Plants use oxalate to control excess calcium by forming crystals, which serves as a dormant storage mechanism for calcium in seeds.

“oxalate plays for plants one of them is that plants have to control calcium all life has to be needs calcium and needs to control it and have it in the right parts of the right amounts and if soil is very heavy in calcium especially for plants that don't need a lot of calcium plants need a way to kind of control the calcium so making oxalate you can grab excess calcium and make these crystals and things as a way to just kind of set it aside you also need to set aside calcium in your seeds because that becomes a great way to have dormant storage of calcium in a seed and often seeds have a ring of calcium oxalate crystals around the outside of them i've got a nice picture of one with raspberry seeds have the ring of the crystals so when a seed starts to germinate enzymes start being able to break up the calcium and the oxalate so the calcium ion is liberated as a cofactor for enzymes that build you know amino acids and things as the germination process continues and what you have left is the soluble oxalate so if you're if you're soaking your seeds you may be liberating this storage molecule that allows the seed to have the calcium that it needs for growth later so for growth for self protection also oxalates can be used to kill off um funguses because the plants can turn it into into hydrogen peroxide”