Living Stones: Lithops
Lithops are small, interesting plants from
southern Africa that are
relatively easy to grow indoors. The first Lithops was discovered by William John Burchell in 1811 during a botanical
expedition in southern Africa. During his travels in the Northern Cape Province, he found a strange looking brown
stone with a fissure across the surface near the town of Prieska. On closer inspection, this strange-looking stone
turned out to be a succulent plant. These plants, in the plant family Mesembryanthemaceae (Aizoaceae),
were named for their stone-like appearance: lithos (=stone) and opsis (=like).
Local Afrikaans names for these plants in areas where Lithops are known
include beeskloutjie
(cattle hoof), skaappootjie (sheep hoof) or perdeklou (horse's
hoof), for their resemblance to miniature hoofprints. In their native habitats in Namibia and South Africa,
Lithops have
evolved to blend in so well with their surroundings
looking just like the sand and stones they live among in shape, size and color
that they can be quite difficult to spot, even for those with a trained eye
and years of experience.
Lithops
(the word is both singular and plural) are found in arid regions in widely separated, sparsely
populated colonies. The average rainfall in areas where Lithops occur is generally less than 20", with most of the rain coming in spring and fall.
Some species occur in areas with an annual rainfall of 4" or less, and a few
rely on mist or fog as their main source of moisture. They are found growing in
many diverse habitats, on quartz grit or gravely flats, stony ridges and hills
of sand, decomposed granite, quartzite, shale, schist and limestone.
The vast majority of Lithops species occur in the Nama Karoo and
succulent Karoo and are especially common along the Orange River valley in the
Northern Cape that runs between Namibia and western South Africa.
Lithops are able to survive in
these dry areas because of their capacity to store
water, with almost the entire plant devoted to this function. Each
individual plant consists of two succulent leaves fused together
in the shape of an inverted cone (although some species will produce
multi-headed plants). The fissure at the top of the
plant is the division between the two leaves. There is no stem; the taproot
joins abruptly at the base of the leaves. The thick leaves can store enough
water for the plants to survive for months without rain. In periods of
drought (almost all the time) they shrivel and shrink below the soil level.
These small, nearly stemless succulents are partially subterranean. In
habitat the plants only grow from ½-1" high and from 1-3" wide, and they grow
flush with the ground. Staying small and keeping a low profile helps minimize
the effect of the intense heat and sunlight where they live. But this also
presents a problem of getting light to the photosynthetic apparatus of the leaf
cells (cholorophyll) that are underground. To solve this dilemma, the wide leaf
tips have windowed cells that allows light into the inner portion of the leaf,
where it is diffused before reaching the chlorophyll, which is scattered along
the interior leaf margins.
There are 36 species and numerous varieties (145+) of Lithops; all look quite similar to each other, differing mainly in the shape, markings, color and texture of the body.
They come in a variety of subtle colors of gray, brown, rust, green and pink.
There is considerable variation in the patterns of dots, lines or patches on the upper
surface that help them to mimic their surroundings. There may also be dimples or
indentations where the markings appear. The markings may heavily cover the leaf
surface, or the windows may cover most of the leaf surfaces.
Most
Lithops flower during autumn and early winter, producing daisy-like yellow,
pale orange or white
flowers. The flowers open in the afternoon of sunny days and close again in late
afternoon. The flowers emerge from the
fissure between the leaves. Some flowers
are scented. They range in size from roughly ½ to 1½", depending on the species
and conditions. Lithops are self-sterile, so
must be pollinated to produce seed. The seed is held inside a 4-8 chambered
fruiting capsule, which only opens when moistened, exposing the tiny seeds. In
nature, falling rain drops splash out the seeds to a distance of an inch to up to a
few feet from the parent plant. Once the capsule dries, it closes again,
protecting any seeds remaining until the next rain.
After the plant flowers, it goes into a period of dormancy during which at
least one new body develops. In the spring the
plants start to reabsorb the old leaves as the new ones develop.
Eventually the new body
pushes out from the fissure between the old leaves. The fissure of the new
leaves forms at about 90 degrees to the old fissure. Eventually, the old leaves
wither away to a dry, papery sheath on the side of the new body. Many plants will
also divide at this time, to produce more than one leaf pair so that a
single body gradually becomes a small cluster.
