Tall, green, lobed-leaf (like celery) with red/purple base

This tall (over 5') plant resembles heirloom red celery, but I don't think it is.

It has the coloring of rhubarb on some of the offshoots, but not the same leaves as rhubarb.

It has shallow roots, longitudinal venation; ciliate margin on the leaves and as I mentioned, is over five feet tall now!

I started with one and now my garden is full of them! What is it?


The offshoot looks like celery, but the stem is rounded. ( photo / image / picture from Semilove's Garden )






typical example of this 5+ plant ( photo / image / picture from Semilove's Garden )

 

Reminds me of Helianthus multiflorus
http://www.bluestoneperennials.com/b/bp/HEMFS.html

 

Absolutely NOT a sunflower. This thing looks like celery and has no flower so far.

Funny, but the flowering plants surrounding this ARE what you said although they aren't related at all!