Commonly known as 'living stones', the genus of plants called Lithops is one of the most popular among collectors of cacti and succulents. As they learn more about their new pastime, it's common for growers take a shine to one or two particular types of cactus or succulent, specialising in these plants and making them the focus of their collection. Lithops is one of the most frequently chosen genera in this respect.

They're called living stones because in their natural habitat they have evolved to mimic the stones and pebbles which often litter the ground where they grow. As stones can be different colours, so are Lithops. The hues and patterns produced by these plants is astonishing. The reason they have developed this ability to look like stones is really very obvious. There are many small mammals which share the same arid habitat as Lithops - animals which would be only too glad to bite into the juicy leaf of a succulent and quench their thirst on the abundant liquid therein. The thick skin of the top of a Lithops leaf is also a deterrent to most insects.

Of course, no defence is 100% effective, and there are insects and mammals which prey on Lithops, particularly the Bush Cricket (Acanthoplus discoidalis), the Cape Porcupine (Hystrix africaeaustralis), and the Cape Ground Squirrel (Xerus inaurus).

Although commonly called living stones, Lithops have been known by other names. Local Afrikaaners called them beeskloutjies - or 'cattle hoof,' and skaappootjies - 'sheep hoof,' and they have also been called 'belly plants', presumably because you have to crawl on your belly in order to find them! In Namibia they are sometimes known as ombuma yombwa or dog testicles.

Distribution and history

Lithops are native to southern Africa, and have been found growing wild in only three countries - Namibia, Botswana, and South Africa. They are found almost exclusively in habitats classed as desert. To be a true desert, an area must receive on average less than 10" (25.4cm) of rain a year. Most Lithops live in places lucky to see a fifth of that amount. These plants live on the edge of survival.

It was the botanist William John Burchell who, on a trip to the northern Cape Province of South Africa in 1811, bent down to look at an odd-looking stone and found it to be not a stone at all but a plant. He named it Mesembryanthemum turbiniforme. However, the official naming of the plant is credited to another botanist - Adrian H Howarth, who used Burchell's original drawing to publish a description of it in 1821 - one year before Burchell did the same in his book Travels in the Interior of Southern Africa. A century later the plant was reclassified as Lithops turbiniformis when the genus of plants previously called Mese/mesembryanthemum was split into more than 100 separate genera, forming the Mesembryanthemaceae family. The name Lithops was coined in 1922 by botanist Dr Nicholas E Brown, who combined two Greek words - lithos meaning 'stone' and ops meaning 'face'. Lithops turbiniformis has since been reclassified a second time, and is now more usually referred to as Lithops hookeri var. turbiniformis.

In recent years there has been some debate as to whether the Mesembryanthemaceae should be included in the Aizoaceae¹ family. This has yet to be conclusively resolved. For the botanists amongst you, the official classification of the genus Lithops is as follows:

• Kingdom: Plantae
• Phylum: Angiospermae
• Class: Dicotyledonae
• Order: Caryophyllidae
• Suborder: Caryophylles
• Family: Mesembryanthemaceae (or Aizoaceae)
• Subfamily: Ruschioidene Schwant
• Subtribe: Lithopinae Schwant
• Genus: Lithops

Natural habitat

Lithops can be found growing in many different types of soil - limestone, sandstone, granite, or shale - but they have one thing in common: they are all very free-draining. Mostly they grow in areas of desert scrub where plantlife is scarce, but they can also be found growing among grass. Some grow at sea-level and others at altitudes as high as 7,500 ft (2,280m). They can survive temperatures of 115° Fahrenheit (46° Celsius), but will frequently be subjected to night-time lows that are barely above freezing. Some species have extensive root systems, tapping water resources deep within the soil, while others have almost no roots and get most of their moisture from mist and early morning dew.

What do they look like?

The basic Lithops shape when viewed from the top - and that's normally all you can see of them - is an oval, usually no bigger than an inch (25mm) across, divided by a fissure across the middle. The two halves of this oval are the leaves, which have adapted to the dry conditions of the plant's habitat by turning into thick, juicy water-storage facilities. When removed from the ground and viewed side-on, Lithops are the shape of an upturned cone, the 'base' of the cone being the flat top of the leaves, and the point being the place where they emerge from the roots. This leaf pair is called a 'head'.

It is the colours and patterns decorating that flat top which delight the eyes and make these plants so sought-after by collectors. They vary not just from species to species, but even within species. From the reds and browns of Lithops lesliei, Lithops aucampiae, and Lithops hookeri, to the greys and greens of Lithops olivacea, Lithops marmorata, and Lithops salicola. Like snowflakes, no two Lithops are ever the same.

