Whew, I have been searching and have learned a bit.
Still don't have an answer, but you could start by looking at
Bambusa vulgaris 'wamin' aka Giant Buddha's Belly Bamboo aka Lumpy Noodle, or
Bambusa ventricosa aka Small Buddha's Belly Bamboo
(the 'giant' and 'small' refer to the size of the bulge in the culm, not the size of the plant).
One thing I have learned is that the 'belly' or swollen part of the stem occurs when the plant is stressed. Perhaps the plant in the photo was purposely put under stress to produce a desired effect?
I still don't know much but am having fun looking!
Ahah - Now I think it is more likely this one:
Phyllostachys heterocycla On this link:
http://www.botanic.jp/plants-k... it says ""Kikko-chiku" (Phyllostachys pubescens var. heterocycla) belongs to the family Poaceae (the Grass family). It is a mutant of "Moso-chiku" which is native to southern China. The internodes of underneath culms are swollen alternately, and form hexagonal shapes. It is often planted as an ornamental bamboo in gardens, and it is famous as a fancy bamboo of Kyoto."
Link:
http://www.takehei.jp/global/t...
