- Living Stones
- Pebble Plants
- Flowering Stones
Lithops are a genus of succulents that resemble a pebble or a rock. They are natively found in dry, arid climates such as southern Africa. Generally, a single lithops lacks a stem and has only two large succulent leaves fused together at a central seam.
Lithops are a perennial plant so they grow a new set of leaves every year. The meristem (area of active, new growth) is located within the main seam. As the plant grows, two new leaves will develop and enlarge within this seam which eventually splits the plant open. Nutrients are moved into the new leaves from the old leaves (the old leaves will dry up and die).
The most unusual thing about the plant is that chlorophyll is only located on the inner surface of the leaves. To allow light inside of the leaf, the top surface of the plant is translucent (leaf “window”). These “windows” can be large and continuous or small and divided by spots or lines depending on the exact species. Image “A” shows this physiology in a cross section of a typical lithops.
The structure of lithops gives an insight into the ruthless environment it grows natively. Being a desert plant, water is conserved by having a simple anatomy with only two leaves and a single tap root. As seen by the cross section in image A, the majority of the plant is devoted to water storage and the plant is overall small and grows very close to the ground to minimize heat effects.
The leaf-window mechanism gives the plant an advantage because chlorophyll does not need to be located on the outside of the plant. The majority of the plant can remain underground where it is cool and sunlight entering through the top window can be used within the plant.
For other example species on campus which utilize the leaf-window mechanism see:
Fenestraria spp. (Ex. “Babies Toes”)
Haworthia spp. (Ex. “Zebra Plant”)
Sources:http://www.cactus-art.biz/note-book/Dictionary/aaa_Dictionary_pictures/translucent_fenestrate_haworthia_and_lithops.jpg (Cross section image prior to modification) http://www.llifle.com/photos/Lithops_olivacea_C109_10_km_N_of_Pofadder,_South_Africa_12609_l.jpg http://media-cache-ak0.pinimg.com/236x/b8/1d/68/b81d6842fe44288485d9716398735830.jpg http://en.wikipedia.org/wiki/Leaf_window http://en.wikipedia.org/wiki/Lithops