

, and thereby the rate of photosynthesis. Epidermal windows are commonly situated at the apex of leaves, allowing light to be captured and utilized even when the plant is almost entirely below the soil surface, minimizing exposure of leaf surface area to

desiccation Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. The ...

by intense heat. The windows focus and channel diffused light to the green photosynthesizing surface hidden inside the underground part of the plant. An absence of

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

ta in the translucent tissue prevents water loss. It has been found in the ''

Lithops ''Lithops'' is a genus of succulent plants in the ice plant family, Aizoaceae. Members of the genus are native to southern Africa. They avoid being eaten by herbivores with their camouflage as small stones, and are often known as pebble plants ...

'' species of succulents that leaf window size correlates inversely with habitat

solar irradiance Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ( ...

; plants growing in regions of high irradiance and low rainfall have smaller windows than those growing in cloudy, high-rainfall regions. The carnivorous cobra lily (''Darlingtonia californica'') uses fenestration to confuse insects and increase the effectiveness of its trap.

Species

Genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

of plants with numerous species having translucent epidermal windows include: *'' Bulbine'' spp. (B. haworthioides, B. mesembryanthemoides, etc.) *'' Conophytum'' spp. *'' Callisia'' spp. ( ''C. navicularis'', etc.) *''

Fenestraria ''Fenestraria'' (known as babies' toes) is a (possibly monotypic) genus of succulent plants in the family Aizoaceae, native to the Namaqualand in Namibia. Description The only species currently recognised in this genus is ''Fenestraria rh ...

'' spp. *'' Frithia'' spp. *''

Haworthia ''Haworthia'' is a large genus of small succulent plants endemic to Southern Africa (Mozambique, Namibia, Lesotho, Eswatini and South Africa). Like aloes and gasteria they are members of the Family (biology), subfamily Asphodeloideae and they ...

'' spp. *'' Haworthiopsis'' spp. ('' H. koelmaniorum'', '' H. tessellata'', etc.) *''

'' spp. *'' Pleiospilos'' spp. (Questionable) *'' Peperomia'' spp.: notably '' P. columella'' and '' P. nivalis'' *''

Sarracenia ''Sarracenia'' ( or ) is a genus comprising 8 to 11 species of North American pitcher plants, commonly called trumpet pitchers. The genus belongs to the family Sarraceniaceae, which also contain the closely allied genera '' Darlingtonia'' and '' ...

'' spp. Several other plant species have epidermal windows: *'' Cephalotus follicularis'' *''

Darlingtonia californica ''Darlingtonia californica'' —also called the California pitcher plant, the Oregon pitcher plant, cobra lily or cobra plant—is a species of carnivorous plant in the new world pitcher plant family, Sarraceniaceae. It is the sole species wit ...

'' *'' Senecio rowleyanus'' Plants with leaf windows are sometimes known as ''window plants'', though this is also the

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

used to refer to ''Fenestraria rhopalophylla''.

References

{{Reflist Leaves Plant morphology

Functions

Species

See also

References