Common names include horsetail and scouring rush (though it isn’t a rush/Juncaeae.) Spreads vigorously when happy, so in a garden best grown in a pot without drain holes that would allow escape. It’s a truly ancient plant.

Nailed it. I did not know there was such a plant that reproduces by walking, hopping spores that look like 4 legged spiders. That is one of the craziest things I have seen in plants, and plants are chock full of surprises. I read about the spores and i was so incredulous, i was compelled to do more research, and damned if it wasnt true.

It's darn hard to believe that they're closer relatives are ferns. So, bizarre, right?

Patches of these along stream near me. Before moving here I had never seen them. They survive scouring floods that wash about everything else away. Deer chew on them regularly.

"Deer chew on them regularly."

Hoo boy!! I wish that was the case here! Horsetails are a serious weed in my area and very difficult to control or remove. And we have a large deer population......but local deer don't care a fig about the horsetails. Nor do they browse on English ivy, as others from the east coast have mentioned and that too is a seriously invasive weed species in my locale. Now if we could only train our local deer to have east coast appetites, life could be good and the seriousness of some weed issues could be lessened :-)

Our deer just seem to much prefer garden plants to any weeds they may find......

If it is E. Arvense, liming the soil to PH 7-8 should make a difference, as it prefers an acidic soil. Common deer may be controlled with lead travelling at high velocity, as they prefer lower levels of lead in their environment.

" as it prefers an acidic soil. "

As do the vast majority of all other plants! Raising your pH to that level will seriously limit whatever else you may want to plant as well as being difficult to maintain for any length of time if your natural pH is much lower.

I live on an island. Deer are a captive audience here and there is no hunting allowed, although the Fish and Game guys do cull the herds occasionally.

Interesting your deer don't eat ivy, GG. Ours do. In winter especially you'll see where they've browsed ivy on wind thrown trees.

Give our deer a few thousand years to adjust to the non-native vegetation, I'm sure they'll comply when the world is covered in kudzu, honeysuckle, and ivy.

floral, I wish they would browse the ivy but I've seen no sign of it. But then there is SO much ivy growing in this area it would take a majorly sized herd of deer to make much of a dent...or even leave much visible evidence. And it has also been my experience that deer in different parts of the country/world have very different appetites. And I think the severity of winters also plays a factor....here there are plentiful alternate food sources all through winter so perhaps they leave any ivy to the very last choice on the dinner menu :-)

The species in my wood is Roe deer. They also like winter cereals and canola both of which are green and plentiful in winter. But they still go for ivy if it's there. They'll eat holly too if its young and tender.