This plant is an oxygen inhibitor.
In the centre of the Southeastern_Peninsula, West of Outpost Rigel and south-west of Outpost Sirius in a deep valley between steep mountains.
Pretty much centred between Outpost Draco, Outpost Sirius and R1. If you're wandering around swampy ruins, you're too far east.
Usually grows right near a log as in screenshots.
May be used together with the Titan Plant in the synthesis of Agent Z, part of the cure for the plague.