The broccoli heads which we eat as the vegetable broccoli are actually the flower of the plant. The broccoli family includes calabrese types as well as sprouting varieties. Colours include the regular green, purple and even white.
Broccoli is often thought of as a calcium rich food and yet it not only contains only 44-48mg calcium per 100gm, it also contains 66-87mg phosphorous giving it a poor Ca:P ratio.
It is a good source of vitamin C at 93-121mg per 100gm.
Guinea pigs love the stalks split lengthways into quarters which they chew on with relish.
The outside leaves are by far the healthiest part of the plant for rabbits and guinea pigs and although I can find no listed information on the calcium and phosphorous levels, devoid of flower and stalk I would expect the leaves to have a healthy Ca:P ratio.