It's hard to tell from that photo.

Possibly Phyllostachys nigra 'Henon'. However, the branching looks more like a Bambusa, maybe Bambusa chungii or textilis.

Any more pictures or decriptions?

Kt

Those culms are gray because they are close to the end of their lives; it might help to know what the normal culm color is. My first thought based on the unusual branching is that it's some form of Chusquea, maybe Ch. gigantea. Some form of Bambusa is also a possibility. (I'm ruling out any Phyllostachys based on the unique clustering of small branches.)

Here is a link that might be useful: Ch. gigantea

One more picture, but I'm afraid, it will not give more indications. We've as well seen a very big plant of this kind.
Thanks
Wolf

Thanks for the other picture, but you're right: it doesn't add a lot. A lot of us are mainly familiar with what's available in the U.S. There are dozens and dozens of bamboos in Asia that we simply don't have here, since importation of bamboo is strictly controlled by the USDA. The procedure to bring in new species to the U.S. market involves getting a permit, importing it bare-rooted, and paying for it to be maintained in a licensed quarantine warehouse for a year. You have to be really dedicated and willing to spend a lot of money upfront to do this, so the number of new species getting into the U.S. market is a trickle, and yours could be one of the ones that hasn't made an appearance.

I saw some really amazing and distinctive bamboo in China a couple of years ago, and no one could ID them for me on any of the Bamboo forums when I got back.

Wish I could be more help.

On 'the very big plant', were all of the culms the same colour as these in the pictures above?

Kt

kentuck-
I'm still thinking that the culms in the picture are nearing their end, and that's why they are gray. If you look at the middle of the second photo, there is a culm at the back that has nearly no foliage (and it also and looks like it is topped). I'll be interested to hear what the OP says about culm color.

Kudzu, I agree with what you are saying. I just have never seen that many culms all turning gray at the same time and still have that much green foliage on the branches although in the first pic, you can see some dead branches which is characteristic, at least from my experience with bamboo, of much older culms.

My older culms that turn gray do not have any green growth on them but then I don't grow that many kinds of bamboo so it could be a different variety then I am used to seeing. As you also mentioned, it could be a totally different bamboo than any here in the US.

Sometimes my chungii looks like that after transplanting a single culm. The branches start growing from bare nodes within a few weeks to months.

It would be interesting to know more about the culms or have a close-up of one of the culms to help verify colour or age.

I too am interested in the colour of the large plant.

Kt

kentuck-
I do have several bamboo that can have almost a completely gray culm and still have lots of foliage on it. However, I agree that it is kind of odd to have all of those culms gray at the same time. I was thinking that it may just be that they were all planted at the same time a number of years ago and this is what they have evolved to. I also notice some short, bushy culms that may be new growth at the base of some of the big ones, but can't tell what color those smaller culms are.

To all of you, who have tried to answer my question:
Thank you very much for your participation.
May be I should ask someone from Japan. Do you know of a correspondingh japanese page?
Wolf
P.S.: The big ones we have seen at night, I do not remember theit colour.

If you find out, let us know here. I like the look of the bamboo but as Kuszu mentioned it may be a variety that doesn't exist here in the U.S.

I like the contrast in the colour between the culms and green leaves, but I have to also agree with Kudzu that the culms are probably older ones. Looking closely, the culms have a more 'weathered' or 'aged' look compared to a natural colour.

Kt