Welcome to the confusing world of bamboo identification. Assigning a name to a bamboo plant often involves wading into the murky waters where taxonomy and horticulture meet.
I once received a bamboo from a reputable nursery, and when it proved to be something other than what I ordered, the nursery was unable to identify what they had sent me, or understand how the mixup could have occurred. For years in Texas, almost every
Bambusa textilis plant sold was actually
Bambusa tuldoides. Even after the problem was well known, some nurseries continued the practice. One nursery that sold me a misidentified plant acknowledged the problem, but said it was no big deal, as the two species are fairly equivalent. They are not, especially where cold winters are concerned. At a bamboo sale at a botanic garden in Texas, I once saw a plant for sale by a vendor that was labeled
Bambusa tuldoides 'Textilis'. I hope nobody is now perpetuating that name.
When someone receives a plant under one name, especially from a "reliable" source, they usually are biased to believe that is the correct name, so they perpetuate the name, even if it is incorrect. In Texas, I have seen several
Bambusa multiplex forms for sale that carry names that are not found elsewhere. Are these new forms, new names for old forms, or a mixture of both? I do not know the answer. I do believe that this species commonly sports, producing new horticultural forms that can not be easily described by taxonomy.
I think in your case, the preponderance of evidence is pointing toward 'Riviereorum'. Compare your plant with this description:
http://www.efloras.org/florataxon.aspx? ... =200024949
Finally, note the statement on this page:
http://www.efloras.org/florataxon.aspx? ... =200024943
"Most taxa are beautiful ornamental bamboos, but their identification, classification, and nomenclature remain complex and controversial. Many varieties, forms, and cultivars have been published, given new status, and variously combined under the species recognized by different authorities. "
My opinion: Call it 'Riviereorum', but when you come across similar plants with labels, take a look to see what characteristics they possess.
I appreciate your serious interest in correctly identifying your plant, and I wish I had enough knowledge to provide more help in this case.