Short answers, pulled from the story.
Chard (Beta vulgaris subsp. vulgaris) is a green leafy vegetable also called silver beet, perpetual spinach, seakale beet, beet spinach, and leaf beet. It belongs to the same species as beetroot, which is why the common names can overlap.
The origin of the "Swiss" label is unclear. Some attribute it to early descriptions by botanists Gaspard Bauhin or Karl Koch, though Koch was German, not Swiss. Chard does appear in Swiss cuisine, including in the traditional dish capuns from the canton of Grisons.
Carl Linnaeus first formally described chard in 1753, recording it as Beta vulgaris var. cicla. Its taxonomic rank has changed many times since, and it has been classified as a subspecies, a convariety, and a variety of Beta vulgaris.
A 100-gram serving of raw Swiss chard provides 84 kilojoules of food energy and supplies 122% of the daily value for vitamin A, 50% for vitamin C, and 1038% for vitamin K. It also contains significant amounts of dietary fiber and the minerals magnesium, manganese, iron, and potassium.
Swiss chard has one of the highest oxalate contents among edible vegetables, with 480 milligrams per 100 grams of fresh leaves, roughly half in soluble form. High oxalate intake has been linked to kidney stone formation, cardiovascular disease, and osteoporosis.
In tractate Eruvin 29a, the Babylonian Talmud states that a cooked dish of chard is "good for the heart and good for the eyes, and all the more so for the intestines." A second passage in tractate Berakhot 44b contrasts chard with cabbage, calling chard medicinal rather than simply a food staple.