Gavid

The Plant King (rumored to be named Gavid The Plant King) was cancelled due to not fitting well within League of Legends artistic theme.

On the map for the 2010 Harrowing, a coffin can be seen on the extreme lower right with him in it. This could be a subtle "nail-in-the-coffin" confirming his cancellation.

It is very likely that "Plant King" was scrapped in favor of who may have been more appropriate to League of Legend's style.

Abilities
Although no official statement was given on the Plant King, there are some images inside the game files about his abilities:

Trivia

 * The ability icon for has been reused for the  buff, which is obtained from killing  on The Twisted Treeline.