What is "herzgewachse"

Herzgewächse ( German: "Foliage of the Heart"), Op. 20, is a composition by Austrian composer Arnold Schoenberg scored for coloratura soprano, celesta, harmonium, and harp. The text is taken from a poem of the same name by Maurice Maeterlinck. The duration of the work is approximately three-and-a-half minutes, making it the shortest of Schoenberg's works with an opus number. The work is also notable for the extreme demands made on the singer which at one point has to ascend to a high F (pianissimo), nearly two-and-a-half octaves above middle C.