Swiss chard or simply chard refer to a green leafy vegetable with two main cultivars, the Flavescens-Group and Cicla-Group. It has other names including silverbeet, perpetual spinach, seakale beet, leaf beet, or beet spinach.
The Flavescens-Group has longer and bigger leaf stalks and during its preparation, they are often prepared separately. Usually, "the leaf blade can be green or reddish in color; the leaf stalks are usually white, yellow, or red" 
Nutritionally, chard has carbs, fats, proteins, vitamins A, B complex, C, E, K as well as minerals such as iron, calcium, manganese, magnesium, potassium, phosphorus, zinc and sodium. This makes it a very nutritious veggie you should not miss. What about rabbits, can they munch it?
Can bunnies eat swiss chard?
Yes. Rabbits can eat swiss chard.   However, you need to know it is one of the leafy greens with high oxalic acid together with others such as spinach, parsley, mustard greens, radish tops, and sprouts.
One source warns about giving your bunny this leafy veggie stating that it can make you bunnies to suffer from not only bloating but also colic. An in-depth research did not prove these facts.
Being a veggie with high oxalic acid, if you feed your pet with too much of it, oxalic acid bind with iron and calcium to form their respective oxalates, increase chances of urinary stones, and it has been associated with “tingling of the skin, and the mouth.” However, in small amounts, oxalic acid is totally harmless to human beings and animals.
Therefore, this should not worry you much if you give them this vegetable occasionally and mix with other veggies with low oxalic acid. After all, you are supposed to give this pet at least 5-6 different types of leafy greens.
A chopped cup of 5-6 mixtures of leafy greens including veggie is enough for a bunny weighing two pounds per day. Ensure you only include one high oxalic acid veggie.
As in the case of any other new food, you need to introduce it gradually over a period of at least 7 days. Begin with small quantities and check how your bunny's tummy is going to react after 24 hours.
In case of diarrhea, bloating or gas, discontinue its use and revert to diets your bunny is used to eating. If none, continue increasing the amount until you reach the amounts we have stated. Only introduce one new food at a time.
Secondly, the source should be free of farm chemicals. Also, ensure you wash it thoroughly to get rid of any remnant farm chemicals.
Finally, remember to follow the recommended bunny diet and in its the right proportions. Diet is important in ensuring these animals are healthy - it makes them less vulnarable to diseases.