Middle Devonian herbaceous lycopsid Haplostigma from the Paraná Basin, Brazil: Taxonomy, biostratigraphy and Phytogeography

Most paleobotanical records from the Middle Devonian consist of stems of herbaceous lycopsids. This group of vascular plants has a fossil record longer than any other group, extending from possibly the Late Silurian to the present day. Newly collected fossil material including lycopsid stems found in the Middle Devonian of the Paraná Basin were analyzed and assigned to the morphogenus Haplostigma and, more specifically, to H. irregularis, H. furquei, H. baldisii, and H. cf. kowiensis. Morphometric analysis based on characters measured on stem supports the taxonomic separation. This represents the highest diversity of this genus reported so far in this and other Gondwanan basins. The stratigraphic record and paleophytogeographic distribution of Haplostigma species in all Devonian deposits were analyzed. Available data indicate that Haplostigma is composed of small to medium-sized, fast-growing herbaceous lycopsids, which were apparently very successful and well adapted to the cool-temperate high-latitude climates during the Middle to Late Devonian.