Lithops - Au Cactus Francophone

lau”. > blau.
He goes on to say that L. summitata is “hellgrau blau am Kegelteil” and L.
karasmontana “taubengrau blau.” This assumes that there is a definite colour
called taubengrau blau. It is clear that these fine differences in colour cannot
possibly be used to distinguish species. Dr. Geyer, who had collected L. kara‑
smontana and the so called L. summitata, was asked by me to divide his fresh
material into as many groups as he could, based on the difference in colour of
the top surface. He found seven groups all more or less connected with one
another (Fig. 11). If one mixed them and were asked to pick the members
of the various groups, a different grouping would result in which the groups
would not contain the same plants as before. Dinter asserts that the weight of
the seed of L. summitata is 0.072 mg. and that of L. karasmontana is 0.064 mg.
That is driving the art of distinguishing species to a very fine point indeed.
To my mind there is only one species L. karasmontana, and I have come to
this conclusion after examining plants from each of two localities in which
L. karasmontana and L. summitata were found.
24
KEY FOR DETERMINING THE SPECIES
Only a few words are necessary concerning the key submitted here. As
has already been stated the flower is of no help in the delimitation of spe
cies in the genus. One is therefore reluctantly compelled to use the nature
and colour of the upper surface of the leaves for purposes of classification,
although it is realised that the key based on one organ and that the leaf
can never be entirely satisfactory.
The genus can conveniently be divided into two sections; (I) Afenestra‑
tae and (II) Fenestratae.
The first group consists of all those species in which the upper surface
appears to be opaque though in reality it lets enough light through for the
plants to thrive. The species of this group, with the exception of L. Meyeri, L.
turbiniformis, L. divergens, L. verruculosa and L. Van Zylii, are all found north
of the Orange River and are inhabitants of South West Africa. With the
exception of L. divergens they all grow in the neighbourhood of the Orange
Riser itself.
The second group Fenestratae includes those species in which the upper
surface is either entirely transparent or is perforated by transparent pellucid
area. The key will unfortunately not enable one to determine satisfactorily
certain species and in that case use should be made of the photographs and
coloured plates. In the case of some species the differences are quite obvious,
if the plants are placed alongside one another, but it is very difficult if not
impossible to describe these differences in words.
Ernst Rusch, an enthusiastic collector of succulents in South West Af
rica, found on examining seedlings of Lithops, that he could divide them into
two distinct groups, viz.; (A) the fissure is localised in the form of a small
aperture in the centre of the two leaves, and (B) the fissure separates the