Here we come upon plants more typical of tropical forest regions than semi-deserts, and adapted for life as epiphytes or lithophytes. The stems are typically long and flexible—many metres in some —and, except in Aporocactus. have few

Right (16.19]: Lobivia densispina flowering in a 6 cm (2Viin) pot Like Rebutia. Lobivia is a good genus lor beginners and flowers freely on small specimens.

Below (16.20): Rebutias set seed readily in captivity but Ihe seed is olten hybrid For pure seed, hand-pollination of Iwo plants ol the same species is needed

ribs. They put cuit adventitious roots into the air, which assist in water absorption and, when they contact suitable surfaces, take hold and support the plant. The spines are mostly minute or hardly developed at all. The flowers range from the smallest to the largest in the Family.

Some root in the soil (Hylocereus, Selenicereus) and ascend high up tree trunks or rock faces much like ivy clinging to a wall. Eventually, contact with the ground may be lost by the death and decay of the primary root. Others grow naturally hanging from steep rock faces (Aporocactus, Morangaya) or from the boughs of forest trees (Epiphyllum. Nopalxochia. Rhipsalis 4.18) in the same way as do orchids and bromeliads. with which they often keep company. Nourishment comes from windblown humus that falls amid the stems and decomposes.

Aporocactus, with about five similar species, includes A. flagelliformis, the celebrated 'Rat's Tail Cactus' that has long adorned cottage windows and is one of the hardiest and most tolerant of all cacti. Although introduced to Europe as early as 1690 its native habitat remained unknown until a few plants were located in the wild in Mexico within the past 20 years. The flowers of this genus are oblique, being slightly S-shaped in

Heliocereus is a small genus of more erect growth in cultivation, although scrambling or climbing in the wild. The elongated stems have from two to seven wings, and the flowers are large, regular, and mostly red, and open by day. The best-known is H. speciosus (16.22), parent of the hybrid epicacti (page 72), to which it contributes the brilliant vermilion of the petals with a steely blue flush along the inner margins. There is a pure white form, and H. cinnabarinus is the colour of cinnabar.

Hylocereus consists entirely of epiphytes, which usually start at ground level and form great canopies hanging from trees, climbing to a height of up to 10m (33ft) by means of their sturdy, three-winged, long-jointed stems with copious aerial roots. They are essentially plants of the tropics, needing ample root room, water and warmth. In a suitably large glasshouse a Hylocereus can be trained on wires to hang from the roof, where it will reward the grower by its marvellous large white flowers, which open at night and are powerfully scented. They are followed by large fleshy fruits.

Top left(16.21] Rebutia marsoneri from northern Argentina. Flower colour in Rebutia is red or yellow, sometimes orange, pink, purple or

Left (16.221: Heliocereus speciosus. one of the parents of the epicacti. to which it transmits day- opening along with the vivid red and steely blue Hush of the flowers

Top left(16.21] Rebutia marsoneri from northern Argentina. Flower colour in Rebutia is red or yellow, sometimes orange, pink, purple or

Left (16.221: Heliocereus speciosus. one of the parents of the epicacti. to which it transmits day- opening along with the vivid red and steely blue Hush of the flowers

Selenicereus differs in having slender cylindrical stems with from three to ten low ribs, and a more slender flower tube covered with tiny scales and felt instead of the large scales of Hylocereus. It now includes plants formerly segregated as Mediocactus and Deamia. The largest and most gorgeous of all cactus flowers are found here in S. megalanthus and S. macdonaldiae. up to 38cm (15in) long and 30cm (12in) in spread. The best-known is the original 'Queen of the Night', S. grandiflorus, from Jamaica, cultivated since 1700. Although nothing to get excited about when not in flower, a Selenicereus takes up little space if positioned at the back of the staging and trained to fill in corners. The floral display is all the more breath-taking for appearing on such unpretentious stems.

Epiphyllum species are epiphytes, rarely growing at soil level and more at home in crotches of the branches of trees, often many metres above the ground. The flattened green branches with tiny areoles and few or no bristles are often mistaken for leaves. The margins are variously notched or lobed (E. anguliger) or, in one species (E. chrysocardium), so deeply incised as to look like the frond of a cycad. The flowers are white and nocturnal, with a long narrow tube. E crenalum is one parent of the epicacti (5.11, 12) Nopalxochia (16.23) is a related genus, whose flowers are pink (N. phyllanthoides) or red (TV. ackermannii).

Schlumbergera includes another great favourite of cottage windows, the 'Christmas Cactus', variously labelled Zygo-cactus truncatus and other names, but correctly Schlumbergera X buckleyi. a hybrid descended from S. truncala X S. russelliana. The plant consists of chains of short, flat, green, leaf-like, unarmed stem joints with rounded notches and bears terminal almost regular flowers about 7cm (2%in) long. The true S. truncala is less common, and has more pointed teeth on the stem segments and a very oblique corolla.

Rhipsalis is one of the largest genera in the Cactaceae, and perhaps the most varied in general habit, showing remarkable diversity in the lengths and geometrical arrangements of the jointed stems. These may be flat, cylindrical, angled or ribbed, often assembled in whorls and of different shapes on the one plant. Spines are absent or fine bristles on young growth only. The flowers are very tiny and white, pinkish or yellow, but make up in number and, in some species, by appearing in winter—a welcome novelty. They occur all along the hanging stems and are followed by small juicy berries: "mistletoe cactus" is the

Right (16.23): Flowers ot Deutsche Kaiserin', a cultivarol Nopalxochia. which has Hat leallike stems and no spines Nopalxochia species grow naturally as epiphytes in Mexico.

common name of species with white fruits (4.18). Rhipsalis species make excellent basket plants and their neglect by collectors is hard to understand. Two species are, however, well-known and exceptional for producing larger, colourful blooms: R. gaertneri, the 'Easter Cactus' (page 179), with vivid vermilion flowers, and R. rosea with pink ones.

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