You have already come to know about the three basic kinds of tea plant. However, the classification of tea plants has been done by the botanists based on the terminal plants of each race. Tea plant is essentially an out breeding crop and its all three races are highly interfertile. It is believed that free hybridization occurred among the three races even under the natural conditions before tea was cultivated. This happened perhaps because of geographical proximity of the three races of tea and migration of the inhabitants of South East Asia who made use of tea in some form or other. Even hybridity among the cultivated population of southern China was seen. Similarly, the indigenous Assam tea plants discovered proved to be of mixed origin. In N.E. India, cultivation of imported China plant and the indigenous Assam plant side by side extended the scope for hybridization giving rise to innumerable hybrid forms. Now you may understand that truly it is not possible to find genetically pure China or Assam or Cambod tea plant. The existing tea plants under culivation in different countries are mostly hybrids resulting from assamica and sinensis crosses, with introgression of characters of the Cambod form. Even the process of hybridization apparently did not confined to the three races of tea; it extended to other related species resulting in some species hybrids.Camellia irrawadensis is an example. It is across of tea with irrawadensis.
The hybrid forms now we designate as the Assam or China type based on the shape, size and colour of leaf, nature of the bush frame and its size. For example, those hybrids which have more similarity towards Assam tea (C.assamica), we designate them as Assam type and those having more similarity towards C.sinensis as China type. The term China hybrid is commonly used to designate hybrids with leaves larger than those of extreme China type.