[Ledasmom]

All lettuces of which I am aware are Lactuca sativa; your mesclun mix should be fine, as long as it's an all-lettuce mix - iceberg is rarely a component of mesclun. If it's a mixed-green mesclun with other species, you would want to look up those species to make sure they were acceptable. If you harvest the leaves at a young age, as is commonly done with mesclun, the oxalic acid content of such plants as spinach would be considerably lower than in the mature form, though I would think you would still want to avoid feeding them every day.