Growing cycle

Lithops appear dormant for much of the year, but at the beginning of their growing season the head will put out a white or yellow daisy-like flower which lasts for three to five days. After the flower has died it may seem like nothing is happening for a while, but, like a swan on a lake, whilst everything seems calm and serene on the surface it's all going like the clappers underneath.

Deep in the plant a new leaf-pair is forming. Over the next two or three months this new pair grows bigger, and eventually the fissure on top of the plant will begin to split apart, revealing the new head within, and growing at roughly 90° to the old head. The fissure becomes wider still, and the new head gradually emerges, pushing the old leaves apart and then down. This all happens during the southern hemisphere summer when rainfall is lowest, and the new head derives all its moisture from the old leaves, which gradually shrivel and become a dry, parchment-like collar around the base of the plant.

Every so often, the plant will produce four leaves instead of two - two heads instead of one. The following year, each head will revert to normal, producing one flower and two new leaves, but after a number of growing seasons one or both of the heads will again double up. Over many years, one head can form a clump a foot or more across and containing 20 or 30 heads - a spectacular sight when in bloom. The propensity to produce multiple heads depends largely upon the species - some never grow more than three or four, others a couple of dozen. A handful of particularly long-lived Lithops have been recorded as having over 200 heads.

On rare occasions², a Lithops head will produce three leaves instead of two. This abnormality is not usually reproduced in successive years, and the plant will revert to the normal, even number of leaves the following season.

Growing Lithops at home

Not the easiest of plants to grow, Lithops can however be persuaded to flourish with a few simple rules and a degree of care. A greenhouse, while not absolutely necessary, is an advantage if you live in a temperate climate.

Soil

As already mentioned, Lithops prefer free-draining soil. Ready-made cactus soil can be bought at most nurseries and garden centres, and Lithops will grow well in it, but they will fare even better if you add one part of sharp sand to two parts of cactus soil. If you are unable to find specialist cactus soil, you can make your own Lithops mixture with one-part potting compost, one-part peat or coir-based compost (Lithops prefer a little acidity), one-part sharp sand or grit, and one-part small broken crock pieces or gravel.

Water

The most important rule is not to overwater these plants. In the wild they often survive for months on end without water, and they can do the same in captivity. During the summer they should be given a light watering about once a month, and the soil should always be allowed to dry out completely before the next watering - Lithops cannot stand moist soil and will soon rot if their roots remain wet for more than a few days. If you live in the northern hemisphere³, they will flower in mid to late autumn. As soon as flowering ceases, so should all watering. From this point on the new leaves forming within the plant are draining moisture from the existing leaves. No more water will be needed until the old leaves have almost completely dried up, although it is beneficial to mist them once a week with a fine spray of water. If watering continues, one (or possibly both) of two things will happen: either the plant will rot and die, or the old leaves will fail to wither.

In the wild, Lithops are almost entirely embedded in the soil, only showing their top surface. In cultivation they usually stand proud of the soil because the collector is giving them more than ideal growing conditions and a more regular water supply than they will usually get in their natural habitat. Indeed, it's not unknown for a Lithops head to split open because it has been given too much water. Using a terracotta or unglazed clay pot instead of a plastic one will help the soil to dry out more quickly by allowing water to evaporate through its sides.

Heat and light

Too much sunlight can burn a Lithops - or rather, cook it from the inside out, as the water held in its tissues heats up. In their natural habitat they are usually shaded for part of the day by rocks, shrubs, or other plants larger than themselves. If you are cultivating Lithops in tropical and sub-tropical climates, they will benefit from some direct sunlight, but not all day long, especially in a greenhouse. In higher latitudes this isn't quite as important; in fact they may need day-long direct sun in order to receive enough light - too little light can cause them to become tall and straggly as they search for as much sunshine as they can get, and their colours will be relatively pale and washed out.

They will grow best if the daytime temperature is kept between 75° and 95°F (24° to 35°C) during the summer, and not allowed to fall below 50°F (10°C) during the winter. They can be kept at cooler temperatures but will not withstand a frost, prefer a dry, arid atmosphere, and will not do as well in high humidity.

Feeding

In the wild, Lithops exist on the margins of survival and have evolved to grow where nutrients are few and far between. Feeding them in cultivation is not necessary - too much in the way of fertiliser can make them grow too quickly and become unnaturally large.

Still interested?

Any specialist cactus and succulent nursery worth its salt will sell a selection of Lithops - they'd be daft not to stock such a popular plant. A quick web search should reveal your nearest nursery. The Cactus Mall is one of, if not the, best Internet resources for all things cactus and succulent. It has lists not only of suppliers, but also of cactus and succulent societies around the world.

Don't be too disappointed if one or more of your Lithops die off in the first two or three seasons - they really are quite difficult to grow. Just remember the rules about watering. If you've never grown cacti or succulents before, there are plenty of hints here.