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Ornamental Adenium Tree

The Adenium genus is made up of tiny evergreen tree from the dogbane family.  The succulent trees come from Africa where they can be found in the Sahel (the semi-arid strip running along the south of the Sahara) and similar dry scrublands down the continent to South Africa.  The most famous species is Adenium obesum, a little shrub which grows from 1 to 3 meters (3 to 9 feet) in height and bears dazzling five petaled flowers that look like glowing stars of pink, red, and white. The flowers are widely cultivated as houseplants known as the desert rose (although they are in no way closely related to true roses).  A whole group of enthusiasts hold contests to determine who can hybridize the prettiest flower or cultivate the most striking ornamental bonsai trees.

In addition to their dazzling flowers, Adenium plants are known for having bulbous interestingly-shaped caudexes.  A caudex is the woody barrel-like stem/trunk in which certain desert trees and shrubs store precious liquids. Adeniums are very lovely but their loveliness should not obscure the fact that the wild specimens survive in one of the more punishingly competitive ecosystems on Earth–where all sorts of hungry grazers are desperately looking for meals.  To survive in Africa’s scrublands, Adeniums are not only hardy plants which can live almost anywhere on very little water, they are also poisonous.  Adeniums produce a cocktail of cardiac glycosides-compounds which affect the electrophysiology of the heart. Although these molecules (and other related cardiac glycosides such as those found in the foxglove) can be therapeutic in very tiny doses for certain heart conditions, in larger doses they are poisonous and cause the heart’s rhythm to fail altogether.  Thus, a plant known to American housewives as an frou-frou ornamental houseplant is known as the source of horrifying arrow poison to many of Africa’s toughest native hunters, who use the compound to kill big game.

San hunters of the Kalahari

A Close-up photo of a Foxglove from "Ledge and Gardens"

The garden at my new residence contains a variety of beautiful old trees (like the cherry tree which I wrote about this spring).  While the trees are delightful and are clearly the best features of the garden, they do make flower gardening a challenge.  Fortunately there is a very beautiful plant that thrives in the dappled shade—the foxglove.  I just planted two mature specimens which I obtained from the nursery and I am delighted with them!  I thought I should feature a picture of them here before their flower spikes get broken.

Foxgloves in my Brooklyn Garden

Because they are so tall and elegant, foxgloves have been a garden mainstay for an extremely long time.  About twenty species of wild foxgloves (the genus in named “digitalis”) are indigenous to Europe, North Africa, and Western Asia.  The plants are biennials and they produce foliage in a low basal clump.  During the plant’s second year, a tall rosette rises from the leaves and produces a series of purple, white, or pink tube-shaped flowers.  The throats of these flowers are mottled with lovely speckles.

A Second Photo from the Garden

Foxgloves have long been associated with magic and myth.  In Roman mythology, the goddess Juno was angered that Jupiter had given birth to Minerva without a mother.  Juno aired this grievance to Flora, the goddess of flowers, who then lightly touched the queen of gods on her breasts and belly with a foxglove.  Juno was impregnated and gave birth to the war god Mars, who, in the Roman canon has no father (like certain turkeys!). The Scandinavians call the plant “fox bells” a name which references an ancient fairy tale about how foxes magically ring the flowers when hunters are coming (so as to warn their kind of peril).  On her botanical folklore website, Allison Cox wrote “In Wales, foxglove was called Goblin’s Gloves and was said to attract the hobgoblins who wore the long bells on their fingers as gloves that imparted magical properties.”

A Patch of Foxgloves

Unfortunately, the plant has a very real dark side. All parts of the foxglove are toxic.  Mammals that have ingested digitalis suffer tremors and nerve disorders (particularly xanthopsia, a visual impairment in which the world becomes suffused with yellow and haloes appear around lights).  Even a small amount of the poison is enough to cause deadly disturbances of the heart.

Because of its ability to affect the heart, digitalis was one of the very first cardiac medicines. The biochemistry website “Molecule of the Month” relates that, “Digitalis is an example of a cardio-active or cardiotonic drug, in other words a steroid which has the ability to exert a specific and powerful action on the cardiac muscle in animals, and has been used in the treatment of heart conditions ever since its discovery in 1775.”  The site has a very entertaining anecdote about how William Withering, the proper English doctor who made this discovery was forced to prowl the forgotten byways of Shropshire and bargain with a gypsy sorceress to find out which compound had healed a patient with a fatal heart problem.

Because foxglove was actually useful for certain heart problems, it was also prescribed (or self-administered) to people suffering from palsies and nervous disorders. There were very few effective neurological drugs available at the time and it was believed that digitalis might somehow help (an unfortunate fallacy). Legend relates that Van Gogh used foxglove to treat his epilepsy.  If true it might explain the yellow hue of his late paintings. Digitalis poisoning is known to cause xanthopsia, but whether Van Gogh was truly inspired by the poison flower or just loved yellow will probably forever remain unknown.

Le Café de Nuit (Vincent van Gogh, 1888, oil on canvas)

 

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