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Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
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Mimosa pudica - Sensitive Plant - Is it benefiting the area it is
growing in?
Chloe Williams
Madagascar Terrestrial Research Programme
Phase 134
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Introduction
In Madagascar in September 2013, I undertook a project on Mimosa pudica, also known as the
Sensitive Plant. I carried out a number of tests to investigate its impact on the environment and
ecosystem it inhabits. Native Madagascans use it to treat allergies and stress. (Bordieu et al.,
2013). The plant is found all over the world, but there are limited studies on whether they are
harmful to the ecosystems they inhabit. The study was conducted on the island of Nosy Be,
located off the North West coast of Madagascar
Figure 1: Map of Madagascar
with Location of Nosy Be
The capital of Nosy Be is Hell-Ville, also known as Andoany. Nosy Be is heavily populated, with an
estimated population of 60,000. Combined with an ever growing tourism industry, there has been a
major impact on the environment and ecosystem on the Island (Journeys International website,
2013)
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Mimosa pudica is a creeping annual or perennial herb native to South and Central America, which
grows in a creeping manner. It is now a Pan-tropical invasive weed with an increasing distribution
worldwide (Kew Botanical Gardens website, 2013). The compound leaves fold inward and droop
when touched or shaken to protect them from predators and re-open minutes later (Kew Botanic
Garden Website, 2013). The Sensitive Plant has a tap root system, a large main root from which
smaller roots grow (Encyclopaedia Britannica website, 2013).
The study looked at the following:
- Is this plant a major tropical weed in Madagascar?
- Is it benefiting the area it is growing in?
- Would it affect the ecosystem if it disappeared?
The Mimosa pudica specimen studied was at a Frontier survey site known as 5.5, an area of
secondary forest that is bordered a rice paddy field.
The Sensitive Plant is located next to a frequently used path way, coordinates
S13’24.285’E048’20.716’ (Figure 2)
Figure 2: Mimosa pudica
This plant is 3 m wide, 5 m long and 1 m high. It is growing in heavy loamy clay soil, with a small
amount of sand and organic matter on top of the soil. The soil has a pH of 6, indicating it was
slightly acidic. It flowered every morning with an average of 5-12 blooms, which closed around late
afternoon. The flower has no petals and is best described as pedunculate (World Plants website,
2013) (Figure 3).
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Figure 3: The Mimosa pudica flower
The leaves are compound, and the top of the leaves are much darker green then the underneath
(Figure 4).
Figure 4: Mimosa pudica leaves
These leaves react to many stimuli by ‘closing up’ (the leaves folding inwards), only to re-open
minutes later (Plant Scientist website, 2013). Several tests were performed during this study to
discover these stimuli.
The seed pods are 2-3 cm long with stiff bristles along the edges (Figure 5). The pods eventually
break up into spate seeds that are only 3 mm diameter. The seed is spread by clinging onto humans
and animals. The seed can be viable for years (Kew Botanical Gardens website, 2013).
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Figure 5: Mimosa pudica seed head
Methodology
Experiment 1: How long does it take for the ‘closed up’ leaves on the Mimosa pudica to re-open
after being touched?
This tested how long the leaves took to re-open after being stimulated to close by touch. I touched the
leaves once during the following times and a stopwatch was used to record how long the leaf took to
reopen:
-
In the morning while the plant was in shade
When the plant was in full sun
In the afternoon when the plant was in full sun
When the plant was in shade
The test was repeated daily from the 8/9/2013-23/9/2013.
Experiment 2: What would make the Mimosa pudica leaf react and close up?
The plant was stimulated using the following methods and they were repeated three times on
separate days for each method. Tests were undertaken either in the morning or afternoon.
1. Touch (morning)
a. A leaf was stroked along its full length with an index finger
b. Three leaves were randomly chosen on different parts of the plant each morning.
2. Flame
a. A flame from a lighter was put under a leaf for 2 seconds.
b. Three leaves were randomly chosen on different parts of the plant each morning.
3. Smoke (using a cigarette)
a. After lighting a cigarette, it was moved slowly under a leaf for 2 seconds
b. Three leaves were randomly chosen on different parts of the plant each morning.
4. Water – Salt and Fresh
a. Using a teat pipette, drops were administered over the top of one leaf for 2
seconds.
b. Three leaves were randomly chosen on different parts of the plant each morning.
