Lithops

Lithops is a genus of succulent plants in the ice plant family, Aizoaceae. Members of the genus are native to southern Africa. The name is derived from the Ancient Greek words λίθος (lithos), meaning "stone," and ὄψ (ops), meaning "face," referring to the stone-like appearance of the plants. They avoid being eaten by blending in with surrounding rocks and are often known as pebble plants or living stones. The formation of the name from the Greek "-ops" means that even a single plant is called a Lithops.

"Living stone" redirects here. For the 1958 documentary film, see The Living Stone.

Lithops
Lithops sp. by Marloth
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Caryophyllales
Family: Aizoaceae
Subfamily: Ruschioideae
Tribe: Ruschieae
Genus: Lithops
N.E.Br.[1]
Species

See text

Description
Lithops hookeri. Two new leaf pairs are emerging between the old one, leading to a double-headed plant

Individual Lithops plants consist of one or more pairs of bulbous, almost fused leaves opposite to each other and hardly any stem. The slit between the leaves contains the meristem and produces flowers and new leaves. The leaves of Lithops are mostly buried below the surface of the soil, with a partially or completely translucent top surface known as a leaf window which allows light to enter the interior of the leaves for photosynthesis.

During winter a new leaf pair, or occasionally more than one, grows inside the existing fused leaf pair. In spring the old leaf pair parts to reveal the new leaves and the old leaves will then dry up. Lithops leaves may shrink and disappear below ground level during drought. Lithops in habitat almost never have more than one leaf pair per head, presumably as an adaptation to the arid environment. Yellow or white flowers emerge from the fissure between the leaves after the new leaf pair has fully matured, one per leaf pair. This is usually in autumn, but can be before the summer solstice in L. pseudotruncatella and after the winter solstice in L. optica. The flowers are often sweetly scented.

Longitudinal section of a Lithops plant, showing the epidermal window at the top, the translucent succulent tissue, the green photosynthetic tissue, and the decussate budding leaves growing between the mature leaves.

The most startling adaptation of Lithops is the colouring of the leaves. The leaves are fenestrated, and the epidermal windows are patterned in various shades of cream, grey, and brown, with darker windowed areas, dots, and red lines, according to species and local conditions. The markings function as remarkable camouflage for the plant in its typical stone-like environment. As is typical of a window plant, the green tissue lines the inside of the leaves and is covered with translucent tissue beneath the epidermal windows.

Lithops are obligate outcrossers and require pollination from a separate plant. Like most mesembs, Lithops fruit is a dry capsule that opens when it becomes wet; some seeds may be ejected by falling raindrops, and the capsule re-closes when it dries out. Capsules may also sometimes detach and be distributed intact, or may disintegrate after several years.

Distribution
Large stand of Lithops salicola

Lithops occur naturally across wide areas of Namibia and South Africa, as well as small bordering areas in Botswana and possibly Angola, from sea level to high mountains. Nearly a thousand individual populations are documented, each covering just a small area of dry grassland, veld, or bare rocky ground. Different Lithops species are preferentially found in particular environments, usually restricted to a particular type of rock. Lithops have not naturalised outside this region.

Rainfall in Lithops habitats ranges from approximately 700 mm/year to near zero. Rainfall patterns range from exclusively summer rain to exclusively winter rain, with a few species relying almost entirely on dew formation for moisture. Temperatures are usually hot in summer and cool to cold in winter, but one species is found right at the coast with very moderate temperatures year round.

Cultivation
Group of Lithops sp. dividing and producing new leaf growth.

Lithops are popular house plants and many specialist succulent growers maintain collections. Seeds and plants are widely available in shops and over the Internet. They are relatively easy to grow if given sufficient sun and a suitable well-drained soil.

