Sheep's Sorrel, Rumex acetosella contains
oxalic acid and spreads easily over poor quality barren soil by its aggressive rhizome. Also it "weathers" clay changing it's structure and improves nutrient availability.
"Organic acids such as malate, citrate and oxalate are involved in many processes in the rhizosphere, including nutrient acquisition and metal detoxification, the alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction (Huang et al., 2010, Jones, 1998, Li et al., 2006, Marschner, 1995)."
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