The Lilypad of Fertility is an item from the Xeno's Reliquary mod. Placing the Lilypad of Fertility within a 9x9x6 area (vertically speaking, one block below, the block the Lilypad of Fertility occupies, and up to four blocks above the lilypad) next to crops will cause them to grow faster. It can be found relatively commonly in Battle Towers, most often from the top/final chest. While in an inventory or while being held, the Lilypad of Fertility has the same shimmer as an enchanted item.
Their effects do stack, so if their areas of effect overlap, the plants in their combined area will grow faster. This can be used to condense your farm into a very small area by surrounding blocks of farmland with up to eight Lilypads of Fertility.