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Wednesday, October 16, 2013

Decaisnea fargesii, Dead Man's Fingers, Lardizabalaceae

Mention the word 'autumn' and what colours spring to mind?  Most likely crimson, scarlet, orange, yellow, russet, gold ......... but probably not blue. But that's the colour of the eye-catching fruits of Decaisnea fargesii, ripening in Durham University Botanic Garden today.

This large shrub has attractive, long, pinnate leaves ........

...... grey-green below .....

....... and darker green above, but it's those fruits that make it special. It's hardy so I'm surprised it's not more widely planted. The colour of the pods is most vivid on sunny days, so must be partly due to the reflective properties of the pod surface, in addition to the underlying pigmentation. 

The seeds are surrounded by a jelly-like pulp that's said to be edible but insipid.

Decaisnea fargesii comes from western China 

Saturday, October 5, 2013

Colchicum autumnale, Meadow Saffron or Autumn Crocus, Colchicaceae

Meadow saffron, sometimes known as autumn crocus, also has the rather salacious name of 'naked ladies' which supposedly stems from its lack of leaves when the flowers appear in autumn; the leaves sprout in spring and wither away in summer. The lilac flowers are very attractive to bees.

 This is a rare British native wild plant and most specimens that turn up – like those above, beside a road in Weardale – are garden escapes. To my mind they perform best when grown in grass like those in the photograph; when they’re cultivated in bare soil the floral tubes often grow very long and the flowers fall over in the autumn wind and rain, but some surrounding grass gives them support.

The plant has a long history of cultivation and in 1776 the botanist and doctor William Withering, writing in his Botanical Arrangement of all the Vegetables Growing in Great Britain mentioned that ‘cultivation produces a great variety of colours and makes the blossoms double’.

 In the wild meadow saffron was ruthlessly eliminated because it’s extremely poisonous to grazing livestock, thanks to the presence of toxic colchicine in all parts of the plant. Like many plant poisons colchicine has been used medicinally, in very low doses, to treat gout. Benjamin Franklin, himself a gout sufferer, is supposed to have introduced the plant to the United States for that very purpose. There have been accidental fatalities with poisoning from either eating the plant (its leaves resemble very lush wild garlic) or using it as herbal medicine at lethal concentrations, so one wonders how many of those who followed William Withering’s advice survived, when he wrote ‘This is one of those plants that upon the concurrent testimony of ages was condemned as poisonous; but Dr. Storck of Vienna hath taught us that it is a useful medicine. The roots have a good deal of acrimony. An infusion of them in vinegar, formed into a syrop by the addition of sugar or honey, is found to be a very useful pectoral and diuretic. It seems in its virtues very much to resemble squill, but it is less nauseous and less acrimonious’.

Colchicine is used by plant breeders to double the number of chromosomes in plants, because the drug allows the chromosomes to divide without the cell they are in dividing, so doubling the number of chromosomes in the cell - a phenomenon known as polyploidy. More chromosomes per cell tend to produce larger cells and larger cells lead to larger plants and better crops.

All sorts of unnaturally large plants, ranging from strawberries to hyacinths, have been bred using this long-standing form of genetic manipulation, which has been in use for over a century. Crossing a colchicine-induced tetraploid, which has double the normal chromosone complement, with a diploid plant that has the normal complement of chromosomes produces plants called triploids, with three sets of chromosomes per cell, which are seed- sterile – a common breeding technique for producing seedless fruit such as bananas.