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Tuesday, 11 February 2014

Intriguing Plants: The Sensitive Plant

Mimosa pudica flower - Location: Malifa, Samoa
Mimosa pudica is a plant that is no doubt easily recognised by former students of Samoa College and other schools in Samoa as it was (and still is) often a requirement for those on detention or hard labour to weed them as punishment.  Among its common/vernacular names in English are the names Sensitive plant and Sleeping grass due to the way its leaves fold up when it is disturbed.

Mimosa pudica - Location: Malifa, Samoa
Mimosa pudica  is a common plant in Samoa where it is referred to as Vao fefe (which literally translates as “frightened grass” or “grass that is afraid”) and is found throughout the Pacific although it originates from tropical America. Its close relative Mimosa invisa commonly known in English as Giant sensitive plant or vao fefe pālagi in Samoan is probably remembered with even less fondness by those who during the School Clean Up Days following long holidays have had to deal with cutting it and/or gathering it up for disposal, for while Mimosa pudica is a sprawling plant that spreads out flat on the ground and can be relatively easily pulled up (with care) by the root, its giant relative is a real nasty customer that sprawls out in a scrambling manner and can cover large areas up with tangles of long windy stems.
Mimosa invisa - Location: Malifa, Samoa

To make things worse Mimosa invisa has rather nasty little barb-like prickles that come off and become embedded in the skin. Not only that but their long flexible stems can wrap themselves around the limbs of the unwary or careless leaving behind a multitude of these vicious prickles embedded in the skin as well as equally painful and nasty scratches.  From personal experience and observation both types of injuries need to be treated seriously (with attention to removal of all thorns and careful disinfection of the scratches and punctures) as they can easily become infected without proper care especially in tropical climates.
Mimosa invisa - Close up of thorns

Finding and removing Mimosa invisa while they are still seedlings popping up in newly disturbed or recently cleared areas is the best course of action as it saves hours of painful work later if they are allowed to grow and proliferate.

Mimosa pudica on the other hand has bigger thorns which rarely get detached. The main source of injury associated with them is from walking on them barefoot or while trying to pull them up. The trick to pulling them up is to carefully lift the branching stems up to locate the main stem, then carefully wrapping the rest up in a handy piece of cardboard or cloth (we did not get gloves to do this), then firmly grasping the whole you pull up the tap root.
For those on detention or hard labour if they had a certain number to pull up some enterprising types apparently then carefully splitting the plant up so that each separate part branching off from the central stem had a sliver of the tap root to pass off as separate plants. Of course with a vigilant prefect standing guard that was not always possible. In any case most of us just got told to weed an area and it did not matter how many of these were pulled up.
Mimosa pudica -  Close up of thorns

Both plants belong to the Genus Mimosa which is part of the Plant Family: Fabaceae (also known as the Legume, Bean or Pea Family).

Nitrogen fixing
Like other members of Fabaceae it can form root nodules that are inhabited by nitrogen fixing bacteria. Various members of Fabaceae have long been used in agriculture as green manure. However, I do not foresee anyone growing Mimosa pudica for its nitrogen fixing properties given how many other less problematic or prickly relatives it has that can be used for that purpose. On the other hand perhaps there may be a future for growing it for its other properties.
Although some sources indicate that Mimosa invisa has been used as fodder for cattle the very thought of cattle eating those vicious looking stems coated as they are with thorns is an unpleasant image at the least.

The interesting thing about Mimosa pudica aside from the bizarre fact (to those who have had to weed it as punishment or to get it out of their own lawns, gardens or crops) that in some countries it is actually grown and sold as a curiosity (for the way its leaves fold up when disturbed) is that scientific research has discovered that its roots contain a plant amino acid, mimosine which causes cell apoptosis or cell death. That is it mimosine triggers the mechanism in cells that causes the cell to stop growing and proliferating and leads to it dying. Hence “cell death”

Apoptotic and antiproliferative and effects of Miosine
Now the really interesting and promising thing about the discovery of such naturally occurring molecules is the implication for cancer research and the treatment of cancer, in particular a less invasive, less toxic and less gruelling treatment than currently available using surgery and chemotherapy.
The discovery came about through the linking of several prior studies which led to the question as to possible application in cancer treatment. Basically the two core bits of information drawn from earlier studies upon which the study based its hypothesis were:
Firstly the knowledge that iron played a vital role in cell proliferation (which is the core problem with cancer tumours, i.e. uncontrolled growth of the tumour as well as metastasis or spreading of these cancerous cells to other areas of the body). A horticultural analogy of metastasis it would a fungus growing and then sending out spores which is pretty much what happens when cancerous cells from a tumour spread through the body through the blood stream after penetrating the walls of lymphatic and/or blood vessels.
Apparently earlier scientific studies on Mimosa pudica had shown that mimosine had a anti-proliferative and apoptotic effects in certain cultured cells by blocking the absorption of iron.

