Accidental epiphytes: Ecological insights and evolutionary implications

Abstract

Vascular epiphytes are an important component of many ecosystems and constitute a substantial part of global plant diversity. In this context, accidental epiphytism, that is, the opportunistic epiphytic growth of typically terrestrial species, deserves special attention because it provides crucial insights into the global distribution of vascular epiphytes and the initial evolution of epiphytic lineages. Even though accidental epiphytes have been mentioned in the literature for more than a century, they have been neglected in most epiphyte studies. Only recently has accidental epiphytism been investigated more thoroughly. Therefore, the aim of this article is to provide a comprehensive review of the ecological basis and evolutionary relevance of this common but largely neglected phenomenon and to highlight open questions and promising research directions. Our central statement—that any species has the potential to grow epiphytically given the availability of suitable microhabitats and successful dispersal—is backed up by a compilation of observations of accidental epiphytes from numerous ecosystems with diverse climates, even including semiarid Mediterranean ones. A variety of arboreal microhabitats and environmental conditions conform to the ecological niche of typical terrestrial species, with the availability of such microhabitats depending on the interaction of local climate conditions, host tree age, and host species identity. Whenever suitable microhabitats are available in tree crowns, accidental epiphytism is limited primarily by dispersal. In an evolutionary context, the conquest of forest canopy represents an ecological opportunity where accidental epiphytes act as links between terrestrial and epiphytic life forms. We discuss two fundamental scenarios with sympatric speciation, selective pressure, autopolyploidy, and allopatric speciation as underlying mechanisms in the transition from terrestrial to epiphytic growth. In conclusion, we argue that accidental epiphytism is a substrate and dispersal‐dependent phenomenon and that, both from an individual perspective and an evolutionary perspective, epiphytism reflects the occupation of suitable but previously unexploited arboreal microhabitats. Acknowledging the fundamental principles that plant growth is opportunistic and that dispersal is a stochastic process can decisively improve our understanding of species distributions and other ecological patterns, as in the case of accidental epiphytism.

IAVS - Membership renewal

“…Such individuals are called "accidental epiphytes", and have traditionally been treated as a curiosity that does not merit much attention. Recently, Hoeber and Zotz (2022) reviewed the available information on accidental epiphytes and developed a framework for the scientific exploitation of this phenomenon. They argued that ignoring accidental epiphytism has been a lost research opportunity, because their study should provide crucial insights into the initial evolution of epiphytic lineages and give important context for a mechanistic understanding of the global distribution of vascular epiphytes in general.…”

Climbing aroids in a Panamanian lowland forest: We should reconsider our categories

“…Another major problem with the application of categories is related to intraspecific variability. As discussed for accidental epiphytes (Hoeber et al, 2019;Hoeber & Zotz, 2022), members of the same species can exhibit different growth forms, for example individuals of terrestrial species can sometimes be found growing epiphytically and normally terrestrial trees may develop as a hemiepiphyte. To capture this variation beyond the anecdotal level, F I G U R E 1 Conceptual graph of the different forms of climbers in Araceae are defined by the site of germination and the resulting ontogenetic changes in root and shoot contact (connections) with the soil.…”

Smoothing out the misconceptions of the role of bark roughness in vascular epiphyte attachment

“…Unlike mistletoes, epiphytes are not parasitic, that is, they do not utilize water and nutrient supplies of the host itself (Zotz, 2016). While growth conditions for root systems of epiphytic plants in tree forks or in humus mats hardly differ from those of terrestrial plants on the forest floor (Hoeber & Zotz, 2022), growth on bare bark poses a suite of particular challenges. On bark, epiphytes cannot develop a deep root system for anchorage like their terrestrial ground‐rooted counterparts (Coutts, 1983; Ennos, 2000).…”