Cultivation of Lithops as Houseplants
Because they thrive in low humidity,
need infrequent watering and care, and are relatively easy to grow, Lithops make ideal houseplants. With their small size and slow, compact
growth these plants do not take up much room. Lithops
are long lived up to 40 or 50 years. It is quite possible to keep a plant
in the same pot for 10 or 20 years. Lithops are non-toxic to
humans or pets. (There are even some references to African children eating these
plants as a means to quench their thirst.) Their health in cultivation depends
on sufficient bright light, good soil drainage and proper watering.
Lithops can be grown successfully on a sunny windowsill (although a
greenhouse is preferred) where they receive about 4 or 5 hours of direct
sunlight during the early part of the day, and partial shade during the
afternoon. Usually a southern window is the best location; an unobstructed
eastern exposure is a good alternative.
If a plant does not receive enough sunlight it will begin to
grow slender and elongated, lean to one side to receive more light, lose
coloration and turn greenish, and will eventually die if better conditions are
not provided. But be cautious about moving a plant abruptly to brighter light
it could get sunburned and be fatally injured.
Lithops require well-drained soil, much the same as
cactus. Add sharp sand, perlite, decomposed granite or other gritty material
that will help improve drainage to regular houseplant potting mix, or use
special cactus potting mix. These plants have an extensive root system, which
means they need a larger pot than the plant size would indicate. Pots that are
about 3 to 5 inches deep with drain holes are recommended to allow the roots
adequate room to grow. Place the
top of the plant just slightly above the surface of the soil, rather than at the soil surface
as would occur in nature. Many growers topdress with gravel or surround the plant with stones
to give a more natural appearance.
Lithops have a yearly cycle of growth, and it
is essential to water only during certain stages and to keep the soil dry at
other stages of their growth. Over-watering is the chief cause of early demise.
Too much water and they rot or produce new bodies at the wrong time of year. Too
little water and they become stunted. How often you water depends on how quickly
the potting medium dries out. In general, drench the plant and leave it to dry
out completely (probably 1-2 weeks). Then wait a couple more days before
watering again. If in doubt....don't! It is best to
water in the mornings so that the excess water evaporates and the upper layers
of soil dry out fairly quickly. Some general guidelines for watering (but this
may vary somewhat by species):
-
Water from late spring into summer.
-
When the plant goes dormant in the summer, stop
watering. If the plant really shrivels, give just enough water to restore the
firm appearance of the plant, but only water until about the top one-half inch
of the soil is moistened.
-
Resume watering in late summer-early fall, when the
plants resume growth and bloom. The first sign of growth is when the fissure
between the leaves begins to separate in preparation for flowering.
- Lithops should be left totally dry throughout winter and spring.
Stop watering to allow the old leaf pair to dry out and the new pair develop. By early spring the new body should be visible. Watering can be resumed once the
remains of the old body are completely shriveled and dry. If water is given too
soon, the old "leaves" will try to continue to grow and the plant will not
develop properly. Remember, the old leaves should totally dry up as the new
leaves are growing.
Fertilize Lithops sparingly and use a low nitrogen, high potassium type.
Lithops can tolerate very high
temperatures as long as there is plenty of fresh air. Never allow the
plants to freeze.
Seed and plants of all species and many cultivars are today available from
specialist succulent nurseries. They grow quickly
from seed, and can be expected to flower in 3 to 4 years under optimal
conditions. Sow the seeds during the summer in sandy medium, covering
with a very thin layer of fine sand. Water the tiny seeds gently so you don't
displace them. Place the container in a warm sunny spot, keeping them moist but
not soggy. The first seeds should germinate in a few weeks (but germination may
be spread out over a long period of time, with stragglers taking as long as a
year). Once the seedlings are developing rapidly, reduce watering so that the
top Ό" of medium dries out, but the lower medium stays moist. Don't water too
much, as excessive
watering during this period may cause damping off of the seedlings. When the
plants
are 2-3 months old, start letting them dry out completely for a few
days between waterings, and gradually increase the length of the drying time.
The young plants can be transplanted when they are about a year old.
Lithops can also be propagated by dividing a multi-headed plant.
Lift the plant, carefully cut through the roots and replant them immediately.
Susan Mahr, University of Wisconsin
Additional Information:
Suggested Reference Books:
-
Flowering stones by D. T. Cole. 1988. Acorn Books, Randburg
-
Treasures of the Veld by S. Hammer and C. Barnhill. 1999.
British Cactus and Succulent Society
-
Growing the Mesembs by E. Storms. 1976. Fort Worth,
Texas.
- Mesembs of the World by Smith, et al. 1998. Briza, Pretoria
Some Mail-order Sources of Lithops:
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