Rangpur Lime or Mandarin Lime is a citrus fruit originating on the Indian subcontinent. It is believed to be a naturally occurring hybrid between mandarin orange and lemons. It looks like an Orange in that it has a radiant orange peel and flesh, some say a tad reddish. It has a highly acidic / sour and taste - lemony . It is called Canton Lemon by the Chinese, Hime Lemon by the Japanese, and sometimes Mandarin lime in North America.
I recall when I was first introduced to this little gem, breaking off a segment much like you would with an orange. It had a sweet aroma which was misleading because when I popped it in my mouth and chewed on it the sour pucker power was overbearing. I have no problem sucking on a lemon, but there is some psychological factors at play when you think you're getting a sweet treat and get blasted with the polar opposite.
Rangpur is grown as an ornamental tree and as a container tree on patios and balconies and is also used as a rootstock for many grafted citrus trees. In Central America, particularly Costa Rica, where it is favored over Lemons and limes and grown commercially.
The mature trees can reach upwards of 20 feet but take quite a few years to attain such a height, and then generally only in tropical regions. They ahve thorns similar to Orange trees. The fruits are fairly small to medium and sometimes mistaken for tangerines.