It looks like Phyllostachys Nigra to me...which is Black Bamboo.

The green culms will turn black the older they get and the more sun they're exposed to.

I agree somewhat, but no rhizome race track like I'd expect for a 5 year old plant in this planter.
Blessings

Looks like my P. nigra also, but my culms won't turn black in full sun, they stay spotted or green as in your pics. They need shade to turn completely black.

Kt

I'd think if anything the blackening would be more pronounced in stronger light, same as with green culms turning more yellow in more sun. Is there something different in this respect about P. nigra (which the above specimen clearly is)?

I had four year old culms at my workplace that got almost full sun and the culms never turned black, they were spotted and the green parts turned more yellow.

The new culms in complete shade, turn black before the end of the growing season, same goes for the P. nigra here at my house. More sun, less black...less sun, more black. May be an environmental thing. This Texas sun gets extremely intense and hot. Possibly a different form of black bamboo also.

Sunlight slows the process and also tends to make the culms spotted instead of solid black.

However, Lako and Atro seem to turn black in shade or sun.

Kt

Haven't noticed this phenomenon here.

I still think its another variety... 5+ years in the planter...never an escapee and when I cut it open...the longest rhizome was 8-10 inches. I'd expect a race track of running rhizomes around the planter manytimes. But none... not one.
any other possibilities?
Blessings,

I've always been led to believe that age + shade encouraged the black culms. Three years, with a bit of shade, and Ph. nigra should go black.

My own Ph. nigra planting is less than a year old....still too young for comparison.

Josh

Possibly P. nigra 'othello'? Mine has been in a pot for a few years and no escapees as of yet, but then I don't give it any extra care...just water it every so often.

Josh, I agree. Age and shade will encourage black culms. In sun, they will never turn completely black, just become spotted. Gib Cooper told me this before I bought mine years ago. He said it needs to be planted in partial shade.

Kt