Lithops is a genus of succulent plants in the ice plant family, Aizoaceae. Members of the genus are native to southern Africa. They avoid being eaten by herbivores with their camouflage as small stones, and are often known as pebble plants or living stones.
"Lithops" is both the genus name and the common name, and is singular as well as plural. The name is derived from the Ancient Greek words λίθος (líthos) 'stone' and ὄψ (óps) 'face', referring to the stone-like appearance of the plants.
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 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.[2]
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. Yellow or white flowers emerge from the fissure between the leaves after the new leaf pair fully matures, 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.
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 700mm/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 and care for if given sufficient sun and kept in well-draining soil.
Normal treatment in mild temperateclimates is to keep them completely dry during winter, watering only when the old leaves have dried up and are replaced by a new leaf pair. Watering continues through autumn, when the plants flower, and then stops for winter. The best results are obtained in an environment 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 most species will flower at approximately the same time.
Lithops olivacea
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.[3]
Since Lithops are mostly propagated by seed, cultivars require to be stabilised as seed strains. Most cultivars are either abnormally green or abnormally red plants, lacking most of the normal leaf pigments. Some were initially found as isolated unusual plants in habitat, but increasingly have arisen from cultivation, sometimes by deliberately selecting mildly-coloured plants to achieve intense colours for a cultivar. The term "aberrant colour form" (acf.) has been used for these unusually-coloured Lithops.[11]
There are also so-called "pattern cultivars" of Lithops, seed strains which have been selectively-bred or stabilised from isolated unusual plants to have intensified or unusual leaf patterns, and sometimes unusual flowers. In some cases, these are hybrids.[10]
Propagation
Lithops seedlings
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.
Conservation status
At least half of the species listed in the Red List of South African Plants are classified as endangered or threatened for various reasons, including poaching for the succulent horticultural trade, habitat degradation, and decreased or restricted range due to urban and agriculture expansion.[12]
The first scientific description of Lithops was made by botanist and artist William John Burchell, explorer of South Africa, although he called it Mesembryanthemum turbiniforme. In 1811, Burchell discovered a specimen when picking up a "curiously shaped pebble" from the ground.[11] Unfortunately the documented physical description was 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 Mesembryanthemumspecies until in 1922 N E Brown started to split up the overly large genus on the basis of the capsules. The genusLithops 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 remained rather unknown in cultivation and was not well understood taxonomically.
In the 1950s, Desmond and Naureen Cole began to study Lithops. Together, the couple visited nearly all natural habitats of the different lithops populations and collected samples from approximately 400. They document and identify them, assigning a number, which is now known as the Cole number still used today all 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. Recent discoveries include L. coleorum in 1994, L. hermetica in 2000, and L. amicorum in 2006.[13]
Taxonomy
Lithops fulviceps 'Aurea', green-bodied cultivar
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. The species list here follows Cole & Cole (2006).[11]
Although the species, subspecies, and varieties published by Cole & Cole[11] largely remain accepted and in widespread use,[14] some variations have been published by other authors. Some published changes since 2006 include:
reducing L. amicorum to a subspecies of L. karasmontana; combining L. karasmontana ssp. bella and ssp. eberlanzii into one subspecies; and combining L. herrei with L. optica.[16]
raising L. dendritica and L. eberlanzii to species level and dropping all the separate varieties of L. karasmontana.[17]
raising L. bella, L. burchellii, L. euniceae, and L. glaudinae to species level; combining L. dorotheae and L schwantesii var. marthae under L. dinteri; combining L. francisci, L. gesinae, and L. hermetica; combining L. geyeri under L. herrei; dropping separate subspecies of L. julii and L. gracilidelineata; splitting ssp. archerae, dendritica and groendrayensis from L. pseudotruncatella as L. dendritica; and dropping separate varieties under L. villetii.[18]
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
Related Research Articles
The Aizoaceae, or fig-marigold family, is a large family of dicotyledonous flowering plants containing 135 genera and about 1800 species. Several genera are commonly known as 'ice plants' or 'carpet weeds'. The Aizoaceae are also referred to as vygies in South Africa and New Zealand. Some of the unusual Southern African genera—such as Conophytum, Lithops, Titanopsis and Pleiospilos —resemble gemstones, rocks or pebbles, and are sometimes referred to as 'living stones' or 'mesembs'.
Sempervivum is a genus of about 40 species of flowering plants in the family Crassulaceae, commonly known as houseleeks. Other common names include liveforever and hen and chicks, a name shared with plants of other genera as well. They are succulent perennials forming mats composed of tufted leaves in rosettes. In favourable conditions they spread rapidly via offsets, and several species are valued in cultivation as groundcover for dry, sunny locations.
Coleus scutellarioides, commonly known as coleus, is a species of flowering plant in the family Lamiaceae, native to southeast Asia through to Australia. Typically growing to 60–75 cm (24–30 in) tall and wide, it is a bushy, woody-based evergreen perennial, widely grown for the highly decorative variegated leaves found in cultivated varieties. Another common name is painted nettle, reflecting its relationship to deadnettles, which are in the same family. The synonyms Coleus blumei, Plectranthus scutellarioides and Solenostemon scutellarioides are also widely used for this species.
