How many species of bracken (Pteridium) are there? Assessing the Chinese brackens using molecular evidence

Abstract

Pteridium (the bracken) is a genus of common and widely distributed ferns throughout the world. The variation patterns of morphology in the genus are highly complex and no consensus has been reached among taxonomists regarding the number of species as well as subdivision of the variable species. To address the question of how many species and subspecies of Pteridium occur in Asia, 75 populations were sampled in Bolivia, China, Japan, Malaysia, Mexico and Peru. Sequence data of three chloroplast DNA regions, rps4-trnSGGA, rpl16 and trnSGCU-trnGUCC and the genotype data of three microsatellite loci were collected. The newly generated sequence data combined with the sequences already available from GenBank for samples from all over the world were subjected to several phylogenetic analyses and species delimitation tests. The results support recognition of two diploid species, P. aquilinum in the Northern Hemisphere and Africa and P. esculentum in South America and Australia. Evidence was found to recognize one Asian tetraploid species, P. semihastatum. The Eurasian occurrences of P. aquilinum can be further subdivided into subsp. aquilinum occurring in Africa, Europe and Asia Minor; subsp. japonicum occurring from East Asia to eastern Europe; subsp. wightianum occurring from central China to Malesia (Malay Peninsula, New Caledonia, New Zealand) and northern Australia. The North American subsp. latiusculum was also found in India. Some local "species" recorded in Flora of China likely represent hybrids between subsp. japonicum and subsp. wightianum.