Camellia sinensis and varieties of tea
Every true tea comes from one plant: Camellia sinensis. Green, oolong, black, white, and pu-erh are all made from its leaves. The differences between them come down to processing, and the single most important variable in that processing is oxidation.
One plant, several types of tea
Camellia sinensis has two tea plant types grown at commercial scale. The var. sinensis is the smaller-leafed Chinese variety, suited to cooler, higher ground; var. assamica is the larger-leafed variety native to Assam, and it produces the robust leaf behind most breakfast blends. Growers also select from hundreds of cultivars for flavour, hardiness, and yield. The variety sets the raw material; processing decides what it becomes.
Oxidation is the reaction that happens when the enzymes in a broken or bruised leaf meet oxygen, the same browning you see on a cut apple. Tea makers control it with heat: applying heat early stops oxidation, and resting the leaf lets it continue. The various types of tea are, in large part, a record of how far that reaction was allowed to run.
Green tea: oxidation stopped early
Green tea is made from Camellia sinensis leaves that are heated soon after picking, by pan-firing or steaming, to deactivate the enzyme before oxidation gets going. The leaf stays close to its fresh state, which is why green tea holds its colour and its grassy, vegetal character.
Oolong: the partially oxidised middle
A common question is whether oolong tea is black tea. The answer is no, and oxidation is the reason. Oolong is oxidised partway, anywhere from roughly 10 to 80 per cent depending on the style. That range is why the category is so broad, running from light and floral (Tie Guan Yin) to dark and roasted (Da Hong Pao). The idea that oolong is black tea comes from those darker styles, though even they stop short of full oxidation. Oolong is defined by that deliberate incompleteness.
Black tea: fully oxidised
Black tea is oxidised completely, which develops the deep colour and brisk, malty flavours it is known for. The main black tea types are usually named by origin, among them Assam, Ceylon, Keemun, and Yunnan. Black tea varieties such as Darjeeling sit at the lighter, aromatic end, while Assam holds the strong, full-bodied end.
White, yellow, and pu-erh
Three more styles round out the picture. White tea is the least handled of any: the leaves are withered and dried with minimal intervention, so oxidation stays low. Yellow tea follows the green tea method with one added step, a slow warm resting that mellows the leaf and turns it the colour that gives the style its name. Pu-erh introduces a different variable altogether. It is fermented by microbes after the leaf is made, either aged slowly over years or ripened quickly over weeks.
Read tea as a spectrum of oxidation and the different type of tea in your cup stops being a matter of names. It becomes a question of process: how the leaf was handled between the plant and the pack.
