T C. Rochford
Distribution of Succulents
Although the only cacti growing in the wild which most of us see are round the shores of the Mediterranean, the species is exclusively American in its origins. Other succulents come from all five continents of the world and although the cactus family has established itself over nearly as wide a geographic area it is entirely a product of the New World. In prehistoric times, however, some species of cactus travelled and Rhipsatis cassutha, for example, has been growing in Africa for a considerable time. Pliny, too. knew about opuntias and this suggests that seeds must have crossed the Atlantic, possibly with birds on their migrations as both species have attractive berries. Within America itself the cactus family is most heavily concentrated in Mexico but there are also large numbers of species in Southern and Northern America.
In spite of this concentration of the cacti around the Equator the family is very tolerant in its requirements and representatives are found in sub-arctic regions in both north and south. Altitude too seems to make little difference and some species actually grow near the edge of the snow line. However, before pulling down your greenhouse and planting up your garden with these fascinating plants, I should point out that the air is very much less humid in these regions than in Britain and like many alpine plants cacti cannot cope with the cold damp weather that is so characteristic of a British
Generally the more distantly spaced members of the family tend to be rarer in cultivation. Pterocactus valeniinii is supposedly one of the most southern species as it is a native of Patagonia, and Opuniia polyacaniha grows at 56° North in Canada near the Peace river. Oreocereus Irollii can be found on mountain ranges to a height of some 13.000 ft (4.000 m) but opuntias, which are able to grow so far north, probably hold the record with Optuuia floccosa growing at a height of 17.000 ft (5.300 m) in some isolated cases. The most easterly species is Monvillea insular is.
Succulents other than cacti are far more generally distributed throughout the world occurring not in the true deserts such as the Gobi, the Sahara and the great central desert in Australia but in the semi-deserts. Succulents adopt their fleshy characteristics for reasons of water conservation and there are many species of coastal plant which can be considered as succulent, especially plants which are found in British tidal waters and whose succulence arises from the need to conserve fresh water within the plant as opposed to brine. The main families in which succulence occurs are the Crassulaceae, represented in Britain by sedums and sempervivums, the Euphorbiaceae represented in Britain by the largely non-succulent spurges, the Aizoaceue,
The main natural distribution areas of cacti and other succulents which is largely represented in British gardens by the mesembryanthemums, although the Kaffir fig is naturalized in certain parts. The Amaryllidaceae and the Liliaceae also somewhat surprisingly produce succulent varieties, and the other major family is Asclepiadaceae. although there are no wild succulent members of these last three groups in Britain. Many other families have some succulents among them : the Compositae or dandelion family has some rather unexpected relatives, and well known house plants such as pelargoniums and tradescantias can also exhibit succulent relatives.
With such a wide variation it is not surprising that it is difficult to generalize about the distribution of succulents other than cacti, but, and this is being very general indeed, the most significant areas for the Aizoaceae and Euphorbiaceae are Southern Africa while the Crassulaceae have a very much more general distribution, some succulent species being found in nearly every major country. The succulent Amaryllidaceae and Liliaceae can be divided in turn into the agaves, which are largely American and West Indian in origin, and the somewhat similar aloes, which are natives of Southern Africa, together with their relatives haworthia and gasteria.
The succulents have developed their strange forms in response to the challenge of their environment, and 94 although the areas in which they grow are not totally devoid of water during the year, there are long periods of drought during which the water accumulated during the short but intense wet period must be carefully stored and used to best advantage. The original forebears of the cacti were probably leafy shrubs similar in appearance to pereskia, and although relatives of the opuntias have been found in fossil forms in deposits going back some fifty million years it is possible that they achieved some separate identity at a still earlier stage.
At this point it would be as well to draw the distinction between cacti and other succulents which is fundamental to the understanding of the different cultural requirements of each group of plants, and which is equally important to finding your way around this part of the book as the cacti have been put on pages 100 to 164 and the other succulents have been put on the pages that follow. The illustration shows some typical features of succulents. The spines are in fact the equivalent to leaves on conventional plants and have achieved their present shape through the need to reduce transpiration (the evaporation of the water from the plant bodies). They are divided into two groups, centrals, which are generally the larger ones and occur at the centre of the cluster, and radials, which radiate round the sides of the cluster. The spines arise from a felted or hairy base or pad which may also support hairs or bristles and which in certain families produces the flowers. The felting or hair is peculiar to the cacti and is one of the most important distinguishing features of the group. If your spiny unknown plant has no hair.
look for it amongst the succulents in this book, if there is any hair present round the base of the spines at all, you must look for it amongst the cacti. Where this soft pad exists it is called the areole, and the presence of areoles distinguishes cacti from all other succulents. The stems have become globular, cylindrical or even flattened plant bodies and these may be characterized by the presence of tubercles or elongated points, or by ribs running up the sides of the plant. Some cacti, notably pereskias, have real leaves but still produce areoles on the stem between them. Opuntias, too, produce rudimentary leaves especially on the young growth although only a few species actually overwinter with their leaves. Many of the euphorbias, on the other hand, which have a superficial resemblance to cacti but lack the distinctive areoles, produce leaves which can persist for several seasons if given a moist humid
Some of the typical features of cacti. A close-up of an areole is shown on the left specimens in a solution of benomyl until the bubbles stop rising from the compost.
