During recent years, the white tea manufacturers have been using exact pu-erh tea’s compressing technics to produce white tea cakes, while pu-erh tea producers have also produced their ‘version’ of white tea cakes, eg Moon Light White (月光白) Silver Needle (大白毫). I have spoken to a pu-erh tea manufacturer, he said he had consulted a tea expert in China and they could not clearly define the difference.
There is an obvious difference here: white tea leaves are of 'small leaf species' of Camellia sinensis while Pu-erh bud leaves belong to the 'big leaf species'. They are different biologically and therefore have rather different nature and path during the aging process.
Over and above this apparent difference, there is also an economic interest behind this overlap.
White tea, being one of the 'small leaf species' of Camellia sinensis, have predominantly been produced and consumed fresh. Similar to their green tea cousins, the bud leaves are considered of the highest quality and their quality hierarchy is ranked based on the quantity of bud leaves contained.
There has been an aged white tea culture in the local tradition (Fu-Ding area of the Fu Jian Province), but mainly for their medicinal properties. White teas have been described as: first year a tea, third year a medicine and after five years they become a (medicinal) treasure. Aged white teas are believed to have profound anti-inflammatory effects and was once used for high temperature relief caused by measles infections before the contemporary medicine.
Pu-erh teas on the other hand, being the 'big leaf species' of Camellia sinensis, are only suitable for consumption after certain level of aging (softening), two years minimum after their harvest for the raw (Sheng) teas. To facilitate the aging process, they have been conventionally compressed into cakes, bricks or Tuo, and normally contain young and mature leaves with some twigs. The most valuable crops are those from the ancient tea tress (most over a few hundred years old), bud leaves, opened leaves and even some young twigs. The focus here is certainly not just the bud leaves.
The traditional Pu-erh tea producers then saw an opportunity: the bud leaves of certain Pu-erh tea trees are not nearly as sought after as the top grade bud only white tea Silver Needle, for example, the cost of the Moon Light White (月光白) bud leaves is only the fraction of the cost of the Silver Needle white tea, but once compressed and aged, is expected to have very similar taste and functionalities as aged white tea if not superior. This somehow marked the birth of the pu-erh tea cakes.