Strange but common in isolated environments: new records of Marathrum (Podostemaceae) in rivers of Colombia

Abstract

Aquatic plants are generally underrepresented in herbaria due to geographic bias, rarity of species, and sampling bias towards terrestrial vascular plants. This constitutes a limitation to various lines of research (e.g., evolutionary and ecological studies) centered around aquatic plants. Plants in the genus Marathrum (Podostemaceae) have been suggested to be under-collected due to their highly modified phenotypes and to geographic bias. Marathrum (and Podostemaceae in general) live attached to rocks in river-rapids and waterfalls, which are difficult habitats to access. Here, we aimed to assess the number of historical records of Marathrum in Colombia, the country where the genus was first collected and where mountain ranges have been found to constitute a barrier to gene flow across populations. We expand past records with new records for the genus in Colombia and find that Marathrum are not uncommon in river-rapids and waterfalls in the country, but their under-representation in herbaria respond to several collection biases. We discuss the reasons for changes in the number of collections of Marathrum in Colombia through time, sources of collection bias in the group, and the relevance of occurrence records of Marathrum. The herbarium data reported in this study are publicly available in a digital repository to facilitate future research.