Poplars

Tall trees with typically narrow slender shapes, especially among European varieties, but that can also grow into broader forms. The flowers of poplars appear as dangling catkins, which grow each year in spring. The wide leaves of these trees are notable for growing on narrow, flattened stems, so that they quiver and rustle in even a light breeze (some species are given names like 'trembling' or 'quaking' for this reason).

As the Company of the Ring approached the land of Lórien, they heard a continuous sound of rustling compared to that made by the quivering of the poplar. There do not seem to have been actual poplar trees in Lórien (at least, none are specifically mentioned) so the implication appears to be that the famed mallorn trees had fluttering leaves of the same general kind as those of the poplar.