The Velamen Radicum Is Common in the Genus Anthurium, Both in the Epiphytic and Terrestrial Species

Abstract

The velamen radicum, a rhizodermis that consists of dead cells at maturity, is often described as typical for epiphytic aroids. Such claims are surprising on two grounds: (1) there are hardly any data on this trait for aroids and (2) the link between a velamen and epiphytic growth has recently been challenged in general. We performed an anatomical and histological study with 82 Anthurium species and analyzed the occurrence of a velamen in regard to habit (epiphytic vs. terrestrial) and phylogenetic relatedness. Almost 90% of both epiphytic and terrestrial species had a velamen. The number of cell layers comprising this tissue were also very similar in both groups. The most likely interpretation of the phylogenetic tree suggests that a velamen is not ancestral in Anthurium. It was gained once and has been lost several times during diversification of the genus. Our results are an important contribution to the current discussion on the possible function of the velamen. While there is some experimental evidence for its importance for epiphytic plants, its role in terrestrial plants is completely unresolved.