Left alone, it is a tree
Camellia sinensis is a woody evergreen that grows into a tree — the assamica variety readily to ten metres or more, the sinensis variety smaller but still well beyond bush height. The waist-high hedge in every photograph of a tea garden is the result of pruning that begins when the plant is young and never stops. The field is cut to a plucking table because a picker has to reach across it, and the plant is kept in permanent vegetative growth because a plant putting energy into flowering and seed is not putting it into shoots. So "bush" describes a management regime and not a botanical fact.
The two varieties, and the shape difference between them
TeaHQ's own reading of well-attested general knowledge, with no single source behind it.
VAR. SINENSIS is the smaller-leaved, cold-hardier variety associated with China, Japan and the Himalayan districts. Multi-stemmed, slower-growing, and long-lived — bushes well over a century old are still in production in several districts. VAR. ASSAMICA is the large-leaved variety native to the Assam–Yunnan–Burma borderlands. Single-trunked, faster-growing, less cold-tolerant, and much larger left uncut. It is the basis of most of the world's black tea. The two interbreed freely and a great deal of planted material is hybrid, which is one of several reasons cultivar names and variety names should not be used interchangeably.
The old trees, and the claim attached to them
Where assamica-type plants have been left unpruned for a long time — parts of Yunnan most famously — the result is genuinely a tree, harvested by climbing, and the leaf from them is sold at a premium as gu shu, "old tree" tea. Two things are worth separating. That old, deep-rooted, unpruned trees exist and are harvested is a fact. That their leaf is intrinsically superior is a claim, and it is one the market rewards strongly enough that far more tea is sold as old-tree material than old trees could plausibly produce. Ages given for individual trees are frequently estimates presented as measurements. The honest position: the material is genuinely different — grown differently, picked differently, in much smaller quantity — and the specific claims made about tree age are among the least verifiable in the tea trade.
Seed, cutting and what it does to a field
A field grown from SEED is genetically varied: every plant is a distinct individual, so shoots emerge at different times and the material is uneven. That suits hand plucking, which selects, and it is what older gardens and Chinese landrace plantings look like. A field grown from CUTTINGS is a clone: every plant is genetically identical, flushes together, and gives uniform material. That suits machine harvesting and consistent manufacture, and it is what most modern planting is. This is the practical meaning of "clonal" on a Darjeeling packet and of a named cultivar on a Japanese one, and it is a real difference in what the field is rather than a marketing distinction.
Why the plant lives so long and what that implies
A tea bush is a fifty-to-a-hundred-year investment. That fact structures the industry: replanting takes a field out of production for years before it yields, so ageing fields with falling yields are frequently kept in production rather than replaced. It is one of the underlying pressures on districts whose output is declining, and it is why a conversation about a garden's future is a conversation about capital rather than about agronomy.