While fungal attacks are the most trying features of cactus collections, pests are more easily controlled and generally do less harm than they do to less tough house plants. Nearly all the standard household pests attack succulents. Ants, for example, can be a problem through their tunnelling in the soil, and also because they carry aphids around, a proprietary ant killer is the best cure. Mealy bug is by far the most common pest; malathion may be used to control it in most cases although care should be taken before spraying some crassulas and you should refer to the appropriate entry in this book, especially if their skin is greyish or felted at all. As an alternative to malathion a matchstick dipped in methylated spirits can be used for a spot kill. The treatment should be repeated at fourteen-day intervals until the infestation is clear. Red spider mite is normally found on cacti, euphorbias and mesembryanthemums. It is a difficult pest to kill and many chemicals which were effective a few years ago are no longer of any use as the mite is now resistant to them. A nicotine solution can be effective if sprayed on carefully, but it is probably best to use one of the systemic insecticides which act through the stem of the plant. Scale insects can be very troublesome pests. As their name implies they appear like small scales on the plant; the insect itself lives under this scale-like shell, which is generally impervious to chemicals, so routine spraying will be ineffective. If systemic insecticides do not solve the problem, then the insects will have to be removed with a pointed stick. Other common garden pests such as greenfly (aphids) are best killed with the normal proprietary insecticides.
Cacti are particularly susceptible to diseases, especially fungal attacks through lack of hygiene in the soil or the greenhouse. One of the most disappointing things is to see a prize specimen suddenly keel over and die as a result of rot spreading out from the watery tissues round the central core of the plant. Three different types are common. Pythium is generally associated with the roots, and its presence should be suspected when sections of hitherto healthy root go brown and become easily detached from the main stock, accompanied by sudden rot or wilting. Rhizocionia attacks the part of the stem which joins the root at soil level and for this reason it is as well to guard against water, in which fungal diseases thrive, lying for any length of time round this danger point. Fusarium is also sometimes found. The best method of avoiding this is the use of sterilized pots and composts, and the regular use of systemic fungicides. It may be a wise precaution to dip new
From seed. Most commercial growers raise their cacti from seed. This is not always a reliable means of propagation as cross hybridization occurs fairly readily between members of related genera and cacti are generally self-sterile so that it is necessary to have two separate plants in order for pollination to be effective. The seed should be harvested while the pod is still intact and stored in a small envelope in a sunny place, allowing it to ripen of its own accord. When the pod has burst open and the seeds are reasonably dry they should be separated from the husk of the berry in so far as is possible and mixed with a small quantity of dry sand. Seed trays are best prepared by filling with a mixture of two parts sterilized loam, one part of peat, one part of coarse sand and one part of fine grit or shingle. A little lime may also be added. The tray should be filled in such a way that there is a slight mound in the centre to assist drainage and the whole should then be dipped in
a solution of benomyl to assist in sterilization. The seed-sand mixture should then be sprinkled lightly over the surface and a sheet of glass placed on top. No water should then be needed until the seedlings show through after a period which varies from three days to three weeks. Bottom heat is a useful asset and if a propagating unit is available this is a great help. Watering should be done often and lightly until the spines start to appear in the case of cacti or until characterization starts in the case of other succulents. Algae are the main problem at this stage and one of the best cures is to spray with a weak solution of copper sulphate at the rate of 1 cc per litre. Seedlings of all kinds should be transplanted as soon as they are big enough to handle and successive transplants should be made until the plants are big enough to go into a pot; this may not be until the end of their second year of growth. There is some evidence that parodias, which are very hard to raise from seed even when given the best possible conditions, can be more easily germinated if the seeded trays are kept in a dark place such as an airing cupboard.
From cuttings. Although seed is the fastest way to build up a large stock of a species it is a much slower process than taking cuttings. Cuttings of all succulents should be taken in the spring if possible as this is the time at which the plantlet is best able to adjust to its new environment and to develop a root system and start growing. The autumn is another possible period since roots may develop in time for growth in the spring. Cuttings may be taken at most other times, although the winter drought period does present some problems, and offsets of certain cacti, such as Nolocaclus ononis and Man/millaria zeitmanniana, should be struck regularly if possible as an insurance against the failure of the parent plant due to fungal diseases.