For those interested here is the link and reference to the study

What medical scientists are looking into is the possibility of extracting or perhaps synthesising mimosine which could then be introduced into the cancer cells of patients to trigger the death of the cancer cells. It would be like sending James Bond to infiltrate the top secret base of some arch villain to push the self destruct button on the villain’s latest weapon of mass destruction and world domination.
Other scientific studies on Mimosa pudica showed that aqueous ethanol extracts of its leaves had antiproliferative and apoptotic effects.

Immobilising effect on stercoralis filariform larvae
A Jamaican scientific study which looked at the effects of plant extracts found that aqueous ethanol extracts from Mimosa pudica leaves immobilised the stercoralis filariform larvae. Five other plant extracts were tested as well as three commercially available drugs; albendazole, thiabendazole and levamisole. In the study, the extract from green leaves of Mimosa pudica and the drug levamisole were the quickest to affect the larvae, immobilising them in under one hour.
For those interested here is the link and reference to study
Strongyloides stercoralis is a small ground dwelling nematode (roundworm) that can cause a chronic infection called Strongyloidiasis in baboons and chimpanzees as well as humans when they become infected by this intestinal parasite.
Note: Apparently in the US it is known as threadworm while in the UK it is referred to as pinworm since in the UK the term threadworm refers to nematodes of another genus. (I have not been able to discern what it is called in other English speaking countries but would suspect that Commonwealth states would most likely use the United Kingdom term).
Apparently the life cycle of Strongyloides stercoralis is both complex and unique among intestinal nematodes because it alternates between free-living and parasitic cycles as well as its ability for autoinfection and multiplying within the host which not only increases its success as an organism but poses certain challenges in treating those infected. This is because current treatment only affects certain forms of the parasite at certain stages of its life cycle. Since it is able to auto infects host and reproduce in the host this means that the treatment is lengthy in order to eradicate the parasite completely.
The discovery that mimosine is able to immobilise the stercoralis filariform larvae may therefore have practical applications although it is not clear as to its effectiveness against other forms of the parasite.
Another issue regarding the potential for its use in treating this parasitic disease is that the existing drugs can have negative side effects which the mimosine extract might not have. (NB. No human studies appear to have been done yet).

To be continued in Part 2:
Other scientific studies on potential medical use of Mimosa 

Use of Mimosa pudica in Traditional  Medicine
Modern Medical use and scientific studeis
Other uses of Mimosa pudica

Scientific / Binomial Name: Mimosa pudica
Vernacular / Common names:
English: Sensitive Plant, sleeping grass, humble plant, touch-me-not, shameful plant, ant-plant
Samoan: vao fefe, Tongan: mateloi, Tahitian:  pohe ha’avare, Fijian: co gadrogadro
Portuguese: não-me-toque (touch-me-not), sensitiva (sensitive) or dormideira (roughly "sleeper")
 Spanish: morí-viví or moriviví
Indonesian: putri-malu
Belongs to the Fafaceae Family, (Pea Family)
Binomial Name: Mimosa invisa
Common names: Giant Sensitive Plant, sleeping grass, vao fefe palagi (Samoa)

  • Family: Fabaceae – Genus: Mimosa – Species: Mimosa púdica
  • Family: Fabaceae – Genus: Mimosa – Species: Mimosa invisa
  • Family:– Genus: Strongyloides  – Species: Strongyloides stercoralis
  • Family:– Genus:Naja  – Species: Naja kaouthia
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References books
Whistler, W. Arthur, “Wayside Plants of the Islands. A Guide to the Lowland Flora of the Pacific Islands including Hawai’i Samoa Tonga Tahiti Fiji Guam Belau”, Isle Botanica, Honolulu, 1995.
ISBN 0-9645426-0-9
Reference online sources:
Kew Royal Botanical Gardens Entry for Mimosa pudica
Robinson RD, Williams LA, Lindo JF, Terry SI, Mansingh A (1990). "Inactivation of strongyloides stercoralis filariform larvae in vitro by six Jamaican plant extracts and three commercial anthelmintics". West Indian Medical Journal 39 (4): 213–217. PMID 2082565.
Wikipedia Entry for Mimosa pudica
Wikipedia Entry for Necrosis
Wikipedia Entry for Strongyloides strecoralis


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