Like the Compositae, the Euphorbieae have evolved an inflorescence that looks and functions like a single flower. Let us take a close look at one of the most familiar: the 'Crown of Thorns', Euphorbia milii (splendens) (20.6). The two red organs are not petals but coloured bracts, and each bears in its axil a dormant bud that can later grow out and add a new branch to the inflorescence. In the centre we find a single female flower reduced to

| THE SPURGE FAMILY (EUPHORBIACEAE) —A breakdown to genus level (succulent members)

(Inflorescence a dichasial thyrse; flowers separate, not enveloped by a >n involucre

into cyathia. The end product is unquestionably successful, having the same advantages as the capitulum of Compo-sitae. and contributes to the wide distribution and protean diversity of the genus Euphorbia.

Only Senecio rivals Euphorbia in the variety of shapes and oddly diverse forms it offers, so both are ideal subjects for a collector wishing to specialize. The genus is estimated to include 2.000 species, distributed all over the world and ranging from tiny annual weeds through herbs, shrubs and trees of the tropics. Among the non-succulent species valued in gardensare many hardy foliage plants for the border, such as £ characias and E. cyparissias. and for the indoor window-sills £ pulcherrima, "Poinsettia'. with large red bracts. But it is in central and southern Africa that the genus comes into its own, with xerophytes of all sorts and cactus-mimics of all sizes: 463 species, according to Jacobsen (1975). A few are

Right (20.3): The curious cyathia ot Euphorbia globosa: what seem to be "petals" are the much enlarged, while encrusted, three-lobed glands ot the involucre.

caudiciform. the rest stem-succulent; leaf succulence, oddly enough, is restricted to one or two dwarf species, such as £. cylindrifolia and £ decaryU20.7). Otherwise the leaves are flat, entire, more or less deciduous, and often reduced to grass-like blades or tiny scales.

Throughout all this diversity of habit, the cyathia remain constant to the plan described above, although varying greatly in the colour, shape and form of the involucral bracts. Some compare Euphorbia unfavourably to the cacti because of its smaller flowers, but collectively these can put up quite a display.

Left (20.5]: The "flower" of a spurge is actually a whole inflorescence (cyalhium) made up of a single central female I lower [floret] reduced to three styles and a ihree-lobed ovary, surrounded by several male florets, each reduced to a single stamen. The whole is surrounded by bracts and bracteoles forming an involucre

Below (20 6) Euphorbia milii, the popular Crown of Thorns'from Madagascar, makes a good house plant and is rarely without flowers. A variety with yellow bracts is less popular

armed, but others have arms of the most diverse origins, and it is convenient to group the species according to whether they possess prickles, thorns or spines. So many are favoured by collectors that it is impossible to escape the charge of bias in choosing just a few here.

Beginning with unarmed species, E. bubalina is a good beginner's plant: quick-growing, with a thick upright green stem covered with low tubercles and lance-shaped leaves up to 10cm (4in) long in a terminal lax rosette. It eventually forms a small shrub, and is self-compatible.

and last a good deal longer than cactus blooms. Some species are dioecious, and the grower who wants seed will need two plants, onea maleand the othera female.

A long history. The latex of Euphorbia is carried in special branching latex tubes that circulate throughout the plant. Although they undoubtedly defend it against grazing animals, they have been blamed for the quick spread of disease and death of the plant once bacterial or fungal spores effect an entrance. This latex is responsible for taking Euphorbia history back 2,500 years to the dawn of medicine, when Hippocrates, the father of medicine, is supposed to have known its properties. The popular name "spurge" comes from the same root as purge and expurgate, alluding to its properties if taken internally. Credit for discovering the first succulent Euphorbia on Mount Atlas (probably £ resinifera, 20.9) goes to King Juba II of Mauretania in the first centuiy BC. He named it Euphorbia after his physician Euphorbus.

Euphorbia. Some euphorbias are un seeding itself if given the chance. Another long-lived, trouble-free species is £ globosa, with chains of walnut-shaped joints and long slender inflorescences with curious hand-like outgrowths from the involucres (20.3). In both these the dried inflorescence stalks persist and point to the way that thorns developed.

