More books are written about cacti than all the other succulents put together, and some add a final injustice by including a chapter on "other succulents" rather as an afterthought. Indeed, the very word "cactus" has been taken over by the general public for any fleshy, prickly, bizarre-looking plant: a sad distortion of its botanical meaning as a member of the Family Cactaceae.
The reasons for the popularity of cacti are not hard to find. First, they all look so different from other plants: the general lack of leaves, the spikiness, the geometric patterns of spines, tubercles and ribs— these, although matched by isolated African euphorbias, pachypo-diums and didiereas, set them in a Family by themselves. Second, they are ideal collectors' pieces: a majority not too difficult to obtain and keep, a minority offering just that challenge that inspires the perfectionist and connoisseur. On this balance of factors collectormania
Then again, cacti have a remarkable tolerance of neglect, looking after themselves while the owner goes on holiday or recovers from influenza, yet they respond wonderfully to good management and hence are well fitted for the exhibition table at flower shows. Flowering isalways something of an event: although not half as rare as some believe, it usually covers only a small part of the whole season, and when the subject is as spectacular as the "seven hours' wonder" of the night-blooming cerei, it is an occasion for calling in the neighbours and uncorking the champagne. Yet the plants are attractive all the year round, even if they never flower, which cannot be said for roses and many other garden favourites.
Classification of cacti The name Kaktos occurs in classical literature, being used by Theophrastus for the prickly cardoon (CynamJ. However, it was taken up in 1753 by Linnaeus as a genus. Cactus L„ in which he placed all the then known 22 species of cacti. Linnaeus was ultra-conservative, and his 22 species are today referred to 12 separate genera. But the generic name Cactus is no longer used, because it invites confusion with the cactus of common parlance, which is any member of the whole Family. The dictionary, by the way, allows both plurals: cacti and cactuses, but only the former has come
Nineteenth-century studies of cacti culminated in a monograph by Karl
Schumann, who in 1903 recognized 21 genera and 760 species. This is still a classic work, and a model of thoroughness and moderation in a Family that has proved exceptionally difficult to classify. The twentieth century saw many new systems, mostly radical, from that of Britton & Rose in 1919-23 to that of Backeberg in 1958-62 with over 300 genera and over 2,000 species. In absence of a more conservative treatment, Backeberg is followed by many, but for the synopsis of genera here the basis is a review by D. R. Hunt in Hutchinson's Genera of Flowering Plants Vol. II, 1967, where the total of genera is reduced to 84.
The garden history of cacti is no less topsy-turvy than their taxonomic history. The first specimens to reach Europe in the sixteenth century came from the West Indies, and it so happens that no cactus is more difficult to establish after uprooting than a mature Melocactus. The impression arose that all cacti needed great heat, and later arrivals from less tropical regions were assigned to the stove house and given next to no water, a soil devoid of all nutrients and inadequate lighting.
The most widely publicized of cacti are those of the southwestern United States. Everyone is familiar with the giant saguaro (Carnegiea 5.7) and prickly pears (Opuntia 1.7) of Arizona through Hollywood westerns, Disney epics, schoolboy penny dreadfuls and literature from tourist brochures to highly respected picture magazines such as Arizona Highways. Mention a cactus to many folk and this is the image that at once springs to mind. Yet, surprisingly, these are the cacti least seen in European collections. Carnegiea is so subtly adjusted to life in the southwestern drylands that it languishes away from them, and in any Right(16 I): Echinopsis (Trichocereus) spachiana is one ot the most vigorous and easy growing columnar cacti, but needs to be a metre or so tall before blooming. II also makes one ol the best grafting stocks
Below (16.2): Lite lorms in Cactaceae Hal-and cylindrical- jointed Opuntias (right and centre! and columnar, ribbed Cereus(left}.
Leaves absent or microscopic
Glochids absent; seeds black, without an aril
Glochids present; seeds covered by a pale bony aril or winged Subfamily 2 OPUNTIOIDEAE
. black or brown, not covered by a bony arH
Subfamily 1 PERESKIOIDEAE
• less columnar (cereoid) with usually few-ribbed, or, if dwarf, then flowering from the old areoles Tribe 1
Habit m jointed :
Terrestial plants without aerial roots; spines usually conspicuous
Receptacle tube thinly hairy or rarely naked, narrow-scale Subtribe 2 ECHINOPSIDINAE
Receptacle tube naked c armed, sometimes scaly Subtribe 1 CEREINAE
Subtribe 1 CEREINAE
Subtribe 2 ECHINOPSIDINAE
Subfamily 1 PERESKIOIDEAE
(CACTACEAE)—A breakdown to genus level
THE CACTUS FAMILY
Pereskia. with its large leaves, is regarded in Cactaceae as a link with the past
case flowers only when some metres tall. Many dwarf United States cacti, although attractive to collectors, do not adapt well tocountries with moist summersand less intense sunshine. It is from Mexico and South America that most of the collectors' cacti come, and these did not reach Europe in any quantity until well into the nineteenth century.
