Subspecies of Hypolepis rugosula (Dennstaedtiaceae; Pteridophyta) around the world: morphological and biogeographic perspectives

Abstract

The "Hypolepis rugosula complex" has been the subject of great debate among pteridologists: some have considered H. rugosula a single subcosmopolitan (or circum-Antarctic) species, whereas others have considered it a species-complex, encompassing several species. In the 1920s and 1930s, four geographically distinct varietiesof H. rugosula were recognized. In this work, we present a new taxonomy (with new combinations and statuses, as well as typification and full synonymy), together with complete distribution data for the species, with an infraspecific classification based on morphological and biogeographic perspectives. Hypolepis rugosula occurs in southern temperate regions and high-elevation tropical regions of the Americas, Africa (including Madagascar), Oceania and the Philippines, as well as in some isolated oceanic volcanic islands (e.g., Saint Helena and Tristan da Cunha). Here, 15 geographically distinct subspecies are recognized. All subspecies are geographically segregated from each other, except in New Zealand, where two occur sympatrically—possibly due to two different arrival and colonization times. Four patterns of "indument" (referring to catenate and glandular hairs collectively) are distinguished. Different lineages are successful in their respective habitats; we observed two lineages with different ploidy levels (tetraploid and octoploid). Although long-distance dispersal is the best explanation for the extant distribution of H. rugosula;we do not exclude vicariance as a possible explanation for their occurrence on the land masses that were once united as Gondwana. Therefore, we are assuming that a fern species could remain unchanged for more than 70 Myr, and we are adopting the refugia theory, albeit with a different focus.