The Erechthites hieracifolia. It is not properly a grass.
1792. The fire-weed, which spontaneously grows on all burnt land. This fire-weed is an annual plant, with a succulent stalk and long jagged leaf; it grows to the height of five or six feet . It never vegetates, except on the ashes of burnt wood.Jeremy Belknap, New Hampshire, iii. 1334. (Partly cited, N.E.D.)
1821. Immediately after the fires, a species of grass springs up, sometimes called fire grass, because it usually succeeds a conflagration.T. Dwight, Travels, iv. 61.
1857. There were great fields of fire-weed (Epilobium angustifolium) on all sides, which presented great masses of pink.H. D. Thoreau, The Maine Woods, p. 262 (1864).