In the past two or three decades there has been a veritable flood of novelties as new roads push ever deeper into Brazil. Peru and Chile: Nolocactus. Neoporteria. Parodia and Gymnocalycium by the dozen, and new genera such as Uebel-man ma and Buiningia. Although many of these occur south of the Equator, they acclimatize better to the reversed seasons of the Northern Hemisphere than do the desert species of the U.S.A. (see page 74). Today they are firm favourites, but the old myths of starvation diet, small pots and intense heat linger on and are slow to disappear.
What makes a cactus?
The Cactaceae are perennials ranging in stature from tiny button-sized Bloss-feldias to candelabra Pachycereus (16.3) and Camegiea up to about 10m (33ft) tall and weighing many tons. Pereskia is tallest of all, forming forest trees up to 24m (80ft), and is considered the least specialized, being sparingly succulent and bearing large, expanded, semi-persistent leaves. In the remainder, the functions of leaves are transferred to the thick fleshy stems, which are green when young although they become woody with age. Leaves are absent or, in the Opuntioideae, reduced and more or less scale-like. The stems are typically ribbed and star-like in cross-section, or covered in tubercles in straight or spiral rows. Most cacti have spines, and these arise, as do the branches and flowers, from special felted cushions called areoles (2.14, 15), which may be regarded as telescoped lateral branches (spur shoots)
in which spines represent all that remains of undeveloped leaves.
The flowers are solitary (rarely two or more from an areole) and sessile (that is, without a stalk), Pereskia again being exceptional. The numerous bracts, sepals and petals are spirally arranged and typically show a transition from one to the other (16.4)—a very primitive feature. They are more or less united to form a tube, which may reach 30cm (12in) in length in the Hylocereinae (2.17). The stamens are also numerous and spiralled, arising from the inner wall of the tube, and surround a single style with branching stigma lobes at its tip. Flower colours run from white through yellow to pink, orange, red and purple; blue is absent. The inferior ovary often bears areoles on its outside with spines, bristles and wool, and ripens to a juicy "berry", although there are transitions to a dry. dehiscent capsule. The seeds are usually black and have a curved embryo within.
The Cactaceae have no close relatives and for a long time defied efforts to fit them neatly into systems of classification. Now they are well sited in Caryophyllales alongside Phytolaccaceae. Portulacaceae and Mesembryanthemaceae. with which they share many less obvious features including the pigment betacyanin. They are exclusively New World plants, most highly concentrated in the dry mountainous regions on either side of the Equator, but extending north as far as Canada and south to the tip of South America. Elsewhere they have been introduced and naturalized.
Right (16 3) Pachycereus pringlei in habitat in Ba/a California, where it is the counterpart ol the giant saguaro (Carnegiea) in Arizona
Below (16 4) Pereskia grandifolia llowers Ireely on a small plant in a 12 5cm (5in] pot,
Pereskia. with its large leaves, is regarded in Cactaceae as a link with the past
If Pereskia did not exist, it would have had to be invented to explain the missing link between cacti and their mesophytic ancestors. This is not to assert that it is in the direct line of descent of the other, more advanced genera. Rather it is a survivor, an early offshoot of the family tree, which by remaining within the moist tropics has evolved fewer specializations for desert survival. Not all Pereskia characters are unspecialized: the advanced areole and spines are already present in all species. As tall shrubs and trees the species are usually seen away from habitat only in botanical gardens, but the best-suited to pot culture is P. grandifolia (16.4), which produces its showy pink flowers, like single dog roses, in a 12cm (5in) pot. P. aculeata (page 178) is the commonest species and its long branches climb by means of stipular prickles: a hooked pairat the base of each leaf. Pereskias require a rich soil and much warmth—a winter minimum of
Right(16.5]: Pereskiopsis has the flat leaves and shrubby habit ol Pereskia but a /lower and fruit that have more in common with Opuntia. In collections it is most valued as a graiting stock for accelerating tiny seedlings
10°C (50°F) at least-and will take plenty of water in summer, less in winter.
The pictures of Opuntia (16.7) give a good idea of the general look of this subfamily, where the stems are characteristically long- or short-jointed and sometimes tuberculate but hardly ever ribbed. Leaves are rarely flat (Pereskiopsis, 16.5), more often cylindrical. In Opuntia subulata they can.be up to 12cm (5in) long and fairly persistent, but that is exceptional. Mostly they are tiny scales that quickly wither and fall, and perform no useful function in photosynthesis. Seedlings have two conspicuous flat cotyledons.