When taking a cutting, particularly from cacti and other succulents which have pronounced joints, avoid putting the end of the broken-off joint into the rooting mixture. Although the joint should be severed cleanly at such a branching point, the cutting should then be cut once more across the broadest part to enable as wide a surface as possible to develop roots. In this way a large healthy root system is formed. In the case of opuntias and leaf cacti this is particularly important as both species need considerable support from their root systems as they attain some size. Some genera, notably Kalanchoe, develop adventitious buds or plantlets on the edges of the leaves. These subsequently detach themselves and form their own clumps round the base of the parent plant and can later be potted up and grown on. In some species with adventitious buds, miniature root systems may even be formed while the plantlets are still attached to the main stem.
Cuttings are the most reliable means of increasing the number of a particular species but they also tend to disfigure the original plant. They are the only means of increasing cristate or monstrose specimens which rarely flower in cultivation and which, even when they do, normally have to be a considerable age. Moreover cristate specimens will not necessarily come true from seed. Such varieties tend to do better when grafted as their own rootstocks are inadequate to support extensive growth, and grafting is not difficult provided sterilized tools are used and some form of propagation unit is available.
Grafting. The part to be grafted is normally called the scion and the rooted part which forms the base of the combined plant is generally called the stock. Pereskia aculeaia is normally used as grafting stock for Rliipsalis and Zygocaclus and other epiphytic hanging species, although staking may be required as extra support. Other varieties may be grafted on to Trichocereus species as this is a robust variety. Hylocereus and Myrtillocactus stocks although cheap are not entirely satisfactory as both species require higher winter temperatures if they are to survive unharmed, and this may not always benefit the scion.
The stock and scion should be prepared by slicing through the stem of each so as to leave a roughly equal surface area on each which can be bonded together fairly easily. The stock should then have the ribs tapered away so as to ensure that any condensation which accumulates round the grafting point will drain away. A light application of benomyl brushed over this point will help to prevent infection creeping in. The stock and scion should then be joined so that the central core of each is in contact and this should be secured by using one or two long cactus spines from any species. When the union is effected the cactus spines can then be withdrawn.
It is a good idea to surround the stock and scion with a small polythene bag, completely covering the union and fixed round the stem of the stock with an elastic band; this should be left in place for about three weeks, during which time the plant is best kept in a propagation unit, and after this period the bag can be taken off and the joint examined very carefully. If union has still not taken place the covering should be replaced for another three weeks, after which time if union has still not occurred the exercise is likely to have been a failure.
Generally speaking succulents need normal watering throughout the summer months, during which period it can hardly become too hot for them provided a reasonable degree of air circulation is maintained. From
September to March the true cacti should be dried out completely and will need low temperatures round the 7°C (45°F) level, while the succulents will need slightly higher temperatures. Before implementing these very general instructions the reader should consult the relevant section describing each species in detail as some have a completely different regime.
The most conspicuous features of the semi-desert environment are air, light, and warmth, and all three are essential for successful cultivation. It is not worth trying to grow succulents in a greenhouse if it is unheated or if it is overshadowed by tall trees; in the latter case the cacti will be reluctant to flower and the succulents will grow weak and long and leggy. Water should be given thoroughly: let the surface of the compost dry out and then allow three days for a 2^-in (6-cm) pot or a week for a 4-in (10-cm) pot or bigger to elapse before plunging the entire pot in water and allowing it to stay there until the bubbles stop rising. Where this is not possible, as in the case of a large collection, do make sure that the plant is well watered. Failure to water thoroughly causes parts of the soil which remain dry to turn sour and this enables fungi and bacteria to take root
Although a common feature of flower shops and garden centres the cactus garden as commonly known to commercial horticulture should be avoided. Because of their somewhat different watering requirements, succulents other than cacti tend to need watering once every three weeks or so during the winter, thus cacti and other succulents generally make poor companions in the same bowl. The tendency to put chippings on top of the soil can also present problems as it prevents effective aeration of the soil. The best idea is to plant bowls of cacti or bowls of succulents and rely on rocks to provide the necessary variety in shape and texture where this cannot be achieved with the correct
Having outlined the chief botanical distinction between the cacti and other succulents, the main cultural differences are that cacti will generally tolerate lower winter temperatures and need considerably less water in this period than other succulents. There are, of course, exceptions to this as there are to any rule, but in the absence of information to the contrary cacti require a maximum temperature at nights of 7°C (45°F) in the winter and need to be kept completely dry between the end of September and mid-March. Other succulents generally prefer somewhat higher winter temperatures round the 10°C (50°F) level and consequently more regular watering, probably as often as once every four weeks. Do not stake cacti unless absolutely necessary as this tends to weaken them permanently, often an unstaked but floppy cactus or any other succulent will straighten itself and become stiffer with time. 97
The arrangement of plants in this book is partly botanical and partly based on appearances. If you have a named plant the best idea is to look it up in the index and then refer to the appropriate page; but if, on the other hand, you have a plant without a name the following guide to the arrangement of genera in the book may assist you to find it.
