Two days ago at Shatin, I was delighted to find a plant of
Mimosa (含羞草 = 怕醜草) at the riverside. Its distinguishable compound leaves and purplish pink flowers were different from the others.
Let us study some information about mimosa from Wikipedia:
Mimosa (pudica = shy) is a sensitive, creeping annual or perennial herb often grown for its curiosity value: the compound leaves fold inward and droop when touched or shaken, re-opening minutes later. The species is native to South America and Central America, but is now a pantropical weed.
The common names of mimosa can be :
[1]
sensitive plant [2]
humble plant [3]
shameful plant [4]
sleeping grass [5]
touch-me-not.
In is interesting that the stem is erect in young plants, but becomes creeping or trailing with age. The stem is slender, branching, and sparsely to densely prickly, growing to a length of 1.5 m (5 ft).
The leaves are compound, with one or two pinnae pairs, and 10-26 leaflets per pinna. The petioles are also prickly. Pedunculate (stalked) pale pink or purple flower heads arise from the leaf axils. The ovoid heads are 8–10 mm in diameter (excluding the stamens). On close examination, it is seen that the floret petals are red in their upper part and the filaments are pink to lavender. The fruit consists of clusters of 2-8 pods from 1–2 cm long each, these prickly on the margins. The pods break into 2-5 segments and contain pale brown seeds some 2.5 mm long. The flowers are pollinated by the wind and insects. The seeds have hard seed coats which restricts germination.
Mimosa pudica is well known for its
rapid plant movement. Like a number of other plant species, it undergoes changes in leaf orientation termed "
sleep" or nyctinastic movement. The foliage
closes during darkness and
reopens in light.
The leaves also close under various other stimuli, such as
touching,
warming,
blowing, or
shaking. These types of movements have been termed seismonastic. The movement occurs when specific regions of cells lose pressure, which is the force that is applied onto the cell wall by water within the cell vacuoles and other cell contents. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole. This characteristic is quite common within the Mimosoideae subfamily of the legume family, Fabaceae. The stimulus can also be transmitted to neighboring leaves.
It is not known exactly why Mimosa pudica evolved this trait, but many scientists think that the plant uses its ability to shrink as a defense from predators. Animals may be afraid of such a fast moving plant and would rather go and eat a less active one. Another possible explanation is that the sudden movement dislodges harmful insects.Mimosa pudica is native to South America and Central America. It has been introduced to many other regions and is regarded as an
invasive species in Tanzania, South Asia and South East Asia and many Pacific Islands. It is regarded as
invasive in parts of Australia and is a declared
weed in the Northern Territory, and Western Australia although not naturalized there. Control is recommended in Queensland. It has also been introduced to Nigeria, Seychelles, Mauritius and East Asia but is not regarded as invasive in those places. In the United States of America, it grows in Florida, Hawaii, Virginia, Maryland, Puerto Rico, and the Virgin Islands.
The species can be a
troublesome weed in tropical crops, particularly when fields are hand cultivated. Crops it tends to affect are corn, coconuts, tomatoes, cotton, coffee, bananas, soybeans, papaya, and sugar cane. Dry thickets may become a fire hazard. In some cases, it has become a forage plant although the variety in Hawaii is reported to be
toxic to livestock.
On Sunday, July 11th, 2010, before the 2010 FIFA World Cup final soccer match started at Soccer City Stadium in Johannesburg, South Africa, the captain of the Champion Soccer team (Italy) in 2006 World Cup, Fabio Cannavaro (簡拿華路) took out the FIFA World Cup from a box and showed it to the spectators at the stadium.
