The morphology of Lithops
A Lithops, an individual plant body, corpusculum or head, consists essentially of two opposite leaves which through the processes of evolution, have become thickened, fused together along the outer edges, and foreshortened, so as to form an obconic, turbiniform (top-shaped) body. This is like an inverted cone, tapering down to the point of junction with the root, and with a fissure across the top, dividing it into two more or less equal halves or lobes. In most species the lobes are fused together along their outer edges to a depth of 1-4 mm, according to the size of the plant, but there is a very thin line of adhesion closing the fissure across the top. Below this the cleft extends downwards, between the closely adpressed inner surfaces of the lobes, to the meristem or growing point immediately above the junction of the plant body with the root. When the plant flowers, the bud breaks through the line of adhesion in the middle of the fissure, thus opening up the cleft. Sometimes, perhaps more frequently in L. vallis-mariae than in other species, the cleft opens up even without flowering, resulting in a centrally widened fissure shaped like a narrow ellipse with pointed ends, and a gaping cleft.
Each year a new body, or sometimes two, and usually also a single flower develop from the meristem. As the flower bud develops it rises on its pedicel within the cleft until it breaks through the middle of the line of adhesion which seals off the cleft at the top; it then continues until the pedicel has reached its full extent, and in due course the flower opens just above the top surface or face of the plant.
During the so-called 'resting period' or 'dormant period' after flowering (for most species, the dry season, i.e. winter and early summer), the old body or head gradually shrivels and dries up, while the growth of the new body is accelerated by drawing nutriment from the old one which usually ends up as nothing more than a paper-thin shell tightly enveloping the new growth(s). The 'dormant period' is actually one of rapid growth and development for the new pair of leaves, though the old ones which envelop them are indeed in a state of dormancy and decline. After the first rain or watering, the new body absorbs water, swells out and bursts through the old shell, and the growth cycle commences again. The line of the fissure on the new body (or bodies) is roughly at right angles to that on the old growth(s); if two new heads are produced, the division between them is more or less in the same line as the fissure on the old body.
Size of plants
When one talks about the size of a Lithops, we are either talking about their facial diameters, or their size in terms of how many heads they possess. A plant which has one head is monocephalous, and one with multiple heads is polycephalous. Some species never develop more than one head, and others develop many heads with age. Facial diameters vary from species to species, and can be very small, to quite large.
Lithops flowers are mainly white, yellow or yellow with white centres, except for those of Lithops verruculosa which has various flower colours from white to yellow and sometimes even red/pink. The flowers open in the afternoon, and close just after the sun sets. On days where there is not much sun they do not open at all.
Facial features of plants
There are numerous terms used to describe the facial features of a Lithops, below is a list of some of the more widely used ones:
The Seed Capsules
The seed capsule of a Lithops is made up of a number of segments or loculi. The number of loculi that each seed capsule has differs from species to species, and even within the same species. There are usually five to six loculi, but there can be as many as 12. When it has fully matured the dried seed capsule will open up within a minute or two after being soaked by rain. This is due to the different expansion rates of the hydrated cells when wet. The force exerted by the raindrops that fall into the open capsule ejects the seeds. They can be ejected as far as 30 cm away from the plant. When the rain stops the capsule dehydrates and it closes once more protecting any remaining seeds .
* Information from COLE, DESMOND T. and NAUREEN A., (2005) Lithops Flowering Stones, Cactus&Co. Libri
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