Hemiepiphytes revisited

Hemiepiphytic plants are defined by their ontogeny. They germinate on a host tree but later establish root contact with the soil. Most hemiepiphytes remain structurally dependent on their host for their entire life, but some, often referred to as stranglers, develop pseudotrunks that allow them to outlive their host. Unfortunately, the terminology used to describe hemiepiphytes and other structurally dependent plants (epiphytes, vines, lianas, nomadic vines, etc.) is highly inconsistent, which causes much ambiguity. Published reports frequently use the term "hemiepiphyte" without providing evidence, and it is often unclear whether conclusions are based on data, casual observations, or conjecture. Moreover, many hemiepiphytic species are facultatively terrestrial to varying degrees, which further complicates classifying them. In order to address these issues, we performed a thorough, critical review of the literature and provide an in-depth account of current knowledge regarding the morphology, physiology, ecology, and evolution of hemiepiphytes. Based on published works and our substantial field experience, we summarize the taxonomic distribution of hemiepiphytes among vascular plants, which includes c. 800 species in c. 30 families of ferns and angiosperms. We identify numerous, promising avenues of research on this fascinating group of plants, and make a case for adopting an explicit and unambiguous approach to describing hemiepiphytes and to naming life forms in research projects, on voucher specimens, and in the scientific literature.