Plants Fight Back

David Beeson, 31^st May 2021

If someone attempts to steal your money would you be happy? Here you are, have another £1000. I doubt it. So, plants will feel the same about being eaten … the organism is taking the plant’s resources and giving nothing in exchange.

Okay, what do you do to stop the thieves and scammers? I use an alarm system, security windows and a big lock on the door. I even remember to use the lock occasionally! Scammers … I always say ‘No’, and am wary. Plants use poisons, toxins. Virtually every plant, except quick-growing annuals and grasses, are protected at maturity with toxins. (Grasses contain silicates that wear down herbivores’ teeth and limit their consumption.)

Toxicity Class

1. Major Toxicity: These plants may cause serious illness or death.
2. Minor Toxicity: Ingestion of these plants may cause minor illnesses such as vomiting or diarrhoea.
3. Oxalates: The juice or sap of these plants contains oxalate crystals. These needle-shaped crystals can irritate the skin, mouth, tongue, and throat, resulting in throat swelling, breathing difficulties, burning pain, and stomach upset.
4. Dermatitis: The juice, sap, or thorns of these plants may cause a skin rash or irritation. Wash the affected area of skin with soap and water as soon as possible after contact. The rashes may be very serious and painful.

Some examples:

Acer spp.             Maple   4

Achillea millefolium         Yarrow   2,4

Aconitum spp.   Aconite; Monkshood      1

Aesculus spp.     Horse chestnut  2

Agapanthus spp.              Agapanthus       2,4

lcea rosea            Hollyhock            4

Allium spp.          Wild onion          2

Alnus spp.           Alder     4

Aquilegia spp.    Columbine          2

Aster spp.            Aster     4

Atropa belladonna          Deadly nightshade          1

Aucuba japonica              Japanese aucuba (A common hedging plant)            2

Begonia spp. (some species)        Begonia               2,3

Bellis perennis   English daisy      4 (Our rabbit ate the ‘flower’ stem but did not touch the flower head.)

Berberis spp.      Barberry              2,4

Betula spp.         Birch tree             2,4 (Luckily the syrup, like maple syrup, is fine and delicious!)

Lots more on: https://ucanr.edu/sites/poisonous_safe_plants/Toxic_Plants_by_Scientific_Name_685/

Generally, the toxicity builds up with time. Growing new leaves is an energy intensive process, so the plant delays the energy-expensive toxin production until the leaves are established. This gives the leaf-eating insects a chance to feed – a rush before they are inhibited by the increasing toxicity of their food. This why birds such as tits, feeding on tree-dwelling larvae, must complete their breeding cycle before the maturity of tree leaves.

Heracleum sphondylium – Common hogweed.

The name of this tall wayside wildflower comes from its farming history, as it was once frequently collected and bundled by villagers in the summer months and used as pig-fodder

Keeping with this theme, it is also said that when in flower this plant gives off a less than pleasant, rather pig-like odour!

As a gardener, I come across plant toxicity on my skin. In the past ( I Poison Myself article) with euphorbia sap and today with the leaves of Common Hogweed … I was wearing gloves, but the leaves still touched my uncovered arm which had a mild rash. (Water washing has calmed it down.) (Hogweed is edible: young leaves are blanched, and then cooked in butter – giving a spinach-like end product.)

The snag for me is that common hogweed spreads too well in my garden. If I did not spend some time controlling it the garden would be covered in nothing else. So, I remove the flowering shoots of the biennial, and this keeps it at a low population level.

In eastern European countries and especially Romania, H. sphondylium is used as an aphrodisiac and to treat gynecological and fertility problems and impotence. It is also sometimes recommended for epilepsy. However, there are no clinical studies to prove its efficacy at treating any of these problems.

It seems that my allergic reaction was uncommon, but it was a high light intensity day (a rare thing this year!) and the skin irritant was enhanced by UV light.

Hogweed toxins can induce phytophotodermatitis –  irritating the skin of susceptible people and causing blisters with exposure to ultraviolet radiation. The furanocoumarins are changed temporarily into a high-energy state when they absorb photons from the sunlight. They then release this energy into the skin where it causes damage to DNA in the skin’s epidermis, causing skin cell death.

You and I will have many toxic plants in the garden, and gloves should be worn when one is doing lots of weeding or plant manipulation. I have Deadly Nightshade in a hedge, and Monk’s Hood in the flower borders – two very toxic plants in category 1. I have just planted out some Ammi majus for its insect-attracting white flowers, and this, I now note, is highly toxic. Guess it is more glove use for me in the future.

Sundews. On my New Forest trip last week, I came across two species of sundews – really interesting carnivorous plants growing in a mossy bog. Nearby was the semi-parasitic lousewort. These are plants fighting back too.

Now, just for fun … can anyone recognise this place?

http://www.nwhwildlife.org is the homepage. This gives access to 100 ad-free articles.

Feedback: dandabeeson@gmail.com

The seaside? Oceanside, California. Yup, that was hard!