• Fenestra = Window in Latin language.
• Fenestration = The area in which the fenestra occurs.
   

Left: Two windowed (fenestrated) plants (Haworthia and Lithops) with their translucent tissues.

Photo 1: windowed reticulated leaves of Haworthia emelyae
 v. comptoniana

photo 2: A longitudinal section  showing the transparent tissues.

Windowed growth habit of some subterranean leaf succulents.

A number of South African succulents like Lithops ssp. and Haworthia ssp. (See: photo 1 and 2 ) to escape the killing heat of the desert grow almost entirely subterranean and have evolved special fenestrate (windowed) leaves that grow below the surface of the soil; This succulent  leaves have a nearly transparent flat apex exposed to the atmosphere and are even at the soil level. This permit the plants to minimize the heating effects of high light intensity and to reduce the drying effects of desert air during prolonged drought. There are no stomata in the windows, so little water is lost, these plants remain subterranean because they have contractile roots which continually pull the plants deeper into the ground as the stem elongates.

The disadvantage, however, is the limited amount of leaf surface area exposed to the sun for photosynthesis to supply food for the plant but the translucent window in the top surface, however, the fenestration allow sunlight to be captured and utilized even when the plant are retracted below the surface of the soil. This is an interesting evolutionary adaptation to overcome this light problem; their leaves are a simple optical system that permits light striking the windows to be diffused onto the green, photosynthesizing surface situated underground. So, with a minimum of exposure to the outside environment, a maximum area of photosynthetic tissue is ensured.


           

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