What is tea?
Tea is a plant, Camellia Sinensis is the name of this evergreen bush. The tea plant can grow up to 60 feet if left to grow on its own accord. However its much easier to pluck tea leaves when they are closer to the ground. This is why in most countries the tea plant is cultivated to a height of 3-5 feet. The plucking table is two leaves and the unopened leaf bud. Up to 80,000 hand-plucked shoots are needed to produce one pound of loose leaf tea.
The difference between the types of tea result from variations in the processing of the leaves after they are harvested. The processing affects flavor, aroma, caffeine levels and health benefits. This is best described by picturing and apple. If you take a bite out of an apple and allow the apple to sit out for a while the apple will begin to change color as oxidation sets in. The same goes for tea. Once the leaf is plucked it begins to oxidize. The farmer can halt oxidation by processing or firing the leaf. The least oxidized teas are the lightest color. A fully oxidized tea is a black tea.
To sum it all up all tea comes from the same plant except herbals and tisanes as they do not come from Camellia Sinensis aka the tea plant.