The 'Medusa Head' euphorbias get their name from the first discovered. £ caput-medusae from the Cape district of South Africa (5.6): a stout club-shaped trunk bears a head of thick, tortuous, snake-like branches. £ woodii (flanaganii)

is a smaller version very popular in collections (20.8) and it exists in two cristate cultivars, one with the main trunk fasciated and normal branches, the other grown from a cristate side branch, with no trunk.

£ bupleurifolia, obesa (symmetrica) and suzannae are much-esteemed dwarf globose dioecious species of which the first two never branch unless damaged, so seed is the only mode of propagation. £ bupleurifolia and suzannae are covered in tubercles, but £ obesa (20.10) is smooth and reddish brown with faint

Lelt (20.9) Euphorbia resinifera shrubs that owe nothing their compact, neatly trirr.

striping, with eight low ribs, and fancifully compared to a football.

Turning to plants with surface prickles, we have a large group of bramble-like shrubs from Madagascar centred around £ milii (splendens). already referred to. Whereas the large paired prickles could very well be modified stipules, others arise direct from the stem surface, as in the blackberry (Rubus). £ milii(20.6) is a deservedly popular house plant, thoroughly at home in the hot dry atmosphere of centrally heated rooms, where it is in flower almost throughout the year. Its one disadvantage is its dropping of withered leaves.

Thorns in the euphorbias (2.13) can be recognized as the old. withered inflorescences in £ meloformis (valida). where the remains of cyathia can still be seen. This is another dioecious species, long beloved of collectors and much like an Echinocactus at first glance. In £ ferox, £ pentagona and £ mammillaris the thorns are needle-like and bear only the tiniest, just discernible scales as evidence of their branch origin. Very curious thorn developments occur in £ columnaris (20.12), a rarity from northern Somalia, where each is divided into two, and in £ stellispina. where each thom has four or more points arranged like a star.

A great many euphorbias have spines developed in pairs at the leaf base from modified stipules (20.2). Among these are tall trees such as £ ingens. a conspic-

Lelt (20.9) Euphorbia resinifera shrubs that owe nothing their compact, neatly trirr.

Below (20.10): Euphorbia obesa has the ultimate in surface reduction to a sphere, w attractive markings suggesting a

Below (20.10): Euphorbia obesa has the ultimate in surface reduction to a sphere, w attractive markings suggesting a

uousand unique feature of areas of South Africa, and medium to large shrubs such as £ avasmontana and £ memoralis. Where euphorbias can be bedded or grown permanently in the open, some of these arborescent species are essential: their appearance is unique, and there are many from which to choose. £ candelabrum var. erythraea is a favourite for its four-angled cereoid stems with slightly wavy margins. Specimens in large pots can be used to decorate annexes in office buildings that have plate glass windows facing the sun. But in a small glasshouse they take up too much room, and attention turns naturally to the smaller types, of which there are many. Special praise goes to £. aeruginosa for its dramatic patterning of stems, and to £ tortirama for the quaintly spiralled ribs. £ grandi-cornis excels in fierce spines, up to 10cm (4in) long, but it is a large grower and rather tender.

Madagascan species in which the stipules are elaborated into fringes or crests running down the stems like ribs. Examples are £ leuconeura (20.14) and £ neohumberlii. Beautiful miniatures with a bonsai look are £ francoisiiand £. decaryi (20.7). The demand exceeds the supply for these choice species, which are more suited to the experienced grower than to the beginner.

Other genera. Synadenium is a genus of two East African species of shrubs with cylindrical fleshy branches and large, thin, deciduous leaves. It makes a good house plant, but the sap is poisonous.

Pedilanllius also has cylindrical, unarmed. fleshy stems, usually grey and much branched, with tiny deciduous leaves. It is native to the warmer parts of America and has six species. The popular name is "slipper flower", referring to the shoe-like form of the highly zygomorphic cyathium, a feature also shown in the Old World genus Monadenium (20.11). This runs parallel to Euphorbia in many ways, and includes caudiciform species mentioned in Chapter 21. Coming from tropical and East Africa it requires considerable warmth and is rarely met with outside specialist collections. Nevertheless. the species include some real treasures, and some with notably showy flower heads (21.16).

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook

Post a comment