Normal treatment in mild temperate climates is to keep them completely dry during winter, watering only when the old leaves have dried up and been replaced by a new leaf pair. Watering continues through autumn when the plants flower and then stopped for winter. The best results are obtained with additional heat such as a greenhouse. In hotter climates Lithops will have a summer dormancy when they should be kept mostly dry, and they may require some water in winter. In tropical climates, Lithops can be grown primarily in winter with a long summer dormancy. In all conditions, Lithops will be most active and need most water during autumn and each species will flower at approximately the same time.

Lithops thrive best in a coarse, well-drained substrate. Any soil that retains too much water will cause the plants to burst their skins as they over-expand. Plants grown in strong light will develop hard strongly coloured skins which are resistant to damage and rot, although persistent overwatering will still be fatal. Excessive heat will kill potted plants as they cannot cool themselves by transpiration and rely on staying buried in cool soil below the surface. Commercial growers mix a mild fungicide or weak strength horticultural sulfur into the plant's water to prevent rotting. Lithops are sensitive to watering during hot weather, which can cause the plants to rot; in habitat the plants are often dormant when the temperatures are high, doing most of their growing during the cool months of the year. Low light levels will make the plants highly susceptible to rotting and fungal infection.[2]

Lithops olivacea

In the United Kingdom the following species have gained the Royal Horticultural Society’s Award of Garden Merit:-[3]

Propagation

Propagation of Lithops is by seed or cuttings. Cuttings can only be used to produce new plants after a plant has naturally divided to form multiple heads, so most propagation is by seed. Lithops can readily be pollinated by hand if two separate clones of a species flower at the same time, and seed will be ripe about 9 months later. Seed is easy to germinate, but the seedlings are small and vulnerable for the first year or two, and will not flower until at least two or three years old.

History

The first scientific description of a Lithops was made by botanist and artist William John Burchell, explorer of South Africa, although he called it Mesembryanthemum turbiniforme. In 1811 he accidentally found a specimen when picking up from the ground a "curiously shaped pebble".[9] Unfortunately his description is not detailed enough to be sure which Lithops he had discovered and the name Lithops turbiniformis is no longer used, although for many years it was applied to what is now known as Lithops hookeri.

Several more Lithops were published as Mesembryanthemum species until in 1922 N E Brown started to split up the overly large genus on the basis of the capsules. The genus Lithops was created and dozens more species were published in the following decades. Brown, Gustav Schwantes, Kurt Dinter, Gert Nel, and Louisa Bolus continued to document Lithops from across southern Africa, but there was little consensus on the relationships between them, or even which populations should be grouped as species. As recently as the 1950s, the genus was little known in cultivation and not well understood taxonomically.

In the 1950s, Desmond and Naureen Cole began to study Lithops. They eventually visited nearly all habitat populations and collected samples from approximately 400, identifying them with the Cole numbers which have been used ever since and distributing Cole numbered seed around the world. They studied and revised the genus, in 1988 publishing a definitive book (Lithops: Flowering Stones) describing the species, subspecies, and varieties which have been accepted ever since.

Because their camouflage is so effective, new species continue to be discovered, sometimes in remote regions of Namibia and South Africa, and sometimes in well-populated areas where they simply had been overlooked for generations. Recent discoveries include L. coleorum in 1994, L. hermetica in 2000, and L. amicorum in 2006.

Taxonomy

Many of the species listed have named subspecies or varieties and some have many regional forms identified by old names or habitat locations. Identification of species is primarily by flower colour and leaf patterns.

