ANYONE EXPLAIN WHERE THIS STAGE COMES FROM?

ANYONE EXPLAIN WHERE THIS STAGE COMES FROM?

Observation - ANYONE EXPLAIN WHERE THIS STAGE COMES FROM? - UK and Ireland. Description: Can't describe it better than in the picture! (don't have the vocabulary) except to say this bit is about half an inch on a three/four inch stem. I know this is the reproductive stage of Horse Tails (with spores) but where does it come from if the next

Can't describe it better than in the picture! (don't have the vocabulary) except to say this bit is about half an inch on a three/four inch stem.

I know this is the reproductive stage of Horse Tails (with spores) but where does it come from if the next stage is sterile? Is there an underground system / rhizome . . . or what?

Is there a way of knowing which variety this is, either at this point or from the more familiar plants (with green spikes sticking out from whorls)?