Okay thank u so much for that info.That look like green chard, most food references will say it's bad for the oxalate content. I don't agree with that assessment. But iI would limit the amount used to no more than 5% of the total greens fed at any one meal and not use it for more than two meals a week, and I would focus on just using the green part of the leaf.
Adults are a better candidates for eating this than babies. Adults could get the whole leaf, green and white parts, but still in the limited amounts.
https://ndb.nal.usda.gov/ndb/foods/show/11147?fgcd=&manu=&format=&count=&max=25&offset=&sort=default&order=asc&qlookup=chard,+raw&ds=&qt=&qp=&qa=&qn=&q=&ing=
On this chart you can see that the calcium is present at 24 mg/100 grams and the phosphorus is 22 mg/100 grams. This is often expressed in a ration C: P of 24:22, that is marginally okay. Most greens offered should have a much higher amount of C to P. Often the recommend amount would be 2:1 or even as high as 30:1 depending on what resource (thing to read) you find.
The reason why I say it's okay, even with a mediocre C: P ratio is at a low amount in the diet you are offering your tortoise variety, and variety offers some enrichment. Enrichment is good too.