Host specificity in vascular epiphytes: a review of methodology, empirical evidence and potential mechanisms

A considerable number of plants depend on structural support by other plants. To understand their diversity and ecology, it is essential to know how strongly potential host species differ in their suitability as hosts. A new review in AoB PLANTS by Wagner et al. focuses on vascular epiphytes, i.e. structurally dependent plants that do not parasitize their hosts. Despite a longstanding interest in the topic, knowledge on the strength of their host specificity is still scanty. This is arguably due to conceptual confusion, but also because of the large complexity of the study system, which makes quantifying host specificity in the field rather challenging. The authors conclude that future research should use a more comprehensive approach by (i) determining the relative importance of various potential mechanisms acting locally and (ii) testing several proposed hypotheses regarding the relative strength of host specificity in different habitats and among different groups of structurally dependent flora.