The Desert Garden Conservatory is a large botanical greenhouse and part of the Huntington Library, Art Collections and Botanical Gardens, in San Marino, California. It was constructed in 1985. The Desert Garden Conservatory is adjacent to the 10-acre (40,000 m2) Huntington Desert Garden itself. The garden houses one of the most important collections of cacti and other succulent plants in the world, including a large number of rare and endangered species. The 3,000-square-foot (280 m2) Desert Garden Conservatory serves The Huntington and public communities as a conservation facility, research resource and genetic diversity preserve. John N. Trager is the Desert Collection curator.
Lithops aucampiae is a species of flowering plant in the family Aizoaceae, found in South Africa. it was named after Juanita Aucamp, who found a specimen on her father's farm in Postmasburg, Northern Cape in 1929.
Lithops viridis is a species of plant in the family Aizoaceae.
Lithops salicola is a species of perennial plant in the family Aizoaceae, often called living stones, because of its resemblance to round grey pebbles.
Lithops francisci, commonly known as one of the living stones or pebble plants, is in the family Aizoaceae. It is endemic to the arid desert environments of Namibia. It is a succulent with a natural habitat in rocky areas. L. francisci was assessed by Nicholas Edward Brown in 1925. It is one of the Lithops plants and shares the characteristic bi-leaf head pattern separated by a deep fissure, the bottom of which houses and protects the stunted stem.
Lithops karasmontana, is a species of flowering plant in the ice plant family Aizoaceae, native to Namibia and South Africa.
Lithops lesliei is a species of plant in the family Aizoaceae. The plant is collected for its medicinal properties, and has therefore become threatened.
Lapidaria is a monotypic genus of dwarf succulent plants in the family Aizoaceae. The only species it contains is Lapidaria margaretae, also known as the Karoo rose.
Lithops amicorum is a small succulent plant with white flowers, one of the smallest in the genus. It was named for the group of four friends who discovered it. It was collected by Desmond T. and Naureen A. Cole on 3 May 2004. After recent molecular analysis it was recombined to be a subspecies of Lithops karasmontana rather than its own species.
Lithops coleorum is a small flowering succulent plant of the family Aizoaceae. It is native to the Northern Provinces of South Africa.
Lithops olivacea is a species of the genus Lithops under the family Aizoaceae. The name olivacea refers to the Latin word for olive (oliva) combined with the suffix -cea, meaning "of the likeness", producing the idea of "olive likeness". Lithops olivacea grow primarily in the Bushmanland of South Africa. They grow most abundantly in the regions of Aggeneys, Pofadder, and Namies. L. olivacea also received the Royal Horticultural Society's Award of Garden Merit for being "excellent for ordinary use in appropriate conditions, available to buy, of good constitution, essentially stable in form & colour, [and] reasonably resistant to pests & diseases."
Lithops schwantesii is a succulent plant of the genus Lithops and a member of the family Aizoaceae. L. schwantesii receives its name from Gustav Schwantes, a prominent archaeologist and botanist of late 19th and 20th century. The succulent also received the Royal Horticultural Society's Award of Garden Merit for being a resilient and easy to cultivate plant.
Lithops pseudotruncatella is a species of succulent in the family Aizoaceae. Initial confusion associated with Conophytum truncatum is where it derives its name, literally meaning "fake-truncatum". It also received The Royal Horticultural Society's Award of Garden Merit. The plant is endemic to Namibia.
Lithops divergens is a succulent plant species in the genus Lithops of the family Aizoaceae. It is endemic to the western Cape Provinces of South Africa. It is able to withstand intense climatic changes due to its resilience as a succulent. The average annual rainfall for its natural environment is less than 150 mm, occurring primarily in winter which is unusual for a Lithops.
Lithops villetii is a species of the genus Lithops under the family Aizoaceae. The succulent plant is named after C. T. Villet. It is native to the Calvinia District, Namaqualand, Northern Cape, South Africa.
Lithops otzeniana is a species of succulent plant under the genus Lithops. It belongs to the family Aizoaceae. L. otzeniana is native to the Northern Cape province of South Africa. It derives its name from M. Otzen, who invited its discoverer, G.C. Nel, on the trip in which he discovered it.
Lithops naureeniae is a species of pebble plant (Lithops), in the family Aizoaceae. It is native to the Northern Cape province of South Africa. The succulent is adapted to the desert climate in which it lives. L. naureeniae was identified in 1980 by Desmond Cole, who became involved in Lithops research in 1947, from a specimen provided to him by Bruce Bayer, curator of the Karoo Botanic Garden, having been collected by Peter V. Bruyns in Namaqualand. It is named after Cole's wife, Naureen Cole. Cole wrote:
I therefore have pleasure in dedicating it to the person who, during the last fifteen years, directly and indirectly, has contributed more to research on and knowledge of the genus Lithops than any other—my wife, Naureen
References
↑ "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.
↑ Earlé, Roy A.; Young, Andrew J. (2020). "The form, structure and size of Lithops N.E.Br. Seeds and the taxonomic implications". Bradleya. 2020 (38): 195. doi:10.25223/brad.n38.2020.a20. S2CID220072147.
↑ H Jainta (2019). "Ein neuer taxonomischer Ansatz für die Gattung Lithops N.E.Br". Avonia. 37 (1).
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