Like its near relative rose loosestrife, Lythrum junceum, grass-poly requires a moist environment, often growing by seasonal or permanent streams. The flowers in the pictures below where in the splash zone of a small cascade. It is a more delicate plant than rose loosestrife, with stragling, upright, brittle stems, the flowers are smaller and are distinguished by having only 6 stamens (L. junceum has 12).