A predominantly tropical Family, the Apocynaceae comprise about 180 genera and 1,500 species. They are mostly twining plants with a white milky sap (latex). The flowers are often quite showy and some genera (such as Allomando) are grown as glasshouse climbers. The shrubby Plumería is the 'Frangipani', grown throughout the tropics for its scented blooms. Some growers of succulents have stretched the limits of their collections to include it on the strength of slightly fleshy branches. Vinca, the periwinkle, is a genus of hardy creepers. The flower parts are in fives but the internal structure is quite complex, approaching that of the Asclepiadaceae (Chapter 19).
Two genera are of interest to all who relish unusual succulents. Adenium has one widespread and variable species, ora few separate species, according to taste, and spans Africa from the southwest through Kenya to Arabia. The habit varies from a low, caudiciform shrub with a massive gnarled trunk to tall erect stem succulents up to 4m (13ft) high. The thick stems are irregularly branched, smooth and unarmed, bearing at their tips flat, leathery, usually slightly shiny, dark green leaves up to 15cm (6in) long in loose spiral rosettes. They drop in the resting season. Adenium in full flower is one of the showiest of all African succulents (18.1). A. obesum is the 'Desert Rose' or 'Mock Azalea' (18.2) and its variety multiflorum is especially suited for small collections because it will bloom from 15cm (6in) rooted cuttings. It is much grownasanornamentalin Malaysia. The flower colour range is from intense red through pink to white with red margins. Adeniums are very tender and thrive in a rich, porous soil, a bright warm situation and water in moderation all the year round.
Pachypodium (18.3-5) is distinguished from Adenium by possessing spines and by its seed, which has a tuft of hair at one end, whereas the seed of Adenium has a tuft at both ends. The 13 species occupy two discrete geographical areas: nine inhabit Madagascar and the other four South and South West Africa and Angola. The South African species include two that are best regarded as caudiciform. In my experience the toughest and easiest to grow is P. lealii ssp. saundersii, which
Adeniums have some of the showiest blooms outside ol Caciaceae. Adenium boehmianum (below, 18 I) is Ihe Impala Lily' ol Soulh West Alrica. Adenium obesum (right, 18.2) is Easl Alrican. All species revel in warmth and will take ample water when in leal.
can be brought from seed to flower in five years. In habitat it is an extraordinary sight, with a massive gnarled trunk up to 1 m (39in) thick at the base and erratically branched like Adenium but more cactuslike. being covered in stout spines in pairs with a third smaller one between them. The deciduous leaves are bright, glossy green and up to 8cm (3in) long. Attractive white flowers appear later in the season — often too late to expand properly in European cultivation. The 10cm (4in) fruits shed large numbers of parachute seeds. P. namaquanum is equally strange and distinctive (18.5): a conical, often unbranched. stem up to 2m (6^ft) tall, with a cabbage-like crown of foliage and spiral rows of tubercles bearing 5cm (2in) spines. In the rugged, moon-like landscape of its natural habitat along the banks of the Orange River one can well imagine being transported to another
Two of the Madagascan species. P. geayi and P. lamerei, come close to P. namaquanum in general facies and have become more readily available during the past decade, even being offered by florists as house plants. With their robust erect stems (usually unbranched in cultivated specimens) and spirally arranged tubercles, each crowned with three long spines, they look extremely cactus-like. But the crown of long narrow leaves at once distinguishes them, and there is no felted areole or spine cushion. P. geayi is the more attractive because of its covering of grey felt on the young growth. An extraordinary cristate cultivar of P. lamerei has been kept going by grafting, and plants with variegated foliage also arise. These two species take plenty of water in the summer and are the most rapid growing.
Other choices are P. densiflorum (18.3) and P. rosulalum with orange to yellow flowers, and P. baronii with red ones. Like the Adeniums, Pachypodium likes warmth at all times, but plants can be brought into the home during winter and thrive on a light, sunny windowsill. When the leaves fall, this is a cue that a dry rest is needed. Both genera graft readily (6.25) but vegetative multiplication is rarely possible and the supply of imported seed hardly meets the demand for such striking and curious novelties.
The Milkweed Family
The Milkweed Family
The milkweed Family —so named after the common American weeds of the type genus Asclepias— is credited with 130 genera and around 2.000 species. They are mostly confined to the tropics and centred in Africa. The Family has been subdivided into six ill-defined Tribes, in all but one of which some form of succulence has evolved. Its closest ally is the Family Apocynaceae, from which it differs in a further floral specialization: the clumping together of pollen grains to form a pollinium. discussed below.
Raphionacme (page 214). Fockea, Brachystelma and some species of Cero-pegia are caudiciform and will be found described in Chapter 21. Cynanchum and Sarcostemma are widely distributed genera of twiners or shrubs with somewhat fleshy rod-like stems, with or without small leaves. The Cynanchum illustrated on page 214 is interesting because of the curious, irregular, warty feel of the stems: the flowers are much more freely produced than in Sarcostemma.
Ceropegia (19.1-4) covers a range of life forms, some quite non-succulent, some stem-succulent, some fleshy leaved and some with long fleshy roots, or clusters of tubers, ora single large caudex. Jacobsen lists 66 species of interest to the grower of succulents. C. dichotoma, C. fusca and their allies form a distinctive little group from the Canary Islands. They bear stiffly erect, jointed, cylindrical succulent stems, and small, narrow leaves that soon drop. The remaining species grow prostrate or twine or are supported by shrubs. Although showy enough when displayed in a glasshouse, many Cero-pegias in nature are inconspicuous, so that hunting them takes on the excitement of pursuing rare orchids. They tend to grow in isolation rather than as dense populations, and seek out the shade of the densest shrubs, so that even when in flower they easily escape detection. Some have been collected on only a few occasions, or are known from only one herbarium specimen. Ceropegia has the leaves opposite or (rarely) in threes, and usually stalked, but sometimes grasslike or reduced to scales. The flowers are tubular, narrow, and 2-12cm (%-5in) long, and their diversity is amazing. At the top of the corolla tube the lobes separate but then usually unite again to form a canopy or umbrella over the top. sometimes with weirdly coloured hairs, spots or outgrowths that attract tiny insects (4.14). Sometimes the apex is drawn out into a spiral several centimetres long. The pollination mechanism is described on page 56.
A few ceropegias have developed highly succulent stems, which in C. stapeliiformis much resemble those of Stapelia although the tubular flower at once distinguishes it. The cristate cultivar defies description (19.1)! But even that is surpassed by C. armandii, a rather delicate rarity from Madagascar, which can best be compared to a lizard moulded from plastic.
A collection of ceropegias is rewarding because no two flowers are alike and their lantern-like appearance never fails to excite
Anthers not so
interest. But it is difficult to accommodate the long trailing stems in a small glasshouse. Some growers buy flower supports or make their own from sticks and wire. The resulting coils of stems look rather more like an electrician's workshop than a floral display, but the flowers make up for lack of charm in the rest of the plant. It is necessary to train the stems frequently, as they grow rapidly and plants may become entangled.
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