All true tea (not herbal infusions, but tea tea) comes from a single species. Camellia Sinensis.
While much debate remains about the indigenous home of tea, it is mostly likely a range between the tropical forests of China and India. This plant, either naturally or artificially (human selection) has been broken down into fairly clear sub-species lines**: Camellia Sinensis Sinensis, Camellia Sinensis Assamica, and Camellia Sinensis Cambodgiensis.
Camellia Sinensis Sinensis is fairly distinct form of small pinnate shaped leaves. While all Camellia Sinensis will grow into a tree, Sinensis offers a more shrubby nature with more branching noticed. Traditionally found in China, this variety is found all around the world now. It is particularly useful for crosses between the Assamica variety.
Camellia Sinensis Assamica is also fairly distinct, with larger more broad shaped leaves. This too will grow into a tree, though short, Assamica doesn’t quite develop the branch structure.
Cambodgiensis is most likely a hybridized form between these two more prominent sub-species/cultivars. However due to the wide-spread nature of it, and its presence in the wild, it is also worth mentioning.
All of these teas belong to the same species, but are fairly distinct and recognizable. Some people have argued that sinensis sinensis has a better flavor than sinensis assamica. I do not agree with such assessments. However I do believe that certain varieties grow best in different altitudes and climates. The major tea producing countries all have government institutions set up to create new cultivars. These cultivars are specifically created to optimize the tea plant with that countries unique growing conditions. A prime example of a successful cultivar, is the Ruby 18 variety created in Taiwan. However as with any mono-culture crop, disease is a constant issue keeping the tea institutes busy turning out new varieties.
**No paper has been published on these different sub-species, and hybridization is very common, but I believe from a Botanist perspective that a successful argument can be made of a sub-species categorization