RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Jangerberries
The Old School RuneScape Wiki also has an article on Jangerberries.

Jangerberries can be found on a small Ogre island west of Yanille. They are a secondary ingredient for making a Potion of Zamorak. These berries are also used during the Watchtower quest as an ingredient for the Ogre potion.

Effects when eaten

Boost your Attack level by 2, your Strength level by 1, restore your Hits by 2, and restore your Prayer points by 1.

Item spawns