By surface area:

* The Raffia Palm (Raphia farinifera): This palm has the largest leaf surface area in the world, reaching up to 25 square meters (269 square feet)!

* The Traveler's Palm (Ravenala madagascariensis): This palm has very large, fan-shaped leaves that can reach 5 meters (16 feet) in length.

By length:

* The Royal Palm (Roystonea regia): This palm has long, feathery leaves that can grow up to 6 meters (20 feet) long.

* The Talipot Palm (Corypha umbraculifera): This palm has massive, fan-shaped leaves that can reach up to 8 meters (26 feet) in diameter.

By weight:

* The Giant Water Lily (Victoria amazonica): This aquatic plant, though not a tree, has the largest leaves by weight, reaching up to 3 meters (10 feet) in diameter and weighing up to 40 kilograms (88 pounds).

So, the answer to your question really depends on what metric you are using to define "biggest"!