There are no specific contra-indications for the Purslane species Portulaca oleracea (or Portulaca sativa).

 

In the book Botany in a Day: The Patterns Method of Plant Identification, author Thomas Elpel discusses the Purslane Family (Portulacaceae) as a whole.  He mentions that many plants in this family contain some amount of oxalic acid, resulting in a mild lemon-like taste.  The author talks more about oxalic acid in the ‘Medicinal Properties of Plants’ section at the back of the book.

 

In the ‘Medical Properties of Plants’ section of the book, the author notes the following:  “Most plants with oxalic acid are edible, but there have also been cautions that long-term consumption of oxalic acid could block the body’s ability to absorb calcium.  However, wild-plants researcher John Kallas suggests the concern over oxalates arose from a study involving sheep and cows eating very large quantities of oxalate-rich plants.  Human metabolism is very different, and most oxalates are excreted with the feces.  Oxalates will bind with calcium in the digestive tract, making both unavailable for absorption.  … Interestingly, most plants that are rich in oxalic acid are also rich in calcium.” (25)

 

The most important warning that I came across in my research for this paper was the following, taken from Identifying and Harvesting Edible and Medicinal Plants in Wild (and Not So Wild) Places by “Wildman” Steve Brill.  In his discussion of Purslane  (Portulaca oleacea), he says:  “There are other very similar Portulaca species, all edible, and no poisonous look-alikes.   However, spurge (Chamaesyce species), which is poisonous, sometimes grows with purslane.  This reclining plant (spurge) has thin, stringy stems, and white milky sap.  Purslane has no colored sap.  Although the two plants don’t closely resemble one another, watch out that you don’t carelessly include any spurge in your salad.” (26)  (Underline added for emphasis.)