Frost Lotus

Frost Lotus is the highest level herb from the Wrath of the Lich King Expansion requiring a herbalist to be level 450 to gather and can only be found as a node in Wintergrasp and The Conservatory of Life. Other ways to obtain Frost Lotus is by gathering any herbs in Northrend such as Icethorn, Lichbloom or any other herbs as there is a  7.5% chance to drop as additional items except for Frozen Herbs. I repeat, Frost Lotus cannot be obtained from Frozen Herbs.

See below for routes to farm Frost Lotus in wow.

Map of Where to farm herbs at Wintergrasp for Frost Lotus