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
5. Wind (a human blowing on the leaves)
a. Using my own breath I blew onto the top of the leaf for 2 seconds.
b. Three leaves were randomly chosen from different parts of the plant each morning.
6. Dust/Soil/Sand on the leaves
a. Soil, sand or dust was sprinkled over the top of the leaves using my hands, for 2
seconds. Using a water bottle cap filled to the top with the soil or sand dust.
b. Three leaves were randomly chosen from different parts of the plant each
morning.
Experiment 3: Observations
The Mimosa pudica was observed at several times of day (for a total of 50 hours) for the following:
-
What wildlife lived on the plant?
What wildlife used the plant for shelter and/or food?
General activity in the immediate vicinity of the plant.
What is the average total of leaves on the Mimosa pudica?
How long does it take the Mimosa pudica flower to develop into a seed pod?
Equipment
The equipment I needed to complete this study is detailed below:
Experiment 1:
-
Pen
Paper
Stop watch
Camera
Experiment 2:
-
Pen
Paper
Camera
Salt water
Fresh water
Sand
- Soil
- Lighter
- Cigarette
Experiment 3:
- Pen
- Paper
- Camera
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Results
Experiment 1: How long does it take for the ‘closed up’ leaf on the Mimosa pudica to re-open
after
being touched (in minutes)?
Reading
Shade – AM
Shade - PM
Full Sun - AM
Full Sun – PM
1
30
*
24
10
2
11
*
8
8
3
9
27
14
10
4
36
26
*
10
5
*
*
*
14
6
*
*
*
12
7
*
*
*
7
TOTAL AVERAGE
21.5
26.5
15.3
10.1
(minutes)
*unable to record time as the plant was not fully under the condition needed, e.g. full sun.
Experiment 2: What would make the Mimosa pudica leaf react and close up?
Stimulus
Reaction
Touch
Flame
Smoke (using a cigarette)
Water – Salt
Water – Fresh
Wind (blowing on the leaves)
Dust / Soil on the leaves
Yes
Yes
No
Yes
Yes
Yes
Yes
Strength of reaction (ranked from
1 (strongest) to 7 (weakest))
2
1
NA - no reaction
3
6
4
5
Experiment 3: Observations

There were several species of insects observed pollinating the flowers, such as bees, ants
and butterflies. When the flowers were observed closely on other Mimosa pudica
specimens on Nosy Be, their colour was observed to be ranging from pink to purple,
depending on the age of the plant, the type soil it was growing in (sandy or clay) and its
pH.

The Mimosa pudica took about a week for the flower’s to turn to seed, if they had been
pollinated. An average total of 46 leaves, 23 on each side were counted on the specimen
(Figure 4).

The leaves did not react on a windy day to the wind.
Of all the insects noted on this plant, the Caterpillar (Figure 6) was frequently seen to eat this plant,
especially the new growth. 3 different types of Caterpillar were observed and they were most active
during early morning and late afternoon.
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Figure 6: A caterpillar on the Mimosa pudica
Another insect that I observed eating the new growth was the Cricket. I saw two different types of
crickets. I observed a cricket being preyed upon by Trachylepis gravenhorsti, the Madagascar skink.
I observed ants going to fresh flower buds and biting the part joining them to the branch and
holding onto it. I also observed a number of bees, beetles, spiders and butterflies.
Dragonflies and Damselflies would land on the leaves and rest for a few minutes. (Figure 7)
Figure 7: A Damselflies on the Mimosa pudica plant
Two Dromicodryas quadrilineatus snakes were seen on one occasion. Neither snake rested beneath
the plant. A number of birds were seen eating the various insects on the plant.
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Discussion
Minutes
Figure 8: Minutes taken for the 'closed up' leaf on the
Mimosa pudica to re-open after being touched
40
35
30
25
20
15
10
5
0
Shade AM
Shade PM
Full-Sun AM
Full-Sun PM
1
2
3
4
Test
5
6
7
There is great variation in leaf reaction / closing times throughout the day (Figure 8). A possible
explanation for this is that the amount of direct sunlight has an effect on the level of solar energy the
plant has available to utilise. This theory of energy levels could be supported by the fact that the more
the plant becomes habituated, the longer the closure times, as the plants energy supply becomes
depleted. How the plant uses its energy depends on the development stage of the plant and
environmental conditions (West Virginia University website, 2013).
