The non-fertie segmented stem shich appears after the brown, fertile cone-headed stem dies back.
May be confused with other horsetails. Field Horsetail has long branchlets which are not branched themselves. A hybrid with Water Horsetail may look similar but will have shorter branches. This specimen may be a hybrid or not fully developed stem.
Horsetails can be difficult to identify, especially when the fertile stem has died back, as in this example. The fertile stem of Water Horsetail is green.