[cmrdporcupine]

I don't know the exact mechanism (it sounds like nobody does) but remember these are clonally propagated (until they flower, which I presume creates seeds). So most of the entire population is actually one genetic "individual". So the 'alarm clock' must be tied to the original genetic signature.

[Ma8ee]

No, there's no reason to believe they are only one genetic individual. Just because many are clones, there's no reason to believe they all are clones from the same original plant.

[jonknee]

"all plants of the same stock of bamboo" makes it sound like this would indeed be from the same original plant.

[_underfl0w_]

I'm no expert here, but that does seem to be a logical interpretation of what was written.

OTOH, the author seems distinctly... less scientifically inclined than the bulk of commenters here. They may have simply meant "of the same genus".