Lowering oxalates can only be effectively done by extensive boiling of cut up stalked vegetables (broccoli, cauliflower, asparagus, when drained and rinsed that will still provide msot of the calcium that they contain raw which isn't biovailailable.
For leafy greens like turnip greens, bok choy, and Kale that have a positive Ca:Ox ratio, blanching for a few minutes will lowers the alkalinity in support of not over alkalizing the diet as well as oxalates that are on the lower side compared to most other sources.
How oxalates are reduced is by breaking down the cell bonds that allow Calcium oxalate to be flushed out of the cellulose. With leafy greens notably very high in oxalates, like spinach, chard, beet leaves, collards, and some others, boiling can reduced the oxalates by breaking down the cell walls that allow Calcium oxalate to be flushed out, while destroying the oxalic acid of the soluble fraction. Yet this leaves a green glop devoid of water soluble vitamins and nutrients.
When it come to the exceedingly high oxalate leafy greens, that include spinach, beet leaves, chard, garden orach, sorrels, and rhubarb, lamb's quarters, and purslane, the highest of which are noted to contain 1100 to >2000 mg. per 100 grams, reducing the oxalate level of purslane by boiling brings it down by about 500 mg. , yet that left over 1100 mg. of oxalates after boiling.
By far this source is the highest even compared to Rhubarb, which for reason of it's higher soluble oxalics is toxic to mammals. At this level even with the reduction to 1100 mg. with 101 mg. avg. in calcium, this source has an 11:1 ratio of Oxalates to calcium the worst ratio of any food listed as edible. For humans this source could be included infrequently in small amounts in a salad, yet in doing so about 70 % of the calcium in the salad consumed wtih this source would be not be available for supportin bone and metabolic health. Whatis the point in addig a source that contains a high ratio of Ca:P in the plant, when once digested turns into a high calcium demineralizer?
(See chart in PDF for data)
https://www.researchgate.net/publica...ooked_purslane