Before I begin what is a long post, let me say that of the 9 guesses I received, we had a winner! Unfortunately, said winner chose to post anonymously. For your information, the teas were, from top left to bottom right: young sheng, 90s dry stored sheng, 90s wet stored sheng, young shu, and 90s wet stored shu. This leads into a discussion: what does the appearance of the leaves reveal?
Dry Leaf Appearance
As the guessing game results imply, tea leaf appearances can be deceiving. There are a couple of generalizations that hold true:
Young sheng leaves are green, often shiny, and have visible fur on the tips and even the larger leaves. Some examples are below.
Dry stored sheng ranges in color from greenish brown (10 to approx. 15 years) to medium brown (15+ years) to medium dark brown (25+ years, if you can find it! This is very rare tea indeed.). It is often shiny, and fur is often visible in the larger leaves and always visible on the tips. Some examples are below.
Wet stored sheng is medium to dark brown, often with a golden brown tinge. Often there is visible white frost from mold growing on the leaves, though occasionally the teas are brushed or baked to improve its appearance. It often has a matte finish except for the bud tips, which show the only visible hairs. Sometimes, wet stored sheng also has small yellow spots of mold.
Young shu is dark gray-brown to gray-black, highlighted with golden bud tips if any are in the blend. The composting process breaks the outside of the leaf down, resulting in a matte finish that seems like a fine gray powder is covering the leaves (in shu fermented for extremely long periods, this results in a yellow-gray powder coating). Composting also makes the tea leaves appear indistinct from one another compared to sheng, whose leaves are more obviously separate.
Wet stored shu, like young or dry stored shu, has less distinct leaves, a matte finish, and a dark brown or black color with a grayish powder tone. However, the wet storage often makes the tea appear even more matte and gray than with younger or dry stored shu, and like wet stored sheng, mold can appear as white fuzz or tiny yellow spots. I only have one example to give (sorry!) because this tea is pretty rare in the Western market.
Caveats: there are degrees of wet storage and dry storage. Marshaln, for example, discusses "traditional" hong kong storage and explains it as a period of wet storage (2-3 years) followed by a long period of "dry" storage, yet tea is available in Hong Kong that is much wetter than a "traditional" storage might imply. Also, "dry" storage in Taiwan is going to be wetter than dry storage in Kunming, simply as a factor of average relative humidity being higher in the former.
Brew color and color development
Another way to tell these teas apart is in the color development across infusions. Traits to look for aside from color is depth and clarity. The chart below covers the first ten infusions of the five teas I asked my visitors to guess. All were brewed in the same gaiwan using exactly 7g of dry leaf measured in a scale accurate to less than .1g.
While again, there is a lot of variance, the tropes below become more easily understood when evidenced in reality.
Dry stored sheng and shu tend to be deep in color but clear, particularly older dry stored sheng; wet stored sheng and shu tend to be deep and not clear; the wetter the storage, the less clear the liquor. Sometimes the fine powder of wet stored teas can be seen dried on the side of the cup (I should have tried to photograph this. Maybe I'll edit this post later!).
Shu teas and wetter stored sheng tend to "hit the wall" and lose their depth of color quickly, while younger sheng and dry stored sheng maintain a very consistent color across infusions. You can see the 05 shu hit the wall at infusion 8, so i pushed it a tastier 9th infusion. The wet stored shu hit the wall at infusion 9, so I pushed it to get a tastier infusion 10. The change in the wet stored sheng, however, was more graduated before hitting the wall at infusion 9, again pointing to consistency with sheng tea.
Shu teas are slightly more purple-red than sheng, but brew color is generally not enough to tell a wet stored sheng from a shu. For example, wet sheng infusion 10, 05 shu infusion 8, and wet shu infusion 9 are nearly identical in color tone, depth, and clarity.
Taste is the most obvious indicator of differences across these genres. In general:
Young sheng is generally bitter, often lingering bitterness that transforms to sweetness after swallowing (at least, amongst better examples of these teas). Individual tastes very widely by the region(s) where the leaves were sourced, size of the leaf, processing, and age of the trees, but common descriptives for this tea include straw, hay, tobacco, smoke, and bright floral notes like jasmine/narcissus. The texture is sometimes astringent/drying.
