OF THE WEEK
Dr. T. Ombrello - UCC Biology Department
Living Stones, Stoneface, Pebble Plants, Flowering Stones, Mimicry Plant
Scientific name: Lithops species
of scientific name:
- from the Greek “lithos” meaning stone and “ops” meaning face.
A pot of Living Stone plants growing in one of Union County College's greenhouses.
37 species of the plant genus Lithops
are the most well known members of the group of succulent plants commonly
referred to as Living Stones. Native
only to the deserts of South Africa, these small curious plants escaped
detection by botanists until 1811 when Thomas Burchell, a European traveler,
discovered one by accident. In his
1822 book entitled Travels in the Interior of Southern Africa,
Burchell described his discovery as follows:
“On picking up from the stony ground what I supposed was a
curiously shaped pebble, it proved to be a plant . . . . but in color and
appearance bore the closest resemblance to the stones between which it was
Stones are perennials, often found growing in clumps although individual plants
usually consist of just 2 very succulent leaves. The paired leaves are united and together are shaped like an
inverted cone. The stem is
practically non-existent, and the roots seem to arise from the base of the
leaves. From the fissure across the
top of the united leaves arises either flowers or a new pair of leaves to
replace the older ones. The
delicate growing point is safely hidden beneath the soil between the leaves near
nature, only the tops of the leaves are exposed above the soil surface.
When cultivated under other than desert conditions, Lithops
do best when the leaves are left well above the soil surface.
most of the plant’s leaf surface below the ground has certain advantages.
It is cooler; there is less exposure to drying winds, and less chance of
being spotted by a grazing animal (although no animals are known to use Living
Stones as food). Even gas exchange occurs underground. The pores (stomates) open without any exposure to wind or
sun, so water loss is minimized during this process.
disadvantage, however, is the limited amount of leaf surface area exposed to the
sun for photosynthesis to supply food for the plant.
The Living Stones demonstrate an interesting evolutionary adaptation to
overcome this light problem; their leaves have transparent “windows”.
In fact, they are the most advanced “windows” of all succulent
plants. The clear tips of the
leaves have a crude optical system that permits light striking the windows to be
diffused by crystals of calcium oxalate onto the green photosynthetic area
below. So, with a minimum of
exposure to the outside environment, a maximum area of photosynthetic tissue can
survival feature built into the Living Stones involves seed dispersal and
longevity. Since water is essential
for germination, but quite rare in their habitat, seed capsules will not open to
disperse their long-lived seeds until they experience rainfall or heavy dew.
Sometimes the seeds are retained for many months.
This ensures that the dispersed seeds have sufficient moisture to begin
the next generation.
these adaptations contribute to the Living Stones’ ability to thrive in
habitats with 120oF temperatures, full sun, and minimal rainfall.
Stones are also masters of mimicry. The
circular or oval tips of the leaves resemble weathered stones on the soil
surface. Each species harmonizes to
some extent with its native background, and can be found only in habitats that
provide the right colors and textures. For
example, where several rock formations occur side by side, Lithops
species are confined to places where they blend best with the background. The colors of leaf tips range from plain gray to brown,
with some species showing intricately mottled patterns.
Just why they have evolved to mimic their habitat is quite puzzling, in
light of the aforementioned statement on their undesirability as food for
animals. Mimicry is abandoned,
however, when the Living Stones flower. Their
large, showy, white or yellow colored blossoms are quite conspicuous.
This is not surprising, since they are insect pollinated and, therefore,
must be attractive to potential pollinators.