Originating in Numenor, from whence it was brought to Middle Earth by the Numeroeans, Pipe-Weed is an analogue of tobacco. The flowering plant that it grows from is called Galenas, and was prized by the Numenoreans for the sweet scent of its flowers.
It was first cultivated and smoked by Hobbits, specifically one Tobold Hornblower from the Southfarthing of the Shire, and the best Pipe-Weed is still considered to come from that region.
From the Hobbits, the use of it for smoking spread among Men and Dwarves, and even Wizards, radiating out in particular from the crossroads of Bree, where traders from all those peoples regularly congregated. As such, other common names for Pipe-Weed include Westmansweed and Halfling’s Leaf.