#AdventBotany – Getting stuffed at Christmas: Onion

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Of Onions. John Gerard’s Herball, 1597.

Not much of a surprise here, but after covering sage yesterday we really had to say a few words about onions today. If you’re want to be growing your own, then t John Gerard’s herball suggests that ‘The onion requireth a fat ground well digged and dunged.’ However, as they are prone to rots and mildews, it might be better to go with some more modern horticultural advice in this instance! Gerard also reports that ‘it is cherished everie where in kitchen gardens…’ and that certainly hasn’t changed much since the 16th century. It’s fair to say that most of my cooking starts with an onion or two, despite the fact that I only have to look at one for it to make me cry.


Chopping the onion up damages the cells and causes the release of enzymes and compounds resulting in the production of an eye-irritating chemical with the catchy name syn-Propanethial S-oxide (try Scientific American for more detail). If you want to preserve your onion for posterity, it’s the sort of structure which would benefit from being kept as a spirit specimen, but we do have plenty of onion species in the herbarium collections. The Herbarium Handbook (Bridson and Foreman, 1999) recommends slicing bulbs in half before pressing them. Otherwise the bulb will still be alive in the press and may start to sprout. In 1866, the person who prepared this herbarium sheet chose leave the outside layers of the bulb and remove all of the flesh from the inside. This will have made it possible to press it, but I only hope they did this somewhere with good ventilation!

Allium cepa herbarium sheet


The onion has fleshy leaf bases (scales) which surround the budding new plant, and has papery outer layers known as tunics which protect the bulb. A bulb allows a plant to store food reserves so that it can survive a period of dormancy through adverse weather (such as wet, cold winter in the UK, or hot dry Mediterranean summers). This sort of plant is called a geophyte, as the plant’s stores are often underground, where they are better protected from frost, drought or the prying eyes of herbivores. Personally, over the holidays I shall be trying my best to be dormant on the sofa with a good supply of chocolate to see me through the dark and the cold.



Sea squill, sea squill on the sea shore

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by Jemma

Earlier in the month Rachel went on a trip to Mallorca, with a group of 1st year undergraduates from the University of Manchester (for more information see her blog post: https://herbologymanchester.wordpress.com/2015/04/07/surviving-salt-and-waterlogging-on-the-albuferita-mallorca/). During her time there she saw a number of sea squills (Drimia maritima) so I thought I would write a post about this interesting plant.

Sea squill from Albuferita, Mallorca
Sea squill from Boquer Valley, Mallorca

Drimia maritima is a poisonous plant that grows in rocky coastal habitats across southern Europe, western Asia and northern Africa. It grows from a large bulb that can be up to 20 cm wide and a kilogram in weight. In the spring, the bulb produces a rosette of dark green, leathery leaves that can reach up to a metre long. The leaves die away by autumn, when a shoot containing the flowers grows from the bulb. This flower-bearing shoot can achieve a height of up to 2 metres. Pollination of the Drimia maritima flowers occurs by both insects (specifically the western honey bee, the Oriental hornet, and the paper wasp) and wind.

The flowers and bulb of Drimia maritima Image taken from http://en.wikipedia.org/wiki/Drimia_maritima
The flowers and bulb of Drimia maritima
Image taken from http://en.wikipedia.org/wiki/Drimia_maritima
Drimia maritimia flowers Image taken from http://www.xericworld.com/forums/attachment.php?attachmentid=6344&stc=1&thumb=1&d=1341359115
Drimia maritima flowers
Image taken from http://www.xericworld.com/forums/attachment.php?attachmentid=6344&stc=1&thumb=1&d=1341359115

Drimia maritima has been mentioned as far back as the 16th century BCE in the Ebers Papyrus (an ancient Egyptian medicinal text). In the 6th century BCE the Greek philosopher Pythagoras wrote about the uses of squill and, along with Dioscorides (1st century ACE and author of De Materia Medica), recommended hanging the bulb to protect against evil spirits.

Materia Medica jar containing sea squill bulb
Materia Medica jar containing sea squill bulb

One of the earliest medical applications of the sea squill came from the Greek physician Hippocrates (4th century BCE), who advocated its use to treat jaundice (yellowing of the skin), convulsions and asthma. Over the centuries, Drimia maritima was used as a common treatment for dropsy (abnormal accumulation of fluid in tissues) before the more effective foxglove (Digitalis sp.) became the standard treatment during the 18th century.  The plant has also been used in folk medicine as a laxative and to clear mucus build-up.

Materia Medica jar containing sea squill
Materia Medica jar containing sea squill

In addition to its medicinal use, squill has been employed as a poison. All parts of the plant contain toxic chemicals. Once such compound, called Scilliroside, was shown in 1942 to be an effective rodenticide that is avoided by most other animals. In the 20th century, Drimia maritima began to be experimented on to develop highly toxic varieties for use in rat poison. Though not the most common rodenticide, interest in squill’s rat killing abilities has increased dramatically since many rats became resistant to the coumarin-based poisons previously used.