All 20 genera of this subtribe are esteemed by cactophiles, and the majority are solitary or form compact mounds of heads, and accommodate well to small . pots in a glasshouse. Taking the largest-growing first. Echinocactus (6.11) and Ferocaclus (2.1. 16.29) are the "barrel cacti", conspicuous features of the drier areas of Mexico and the southwest USA. But even though potted specimens need to be large before flowering, the plants are valued for the superb spines, often hooked in Ferocaclus and marked with transverse bands; the colour intensifies on wetting. F. fordii and F. viridescens will bloom in a 12cm (5in) pot.

Thelocactus is an ill-defined genus but includes many desirable species such as T. nidulans, whose stout, grey, flaking spines surround the outside of the stem like a bird's nest (16.30). The obvious feature of all but one species of Echino-fossulocactus is the large number of very thin wavy ribs, which make it distinctive and readily recognizable. Astrophytum, composed of only four species, is a case of

"once seen, never forgotten". The stem branches only if damaged, and has a few deep, acute ribs more-or-less covered with white flecks, giving a snowy effect. Two species, A. myriostigma( ¡6.31) and A. asterias. lack spines. A. ornatum is the largest-growing (16.32) and needs to be in a 15cm (6in) pot before flowering; the others flower more freely, and I have had A. asterias oblige in the second year from seed. A. capricorne, with soft curling spines, has the best bloom of all, fully 7cm (2%in) across and bright clear yellow with a red throat. Propagation is by seed. The species are self-incompatible, and there are many intriguing hybrids.

Also distinctive at first sight is Copiapoa cinerea, with a greyish white, pruinose body contrasting with stout dark central spines. Cymnocalycium, with around 60 species from South America, is often made the subject of a specialist collection to itself (16.44): as with Mammillaria, the discerning eye can find endless pleasure in the subtle differ-emces of tubercle shape and spiralling, body colour, and number and disposition of spines. Many of the flowers are a sombre off-white colour, but some are yellow (G. andreae). red (G. baldianum) or lilac (G. horridispinum). Characteristic features are a chin-like bulge to the tubercle below each areole, and the broad, rounded scales on the flower tube, without any hairs or spines. Right(t6.29): Ferocaclus acanthodes tortulospinus about60cm(2f0 tall in Baja California The long twisting spines are its most noteworthy leature

Far right (16.30): Thelocactus nidulans also has a nickname Birds Nest Cactus' trom the "nest" of grey librous spines thai surrounds an old plant The plant remains solitary and is propagated by seed

Below (16.31 J: The spineless Astrophytum myriostigma in habitat in San Luis Potosi associated with bromeliads. The popular name is Bishop's Cap Cactus' Astrophylums are typically covered in white tlecks

Below right (16.32): Astrophytum has only lour species, but all are easily recognizable and have long been firm favourites in is the largest growing, rophytum ornatum, and one of the two

Lophophora Yellow

Leuchtenbergia principis (16.35) stands all by itself, with the longest of tubercles surmounted by long, flattened, papery spines. The impressively large yellow flower arises near the centre from the tip of a young tubercle. Aztekium ritteri is another oddity, in which the squat olive green stem is covered in horizontal creases giving the impression of great age. Lophophora is one of the few spineless cacti, its soft, grey, top-shaped body bearing a tuft of wool from each low, rounded tubercle. There is a single variable species L. williamsii(2.3,16.34), although some botanists recognize a second. L. diffusa. The small white or pink flowers are self-compatible and set plentiful seed that is easy but slow to raise. This is the famous peyote (peyotl) of the Mexican Indians, and its ritual uses are discussed on page 18.

Ariocarpus looks even less like the conventional idea of a cactus. Its six species grow with the conical body buried in the ground, exposing only a flat rosette of tough, pointed or truncate incrusted tubercles (16.33). In habitat one can walk over them without either noticing or harming them. In cultivation it is wise to plant the body half way out of the soil to minimize the danger of rotting. From seed Ariocarpus is slow and takes many years to reach flowering size. Grafting can effect a remarkable growth acceleration. but produces a globular, untypical specimen. Contrary to earlier belief, A rio-carpus takes plenty of water in the summer, provided that it is well rooted

Below[ 16.33): Ariocarpus retusus is hard to see in habitat, lying flush with the ground and partly covered in soil The plant has a tuberous root and is very slow growing

Above(l6.34): Lophophora williamsii. the peyote or"LS.D cactus'' referred to on page 18. In place of spines, the areoles produce a shaving brush of hairs

Right(16.3S): Leuchtenbergia principis differs from all other cacti in its triangular tubercles, which grow up to 10cm (4in) in length, and in its soft, papery white spines

Cactus Fleshy Tubercles

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and (hat sun and ventilation are maximal. Past losses have mainly arisen from damaged imported plants, which root slowly or not at all.

