Chloe Williams - Adelaide Botanic Garden - BTEC Written Report (E16)

Frontier BTEC Advanced Diploma Written Report

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 (minutes)

21.5 26.5 15.3 10.1

*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 Strength of reaction (ranked from 1 (strongest) to 7 (weakest))

Touch Yes 2 Flame Yes 1 Smoke (using a cigarette) No NA - no reaction Water – Salt Yes 3 Water – Fresh Yes 6 Wind (blowing on the leaves) Yes 4 Dust / Soil on the leaves Yes 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)

Min

ute

s

Discussion

Figure 8: Minutes taken for the 'closed up' leaf on the Mimosa pudica to re-open after being touched

40

35

30

25 Shade AM

20

15 Shade PM

10 Full-Sun AM

5 Full-Sun PM

0

1 2 3 4 5 6 7

Test

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/Mimosa-

pudica.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