Spines are present, and also glochids: smaller, bristle-like spines with recurved barbs like a bee-sting that detach readily and make these the most unpleasant of all succulents to handle.
Pterocactus has a large winged seed; in others the seeds are also quite big and covered in a bony shield called an aril. which makes them slow to germinate.
Of the four small genera, the only one that need be mentioned here is Pereskiopsis, which is an excellent grafting stock for tiny seedling cacti, although too tender to recommend for a permanent
By contrast, Opuntia is the largest and most widespread genus of the Cactaceae, extending from Canada to Patagonia — the limits of the Family. It thus includes the hardiest of cacti, a few of which can be successfully grown outdoors in northern Europe. Three subgenera are recognized
on the shape of the joints: Cylindropuntia
(16.6) with cylindrical stems and branches, Tephrocactus (5.5) with globular or ellipsoidal joints, and Opuntia
(16.7) with flat, disc-like pads. These are treated by some as separate genera.
Most opuntias are too rank-growing for a small glasshouse. A single pad of O. vulgaris (monacantha) stuck in a bed of the cold section of my glasshouse grew to eight pads the first year and 64 the second, when it had to be taken out for fear it would break the glass. Also they mostly need to be large before flowers can be expected—a pity, because the blooms are extremely beautiful (4.1) and have sensitive stamens (page 54).
Subgenus Cylindropuntia occurs both north and south of the Equator. The North American species have sheathed spines (16.6): when a spine is touched, the barbed sheath sticks in the skin and slides off like a glove finger, leaving the spine itself on the plant. For those with space problems, I recommend the slowest growing species. O. pachypus. of which there is also an attractive cristate form. O. invicta has short joints and huge dagger-like spines.
Subgenus Tephrocactus includes mostly smaller plants of great diversity in shape and spination of the joints: their principal attraction in cultivation as flowers are sparse. Despite the existence of a good handbook by Leighton-Boyce and Iliff, the plants are not as widely grown as they deserve.
Subgenus Opuntia introduces that Jekyll-and-Hyde plant, the prickly pear, hated as a weed in Australia where it has infested large areas of farmland, but cultivated in other countries for its fruit or as cattle fodder. O.(Nopalea) coccinell-ifera is the principal host plant for rearing a scale insect that is the source of the red dye cochineal, although nowadays a synthetic dye is cheaper substitute. Opuntia finds a further use as hedges: woe betide anyone who tries to get through one!
Those accustomed to see opuntias as tiny specimens cramped in pots have no idea what a splendid effect they make when well grown in the open. In Europe the best display I have seen is nearBlanes in Spain. But no collection, however
Below (16 7): Opuntia vulgaris, the prickly pear, in llower and with unripe Iruits Opuntia is naturalized in many places outside the Americas,■ this was photographed in Kenya c ra mped. should be without one or two. If the glochids are a deterrent, there is even one— Opuntia microdasys 'Albatus'— where the bristles are so soft that it can be handled with impunity.
Cereinae. like Opuntioideae. include some largish plants that look their best and flower only when given space and room for their roots. In a glasshouse collection they can stand at the back of the staging, or larger ones can go at floor level, making a foil for the globular types. If planted out in a bed their sturdy growth and improved spina tion will be a surprise to those used only to pot culture.
Cere us. with a massive candelabra of few-angled stems and large, white, nocturnal flowers with only a few scales on the tube, is a genus of great adaptability. It tolerates temperatures from tropical heat to near freezing, and seems equally indifferent to excess or deficiency of water. Although native to South America, some of the species (there are several, all very much alike) grow successfully outdoors in many warmer countries (6.9), and often reach a large size. Monvillea is smaller in all parts and better tailored for the amateur's glasshouse. Cephalocereus is one of a number of genera in which the onset of flowering leads to a great development of hairs orbristlesat or near the stem apices: a cephalium. as it is called (16.10). We shall encounter many variants of cephalia: terminal, lateral, or in between the two. In C. chrysacanthus the flowering stems develop extra wool all round; in C. brevtcylindricus the golden cephalium is lopsided, suggesting the mane of a lion. This species has short stems, usually broader than tall, and has been put in a separate genus, Buinirtgia. Even more startling is C. (Backebergia) militaris, where the small flowers push out from a dense, golden brown, terminal cephalium. From time to time these tops of flowering stems have been cut off in habitat, imported and offered at high prices. Technically, they are inflorescences, not plants, and although they can be rooted, casualties are high, and subsequent growth either spoils the cephalium or consists of normal, barren shoots from beneath it. C. senilis, the 'Old Man Cactus', has for long been a favourite for its overall covering of shaggy white hairs (16.8). It is a slow-growing and sensitive to over-watering, so a well-grown sizeable plant will always be a treasure.
