The Greenhands were descended from Holman "the greenhanded", and Holman's namesake and grandson, Holman Greenhand, was at least the third of the line to tend the gardens of Hobbiton. Holman was the gardener at Bag End for Bilbo Baggins, and perhaps also for his father Bungo. In about the year T.A. 2941, he took on his young relation Hamfast Gamgee as an apprentice. Hamfast eventually became the gardener at Bag End himself, and was followed by his son Samwise.
In a curious and unlikely way, Holman was instrumental in the winning of the War of the Ring. One morning in the spring of T.A. 2941, Bag End was visited by the Wizard Gandalf. Bilbo was away from home for the Elves' New Year, so Gandalf struck up a conversation with Holman. It was Holman's description of his employer that encouraged Gandalf to include Bilbo in the journey to the Lonely Mountain, which in turn led to the finding of the One Ring, the means through which Sauron was ultimately defeated. If not for the part of Holman Greenhand, then, the western lands might well have fallen under the yoke of the Dark Lord.