First check whether the plant has a woolly or bristly pad below the thorns if it has any, or even, in the absence of any thorns, merely a woolly pad. If the plant does have areoles then it may be found between pages
100 and 164. If it lacks these il should be in the following pages.
The first group of cacti described on page 100 are easily distinguished by the presence of conspicuous and quite normal leaves. They are one of the most primitive groups of cactus and are^alled Pereskieae. 
101 and 107 are the prickly pear type, distinguished by the presence of glochids or easily detached and frequently somewhat painful bristles buried amongst the spine cushions. They are in turn subdivided into two distinct groups. Those more characteristic species with flat-jointed stems are illustrated and described between pages 101 and 105,  while those with round stems are dealt with on the following two pages.
The remainder of the family have been allocated to a very large group called Cereanae, which have neither leaves nor glochids and comprise the majority of cactus species. This large group is in turn divided into several sub-groups as follows.
First the candelabra-type or upright cylindrical cacti called the Cereeae, which is derived from the Greek word for a candle. These are illustrated on pages 108 to 118 and are distinguished by their generally somewhat thin cylindrical shape and a reluctance to flower when young (3], Wilcoxia schmollii is a notable exception here which has pendulous stems, and Carnegiea gigantea, although one of the largest and most typically branched of the group when mature, has a somewhat rounded globular appearance when young.
The Hylocereanae are the more sprawling cacti, tending to be fast growers making adventitious roots which batten on to trees and rocks in the wild. They are somewhat freer flowering than the previous group and appreciate a little more warmth in winter. See pages 119 and 120. 
Then follow two groups of hedgehog cacti; the Echinocereanae (pages 121 to 128) are generally barrel shaped although some may become somewhat cylindrical, and are distinguished by the production of flower buds from the previous year's growth on the sides of the stems. They comprise some of the most easily flowered genera such as Rebutia and Aylostera.  The Echinocacianae (pages 129 to 147), on the other hand, produce their flowers at the top of the plant and the flowering areoles are unfolded with the non-flowering ones each year from the centre of the plant. 
The Caclanae consists of one genus Melocactus, page 148. The distinguishing feature of this group is the production of a large cephalium or woolly crown at the top of the plant just before flowering. These plants are all somewhat rare in cultivation and it is unlikely that an unnamed variety belongs to this group. Generally they require rather more warmth in winter. 
The previous groups have all been characterized by the production of flowers from the areoles, or spine clusters. The Coryphanthanae are tuberculate plants whose flowers are produced in the axils between the spines. I have included here the Thelocacti although they do not flower in this fashion because of their extreme resemblance to the Coryphanthanae and because of their general reluctance to flower when young. The Coryphanthanae are described on pages 149 to 160. 
Tho last twn oro-ps of cacti described are the Epiphyllanae, illustrated on pages 161 and 162, which produce mainly flat leaf-like stems,  and the Rhipsalidanae described on the following two pages which, with the exception of Rhipsalidopsis rosea (a bigeneric hybrid anyway) and Rhipsalis houlletiana, produce angled or cylindrical stems. 
The remaining succulents can be broadly classified according to their habit. Those which lack areoles and exude a milky sap when pierced are members of the Euphorbiaceae described on pages 165 to 169 (plants which have areoles and a milky sap are probably mammillarias described on pages 157 to 160).  The remaining succulents other than cacti have been subdivided into the 'living stone' group, having generally little or nothing in the way of stems and a pebble-like or chunky appearance. These are all members of the Aizoaceae and are described on pages 170 to 173. 
Pages 174 to 178 are devoted to those succulents which have little or no stems and form instead rosettes or clumps of leafy growth. 
In contrast, those succulents with upright, arched or hanging stems are described on pages 179 to 188  and are drawn from a wide variety of genera, those with upright stems described at the beginning of the section and those with hanging stems described near the end.
Opposite. A guide to the identification of the groups of cacti and succulents which appear in this book. The types of plants are given in order left to right and top to bottom to correspond with the text on this page
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