Pachycereus includes the giants of the candelabra cacti (16.3), a dominating
Above right (16.81: Cephalocereus senilis, the 'Old Man Cactus', is prized because olits slow growth. It needs caretul management, however, to avoid rotting and loss ol roots. Right(16 9} Pachycereus pecten-aboriginum gets its name from the very prickly, dry Iruit, which is tancilully called "aborigine's comb"
feature of any Mexican landscape where they occur. The fruits of P. pecten-aboriginum (16.9), are more bristly than chestnuts and, as the name implies, are supposed to be used as combs by the natives. I was not tempted to try them. This dry spiny fruit distinguishes Pachy-cereus in Mexico from its counterpart Carnegiea in Arizona. C.gigantea. the saguaro and sole species, is the State flower of Arizona and one of the most photographed and familiar of all cacti (16.12), although one of the least interesting as small pot specimens, which grow very slowly and never flower.
Carnegiea has a fleshy berry that is harvested by the Indians by means of long strips of wood obtained from the skeleton of the plant itself: the flesh is edible, and the seeds can be ground up for meal. Large areas where saguaros used to grow have now been urbanized, and the species is susceptible to various diseases and hazards, mostly attributable to man's activities. Because of its low regeneration, it has been much studied by ecologists and conservationists, and surviving populations are now protected or set aside as national parks (7.6).
The barren shoots are like those of Cereus, but when sufficiently mature they form copious brisdes at the apex and a terminal cephalium (16.11). But there is also a very different monstrous form beloved of collectors because of its scarcity and novel appearance, like a sculpture in jade, lacking spines and regular ribs.
Myrtillocactus seedlings are handsome pot plants on account of the bluish Beiow[l6.10): Cephalocereus (Neobuxbaumia) polylophus. the flowering lop ola3m( 10ft] 7en in a Calilornian garden. The solitary ; about 23cm (9in} thick
pruinose stems. They need to be large before they bloom. Seedlings can be used as grafting stocks, but are noticeably more tender than Echinopsis.
Lemaireocereus is a mixed-up genus taxonomically. but this is no place to elaborate the problems. The many species are noble columnar cacti characteristic of the drier areas of Mexico, where they add a distinctive look to the skyline. For the glasshouse grower some are attractive as seedlings, especially the choice and delicate L. betieckeicovered in a powdery white "bloom".
With Echinocereus we come to plants of dwarf stature, with solitary or clump-
forming columnar or globose stems, and mostly at home in medium-sized pots. The 70 species extend from Mexico up to the northern USA, where it is represented by the frost-hardy E. triglochidiatus (coccinetis), the 'Claret Cup', with brilliant red funnel-shaped blooms on five- to eight-angled stems, and E. viridiflorus. a dwarf solitary or few-headed species with flowers of varying yellowish shades, sometimes, as the name implies, distinctly green. Something of an oddity is the unarmed variety, inermis, of E triglochidiatus (16.14) that occurs very locally in Colorado: it is exactly similar to the species except for the almost complete lack of spines, yet holds its own in nature. Echinocerei are noted for the soft-fleshed stems, green and usually somewhat ribbed. The flowers range from small (E. davisii) to 10-12cm (4-5in) across, and can be yellow (E papillosus) orange (E salmdyckianus). pink (E amoenus).
Right 116.11): The barren stems ol Lophocereus schottii have distant areoles with tiny spines Only the flowering lops develop these bristles Two or more Ilowers
Below (16.12): Flowers ot the giant saguaro (Carnegia gigantea) crown Ihe tall stems in May and are succeeded by lleshy Iruits Notice the very large number ol stamens
purple (E caespitosus) or brownish (E chloratilhus) as well as green. The effect is made more dramatic by the contrast with yellow anthers and green stigma lobes. In cultivation I find that light is a more important factor in success than high temperatures—indeed, the mixed collection I keep in the south-facing end of my glasshouse seem none the worse for drops below freezing point in winter, provided I keep them quite dry. In summer they are watered freely as long as the weather is mild. Very little attention is needed.
E. pectinatus var. rigidissimus is the 'Rainbow Cactus' of Arizona, a beauty at all seasons from the consecutive bands of pink, white and straw-coloured spines up the stem. E knippelianus (16.13) is a miniature, with a soft, solitary, flattened, almost unarmed stem the size of a golfball. Some echinocerei produce large flowers when no more than 3cm (1 i/6in) high, whereas E. delaetii is one of the shy-flowering species, but much prized because its white shaggy hairs make it a miniature 'Old Man Cactus'.
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