When stimulated by touch, all the leaves would close up, but it only affected the group of leaves that
had just been touched. The strongest reaction to a stimulus was when a flame was put under the
leaves; all the leaves at the front of the plant started to close up, followed by the second row, third
row and so on; until all the leaves closed up on the branch the flame was under. When just smoke
was put under the leaves using the cigarette, there was no reaction at all. This is an interesting
reaction and the results suggest the plant may only respond to the heat of an actual fire and not the
smoke.
Both salt water straight from the sea and fresh water elicited a reaction. The response to salt water
was a lot faster than the fresh water, and all the leaves closed up with salt water. This suggests it is
the salt in the water that has the greater effect. This could be because once inside the cells of the
leaf, salt can cause ionic stresses, largely as sodium (and chloride) inhibits metabolic processes
including protein synthesis. Sodium can rise to toxic levels in older leaves, causing them to die, so
the reaction to water could be a defense mechanism (University of Cambridge website, 2013).
On a windy day, the leaves showed no reaction to the wind itself; however when the leaves were
blown on by a human they responded. One theory for this could be over-stimulation - when
repeatedly stimulated by constant wind, the leaf would stop reacting.
Sand and soil dust sprinkled on the leaves both provoked a reaction, however the sand made the leaf
close up faster than the soil. If the sand can be assumed to contain a small amount of salt in it, this
could support the salt theory proposed from the salt water test.
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
Grass was growing well underneath the plant, which would have provided some cover for the Skink
to approach the cricket unseen, a good example of the variety of ways wildlife interact with this
plant. One reason the grass was growing really well under the Mimosa pudica plant, is that the
Zebu do not like eating Mimosa pudica.
A possible explanation for ants using the base of the bud to hold onto could be that they feel
more protected being on a plant that has small thorns and along with the plants’ unique defensive
systems, the plant protects itself and possibly the insects as well.
It didn’t appear to be inhibiting any other plants in the area, such as the Black Berry Rubus fruticosus in
Mount Lofty Ranges in South Australia. They grow vigorously by creeping up other plants and strangling
them. The Mimosa pudica didn’t show any signs of affecting other plants growth like weeds we have in
South Australia.
Summary
The Mimosa pudica is a pan-tropical weed all over the world due to its hardiness and ability to survive
all the elements. By undertaking a number of different tests on this plant, we have shown how tough
it really is. It is host to a number of different species in Nosy Be due to its ability to cope with the
traffic of people and Zebu. It isn’t currently growing in primary forest or threatening any other plant
species at this stage.
Overall I strongly believe that the Mimosa pudica is very important to the ecosystem of Nosy Be,
Madagascar. It gives a home and food to many different types of vertebrates and insects. It is only
growing in disturbed areas that are near pathways; cleared forest areas and rice paddies.
It wasn’t overcrowding any other plants apart from the grass growing underneath it; the grass is
not an indigenous species of Nosy-Be, it is of great importance to the native Madagascans who use it
to treat allergies and stress. It is also benefiting the area it is growing in (Frontier survey site known as
5.5), as it attracts butterflies and serves as a host plant for butterfly larvae. The butterflies who
pollinate other plants. The plant also encourages birds to the area like the Drongo- Dicrurus
forficatus.
If the Mimosa pudica was removed, the breeding cycle of the butterflies may be disrupted and could
result in those species declining or completely disappearing.
Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)
References
Bordieu, Michel; Miquel, Jerome, 2013. Nosy Be La grande ile & ses soeurs.
Encyclopaedia Britannica website, accessed on the 6/10/13
www.britannica.com/EBchecked/topic/583199/taproot
Journeys International website accessed on the 6/10/13, www.journeys.travel/info/nosy_be
Kew Botanical Gardens website, accessed on 6/10/13, http://www.kew.org/plants-fungi/Mimosapudica.htm
Plant Scientist website accessed on the 6/10/13,
http://plantscientist.wordpress.com/2013/05/11/mimosa-pudica-a-rapidly-moving-plant/
Rum Gallery Website accessed on the 7/10/13,
http://www.rumgallery.com/_Media/madgascar
nosy_be_map-blk-.png
University of Cambridge website accessed on 6/10/13,
www.sebiology.org/publications/bulletin/july05/salinity.html
West Virginia University website accessed on the 6/10/13, www.caf.wvu.edu/~forage/growth.htm
World Plants website accessed on the 7/10/13, www.candaplants.ca/display.php?id=2721