The most interesting aspect of the family's ecology is the diversity of adaptive life forms. These range from submerged to free-floating, and emergent aquatics to terrestrial plants and to epilithic or epiphytic forms which may be true epiphytes or hemiepiphytic (growing on trees but rooted in soil). Hemiepiphytism is diverse itself, with some species beginning their lives as terrestrial seedlings, then growing skototropically (toward darkness) until they arrive at the nearest suitable tree ( usually a relatively large one which casts a darker shadow) where a physiological change takes place allowing them to grow toward light (Strong & Ray, 1975). They grow as appressed epiphytes on trees or as vines in the canopy. Others begin their lives as true epiphytes, some reconverting to hemiepiphytes by producing long, dangling roots contacting the forest floor below.