Epithelantha species and Pelecyphora (16.38) are neat miniatures of slow growth, covered in spiral tubercles with many short spines at each areole. In Pelecyphora asclliformis the body is grey and each areole is long and narrow with spines in two rows pointing in opposite directions —rather recalling a woodlouse viewed from above. P. slrobiliformis has flat, incurved, overlapping tubercles like a pine cone. Strombocactus (taken here to include Obregonia and Turbinicarpus) and Pediocactus (embracing Navajoa. Pilocanthus, Toumeya and Utahia) include further collector's gems, mostly content with 7-9cm (3-3'/4in) pots and a cool, dry, light top shelf in winter. Those from the southwest USA are mostly difficult to keep and best left to specialists: Pediocactus sileri. P. paradinei (16.39) and P. knowltonii, for instance. Those from Mexico are more accommodating, trouble free, and among the earliest cacti to bloom in spring. Strombocactus denegrii (16.36) resembles an Ariocarpus in body form.

Neolloydia (16.37) from Mexico and Escobaria from further north into the USA comprise additional dwarf tuber-culate plants having a conspicuous groove on the upper side of the tubercle leading

Right (16.36): Strombocactus (Obregonia) denegrii never ottsets and is raised onlytrom seed Notice the leal-like tubercles and woolly crown. II comes from Tamaulipas in Mexico.

Below right (16.37): Neolloydia conoidea (syn N. texensisj from Texas and Northern Mexico eventually forms clumps. It thrives in lull sun and flowers over several weeks Below(16.38): Pelecyphora asellitormis is readily recognized by the hatchet-shaped tubercles and comb-like spines Plants rarely exceed 5 cm (2in) in diameter.

Above(16.39): Pediocactus paradinei is rare in habiial and rarer in cultivation: a challenge lor connoisseurs who like "difficult" species This specimen is 4cm(iy,in) across the body.

LeH( 16.40): Coryphantha vivipara in habitat in Salida, Colorado. Il is widespread in the USA and hardy, reaching almost )o the northern limits ol Cactaceae from the areole to the axil. This is also clearly seen in the large genus Coryphantha (about 60 species), where the tubercles are large to very large. Although it is less free-flowering than some genera, the blooms are usually worth waiting for. C. vivipara (16.40) is frost hardy, and bears freely its eye-catching violet-magenta flowers followed by large, fleshy green berries.

Finally we come to Mammillaria, with over 225 species, second only to Opuntia in size and to none in popularity. From Mexico it extends north into the USA, east to the West Indies and south into northern South America. All are dwarf, solitary or clustering cacti with tubercles arranged in conspicuous spirals tipped by a group of spines. The main diagnostic feature is that innovations —new shoots or flower buds—arise from the base of the tubercle, not at its tip. The flowers are usually small but borne profusely in rings like a garland around the apex of the stem (16.42), and are succeeded by smooth, elongated, fleshy, usually red berries, which are a colourful sight in autumn (7.3). They are edible and have the native name "chilitos". Of spines.

there seems no limit to variations (2.14): straight or hooked, variously angled, comb-like (pectinate) in M. pectinifera. feathered (plumose) in M. plumosa and M. pennispinosa. and so on. Some species exude drops of milky white sap when cut. Culturally they cover the whole range from easy-growing, almost hardy species such as M. magnimamma to others that are preserved with difficulty, usually as grafts, and hence keep the specialists on their toes. With so many desirable species a selection is almost too personal to venture. M. guelzowiana (16.41), M.

boolii (16.43) and other large-flowering species are favourites, especially when the plant body itself is very tiny (M. theresae and allies). M. zeilmanniana is mass-multiplied for the market for its profuse magenta flowers. M. hahniana and M. plumosa look as if wrapped in

Propagation is by seed, division of clumps, or cuttings. A few species seed themselves in the glasshouse, and under favourable conditions I have had M. bocasana in flower within a year of germination. It is no accident that

Mammillaria earned a society to itself, founded in the London area in 1960 and publishing a quarterly journal.

Right (16.41): Mammillaria guelzowiana is treasured lor its silky white hair and large blooms. Bui it needs carelui watering.

Below right (16.42): Mammillarias appeal by their diversity ol tubercle patterns, spinalion and tlowers in rings round the stem.

Below (16.43): Flat-topped and llush with the soil in habitat in Sonora. Mammillaria boolii changes form when cultivated The5cm(2in) ttower is one olthe largest in the genus

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