Morpho-anatomical studies and evolutionary interpretations of the rhizomes of extant Dennstaedtiaceae

Dennstaedtiaceae is a monophyletic, extant family of ferns with sub-cosmopolitan distribution and ca. 265 species. Rhizome morphology in the Dennstaedtiaceae is relatively well known, yet its anatomy has been poorly explored. We performed morpho-anatomical studies on 26 taxa from eight genera, mostly from Brazil, Japan, and New Zealand. Among the studied species, the main rhizome type is long-creeping with alternate phyllotaxy and a solenostele s. str. The exception is Blotiella lindeniana, which has ascending rhizomes with radial phyllotaxy and a dictyostele. A polycyclic solenostele was found in Dennstaedtia (“Patania”) cornuta, D. (“Patania”) dissecta, and two subspecies of Pteridium arachnoideum. Lateral-line aerenchyma characterized Blotiella lindeniana, Histiopteris incisa, Hypolepis spp., Paesia spp., and Pteridium arachnoideum subspp. The position of sclerified parenchyma in the cortex and pith varied among species. Our data enabled us to hypothesize evolutionary patterns of rhizome evolution in extant lineages of the Dennstaedtiaceae. The “Monachosorideae” has retained ancestral conditions: short-creeping to ascending rhizomes with dictyostele s. str. In the “Hypolepidoideae”, two notable changes occurred in Blotiella and Pteridium (in which the solenostele evolved into a polycyclic solenostele). In the “Dennstaedtioideae”, one notable change occurred in Dennstaedtia (“Patania”), namely parallel evolution with Pteridium (in which the polycyclic solenostele has also evolved). We present illustrations, morpho-anatomical descriptions, evolutionary inferences based on the available phylogeny, and supporting tools for studying the taxonomy, systematics, phylogeny, and paleontology of the group