This flower is known as Lutki(লুটকি). I have seen this flower at most of the forest around Bangladesh. I haven't seen this flower at plain land ever. Scientific/Botanical name of the flower is Melastoma Malabathricum. The seeds of the plant use to spread by the birds, and it is use consider as a weed.
Color of the flower is somewhere between pink to magenta. Flower has five petals and the lifetime of the flower is only a single day. You can use the petals of this flower to stop the bleeding that caused by leech.
The fruit has millions of small seeds inside and the color is pink/black/magenta. During my childhood we used to eat this fruit(tasteless) while we were playing around the jungle. If you eat the fruit, it will color your tongue and the teeth. May be it's a reason to call this as Datranga(দাতরাঙ্গা). For your information the word melastoma(scientific name) means "Black Mouth" in Greek.
This flower is mostly found at different places of Indian territory and the East Asian zone. Photos for this article was taken from Rajkandi Resere Forest, Moulovibazar. More detail about the plant is available at Melastoma Malabathricum
Updated(18/12/2011): Below photos were taken from Birishiri.
ফুলের জন্য ভালবাসা, আমি বুনো ফুল...