Lithops[10]
Specific epithet Meaning
amicorum[11] of the friends
aucampiae named after Juanita Aucamp
bromfieldii named after H. Bromfield
coleorum named after Desmond & Naureen Cole
comptonii named after Prof. Robert Harold Compton
dinteri named after Moritz Kurt Dinter
divergens divergent lobes
dorotheae named after Dorothea Huyssteen
francisci named after Frantz de Laet
fulviceps (a.k.a. lydiae) tawny head
gesineae named after Gesine de Boer
geyeri named after Dr. Albertus Geyer
gracilidelineata thin lined
hallii (a.k.a. salicola var. reticulata) named after Harry Hall
helmutii named after Helmut Meyer
hermetica named after the location 'hermetically sealed', Sperrgebiet
herrei named after Adolar 'Hans' Herre
hookeri (a.k.a. dabneri, marginata, turbiniformis var. lutea) named after Sir Joseph Hooker
julii (a.k.a. fulleri) named after Dr. Julius Derenberg
karasmontana named after the Great Karas Mountains
lesliei named after T. N. Leslie
localis (a.k.a. terricolor, peersii) of a place
marmorata (a.k.a. diutina, framesii, umdausensis) marbled
meyeri named after Rev. Gottlieb Meyer
naureeniae named after Naureen Cole
olivacea olive-green
optica (a.k.a. rubra) eye-like
otzeniana named after M. Otzen
pseudotruncatella had been confused with Conophytum truncatum (a.k.a. Mesembryanthemum truncatellum)
ruschiorum named after Rusch family
salicola salt-dweller
schwantesii named after Gustav Schwantes
vallis-mariae named after the location Mariental (Latinised)
verruculosa warty
villetii (a.k.a. deboeri) named after Dr. C. T. Villet
viridis green
werneri named after Werner Triebner
  • Lithops sp. Blooms emerge between the leaves in autumn.
  • Lithops sp. Some species have flowers large enough to obscure the leaves. They open in the afternoon and close in the evening.
  • Sculpture of lithops, National Botanical Gardens of Ireland
gollark: I could probably add a "force no _G setting" mode to potatOS, but everything would break.
gollark: There was that one time I built a well-hidden rootkit which would randomly edit local variables using debug in programs.
gollark: CC also has debug and bytecode, which are !!FUN!!.
gollark: I mostly work around that by making my programs store vast amounts of state on disk. Which they should do anyway in case of e.g. power failure.
gollark: I should make PotatOS allocate a billion-element table on every computer on April Fools' day.

References
  1. "Genus: Lithops N. E. Br". Germplasm Resources Information Network. United States Department of Agriculture. 2009-06-09. Archived from the original on 2012-10-11. Retrieved 2011-04-09.
  2. Ed Storms (1986). The New Growing the Mesembs. Storms.
  3. "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 61. Retrieved 25 March 2018.
  4. "RHS Plantfinder - Lithops karasmontana". Retrieved 25 March 2018.
  5. "RHS Plantfinder - Lithops olivacea". Retrieved 25 March 2018.
  6. "RHS Plantfinder - Lithops pseudotruncatella". Retrieved 25 March 2018.
  7. "RHS Plantfinder - Lithops salicola". Retrieved 25 March 2018.
  8. "RHS Plantfinder - Lithops schwantesii". Retrieved 25 March 2018.
  9. Cole, Desmond; Cole, Naureen (2005). Lithops—Flowering Stones. Cactus & Co. ISBN 88-900511-7-5.
  10. Hartmann, H.E.K., ed. (2001). Illustrated Handbook of Succulent Plants: Aizoaceae F-Z. Springer. ISBN 3-540-41723-0.
  11. Cole, Desmond (2006). "Cactus&Co Journal". X(1). Cactus&Co: 57–59. Cite journal requires |journal= (help)

Literature
  • Jainta, Harald (2017). Wild Lithops. Klaus Hess Verlag. ISBN 978-3-933117-93-9.
  • Cole, Desmond T (1988). Lithops—Flowering Stones. Acorn Books. ISBN 0-620-09678-0.
  • Cole, Desmond; Cole, Naureen (2005). Lithops—Flowering Stones. Cactus & Co. ISBN 88-900511-7-5.
  • Hammer, Steven (1999). Lithops: Treasures of the Veld. BCCS. ISBN 0-902099-64-7.
  • Schwantes, Gustav (1957). Flowering Stones and Mid-day Flowers. London: Ernst Benn.
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