Young shu generally has muddy earth flavors that end in a mineral water flavor and occasionally a rancid bite. Common descriptives include earth/soil/mud, milk/chalk, lotus root, and in lesser teas pond, fish, cave. There is not much complexity to most shu teas. The texture is soft.
Dry stored sheng shows lessening of bitterness (and smoke, if present when young) as it ages; young dry stored sheng is bitter, but older dry stored sheng is not. The flavors are similar to shu but much cleaner and more complex: earth, forest floor, bark, wet bark, wood, cedar, darker/muted florals like rose. As infusions progress, ~5-20 year-old dry stored sheng tastes "younger": the flavors tend away from "aged" flavors on the wood/earth spectrum and more toward the flower/hay flavors of younger teas. The texture varies as it ages, becoming less astringent and softer over time.
Wet stored sheng shows little bitterness and has much in common with older dry stored sheng in terms of flavor, being earthy. The earthiness can taste less clean than dry stored sheng, and words for this tend to be mushroom, cave/basement, mulch, etc., and it also tends to be slightly less complex. The most distinctive flavor of wet stored teas is the "mei wei" (霉味) or "mold taste", which I liken to the smell of mildew or even bleu cheese. This is usually smelled before tasted, and is also a feature of wet stored shu. This taste often goes away with time in dry storage, as the mold activity in the tea slows (ceases?). The texture is usually quite soft, though some people report very wet teas as making their throats dry and uncomfortable.
Wet stored shu tastes much like young shu insomuch as it shares muddy earth flavors, milkiness, and, in lesser teas, that distinctive rancid bite. However, the wet storage softens these flavors. Wet stored shu can also have mold taste/smell and some of the basement/cave flavors of wet stored sheng, making it in some ways more interesting than dry stored or young shu, although still quite monotone. As with young shu, the texture is quite soft and smooth, but like wet stored sheng, if too fresh out of storage or stored too wet, sometimes it gives the throat discomfort.
Wet Leaf Appearance
The appearance of the wet leaves is often the best visual indicator of pu'er genre and storage condition:
Young sheng: very green, though some strange varietals (wild or purple leaf) can be dark green enough to seem brown. Buds upper flags are tender.
Dry stored sheng: green-brown to medium-dark brown, depending on age. Buds and upper flags are tender. The picture below is 90s tea, hence the leaves show a good deal of green tint to their brown color.
Wet stored sheng: medium-dark brown to black, depending on age and storage condition. Buds and upper flags are not very tender, with very wet teas undergoing "carbonization" into black, leathery leaves that do not fully open or fall apart. This photo shows a 1990s traditional stored tea with medium brown leaves and some carbonized black bits.
Young shu: light brown to black, depending on fermentation level. Most shu teas are blends of leaves of various degrees of fermentation. Leaves are very tender and fall apart when rubbed (see video below).
Wet stored shu: medium-dark brown to black, depending on storage condition. Buds and upper flags are not very tender, with very wet teas undergoing "carbonization" into black, leathery leaves that do not fully open and show signs of structural damage (picture at right). Leaves are brittle and fall apart when rubbed (see video below).
To get an idea of what I mean when I say "fall apart when rubbed", I put together a video of me rubbing the leaves of the dry stored sheng, wet stored sheng, 2005 shu, and wet stored shu:
I hope this is useful for people who are building their knowledge of various kinds of pu'er, young and aged. While this post cannot substitute for experiencing these teas in person, I hope it helps people who are looking at photos on vendors' websites and tea forums or shopping in person for these teas in Asia.
Suffice it to say from the above, telling apart the darker colored pu'er varieties based on dry leaf pictures alone requires a depth of experience and a keen eye. Pictures of brews and wet leaves help, but even then, the photos are only as good as the conditions and camera: all it takes is odd lighting, a low quality digital camera, and/or an incorrect white balance to throw off even the better experienced tea drinkers.