It looks like Mare's tail or Horsetail weed. It is an ancient plant. Nearly impossible to get rid of once you have it unless you are constantly on top of it. It has a mother root deep in the ground so topical weed killers don't help much. Also, it has spores. It loves moisture so your mulch is helping it out. It also likes poor soil.
I battled this for three years when I bought my current house. I removed all the mulch. I enriched the soil. I dug out what I could. TWICE a day then I would go around an pluck any new growth putting it in a plastic bag and in the trash. It also was in my lawn. All I could do there is pluck it. I don't see it now. But I keep a close eye for it.
Some people don't consider it a weed. It is my most hated plant after Chameleon plant.
