"But the most remarkable plant in the forest of Canelos is a gigantic Equisetum , 20 feet high, and the stem nearly as thick as the wrist!...It extends for a distance of a mile on a plain bordering the Pastasa, but elevated some 200 feet above it, where at every few steps one sinks over the knees in black, white, and red mud.  A wood of young larches may give you an idea of its appearance.  I have never seen anything which so much astonished me.  I could almost fancy myself in some primeval forest of Calamites , and if some gigantic Saurian had suddenly appeared, crushing its way among the succulent stems, my surprise could hardly have been increased.  I could find no fruit, so that whether it be terminal, as in E. giganteum , or radical, as in E. fluviatile , is still doubtful, and for this reason I took no specimens at the time, though I shall make a point of gathering it in any state."
(pp. 205-206)

     "The track lay mostly along nearly level ground, with a high cliff to our left, and the Pastaza roaring along its base.  In one part we had to wade for nearly a mile through fetid mud in which grew beds of gigantic horse-tails 18 feet high, and nearly as thick as the wrist at the base"
(p. 157)

     Thus wrote  Richard Spruce ¹ (from Notes of a Botanist on the Amazon and Andes , 1908), the celebrated English botanist and "perhaps the greatest botanical explorer of the nineteenth century" ( Moran, 2000 ) , describing his remarkable encounter with giant Equisetum in Ecuador.

1.   More biographical information from Alfred R. Wallace's introduction to "Notes of a Botanist on the Amazon and Andes"