Rose Plants, medicine and fungus

More than 8000 varieties of rose have been developed for garden cultivation - yet all of them are descended from a mere handful of wild species. Roses have been cultivated for almost 5000 years and were known to the Persians, Greeks and Romans, but until the end of the 18th century only four or five species were grown. They included the dog rose, musk rose.

Phoenician rose and the red Provins rose, which became the emblem of the Lancastrians during the 15th-century Wars of the Roses in Britain. The white rose of York was probably a form of dog rose. Modern varieties such as hybrid tea roses (single- flowered) and floribundas (cluster-flowered) began to be bred only around 1900, after the European species were crossed with cultivated oriental species imported from China.

The floating Wolffia species-members of the duck- weed family-are among the world's smallest flower- ing plants. WoIffia arrhiza. which occurs on freshwater ponds and lakes in most continents, is a rootless green blob as little as 0.5mm (0.02in) across.

Many plant species produce drugs which are invaluable in modern medicine. The foxglove is the source of the drug digitalis, which is used to treat heart disease.

But it was used in home medicine long before the medical profession recognised its value and began extracting the drug in the late 18th century. Deadly nightshade. Atropa belIadonna. yields atro- pine, a drug used to dilate the pupils so that an optician, say, can more easily see the retina at the back of the eye. Opium, morphine and heroin, which are powerful painkillers, come from a type of poppy, Papaver somni/erum. And the ergot fungus, Claviceps purpurea, yields lysergic acid, from which many drugs are produced to treat psychiatric disorders.

South Africa's national flower, the protea, can survive a forest fire. Indeed, it cannot survive without one. When the seeds of the sugarbush, Protea repens, for example, have been fertilised, tough bracts close round the flowerhead containing the seeds, creating a protective shell that can last for up to 20 years. The bracts-containing asbestos-like fibres which are fireproof will not open again until they have been scorched by fire, and they begin to open only when the fire has passed. The fluffyseeds, which have been protected by the bracts, then emerge unscathed - and the wind blows them away to ground newly cleared and fertilised by the fire.

More than 175 South African protea species-over half the number in the region - face eventual extinc- tion because of an invasion by South American ants. In order to propagate, these beautiful plants need the services of the indigenous African ant, which collects the seeds, takes them underground and feeds on the elaiosome, a sweet and oily growth carried on the capsule. The ants then leave the seeds underground, effectively planting them.

The Argentine ant-which probably arrived at the turn of the century in forage imported for the British armies fighting in the Anglo-Boer war has, however, been supplanting the local ant at an increasing rate. Argentine ants also have a taste for the elaiosome, but they eat it on the surface of the ground. So fewer and fewer seeds get buried. Moreover, the more aggressive South American ants destroy any of their African relatives they chance to meet, thus compounding the risk to the flowers.

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