Biometrics of the sporangia and spores of the Parablechnum cordatum complex (Blechnaceae, Polypodiopsida)

Abstract

Parablechnum is the most diverse genus of Blechnaceae (ca. 65 species), with a pantropical distribution and two centers of diversity, in America and in the Austro-Pacific region. The species are dimorphic, with often erect rhizomes and rhizomatic scales, 1-pinnate fronds, with truncate blade at base, conform apex and stalked pinnae. This group presents many taxonomic problems, needing more detailed studies to resolve these conflicts of separation between species. This work deals with the American complex of P. cordatum in which the species P. cordatum, P. schiedeanum, P. chilense, P. falciforme and Blechnum varians are included. A biometric analysis of sporangia and spores, important taxonomic structures in the distinction of ferns, has been carried out. The data were subjected to a one-way analysis of variance and a discriminant analysis. In addition, the spores were observed under a scanning electron microscope to study their ornamentation. Of the characters we have studied thickness of the arcus, number of cells in the arcus, number of cells in the hypostome and major equatorial diameter of the spore have statisticalParablechnum is the most diverse genus of Blechnaceae (ca. 65 species), with a pantropical distribution and two centers of diversity, in America and in the Austro-Pacific region. The species are dimorphic, with often erect rhizomes and rhizomatic scales, 1-pinnate fronds, with truncate blade at base, conform apex and stalked pinnae. This group presents many taxonomic problems, needing more detailed studies to resolve these conflicts of separation between species. This work deals with the American complex of P. cordatum in which the species P. cordatum, P. schiedeanum, P. chilense, P. falciforme and Blechnum varians are included. A biometric analysis of sporangia and spores, important taxonomic structures in the distinction of ferns, has been carried out. The data were subjected to a one-way analysis of variance and a discriminant analysis. In addition, the spores were observed under a scanning electron microscope to study their ornamentation. Of the characters we have studied thickness of the arcus, number of cells in the arcus, number of cells in the hypostome and major equatorial diameter of the spore have statistically supported taxonomic significance and are therefore useful for species separation.

Morphological and molecular evidence reject conspecificity of Malagasy and Mascarene Parablechnum (Polypodiopsida, Blechnaceae)

“…Spore size, perisporium ornamentation and internal structure are known to be reasonably constant within species, but with considerable variation between species ( Lugardon 1974 ; Tryon and Lugardon 1990 ). There are numerous studies on the spores of the family Blechnaceae and some of these have been used to successfully discriminate genera and species ( Passarelli 2007 ; Passarelli et al 2010 ; Moran et al 2018 ; Silva et al 2019 , 2021 ; Molino et al 2020 ; Wal et al 2021 ). The genus Parablechnum is particularly complicated and the study of spores could be an important element in the delimitation of infrageneric taxa, as has been shown in other studies ( Wal et al 2021 ).…”

“…There are numerous studies on the spores of the family Blechnaceae and some of these have been used to successfully discriminate genera and species ( Passarelli 2007 ; Passarelli et al 2010 ; Moran et al 2018 ; Silva et al 2019 , 2021 ; Molino et al 2020 ; Wal et al 2021 ). The genus Parablechnum is particularly complicated and the study of spores could be an important element in the delimitation of infrageneric taxa, as has been shown in other studies ( Wal et al 2021 ). The spores observed for these two taxa present typical ornamentation of the genus: folded cristate-reticulate perispore with or without filamentous processes ( Moran et al 2018 ).…”

“… Bower 1925 ; Copeland 1947 ; Wilson 1959 ). In particular, there have been specific studies in Blechnaceae where sporangia have been key in the separation of genera and species ( Prada et al 2016 ; Molino et al 2020 ; Wal et al 2021 ). Although we did not find differences in sporangial characters, their characterisation is novel and may be useful in future studies of the genus Parablechnum on a larger scale.…”

“…Sporangia analysis was carried out by scraping the sori of the previously softened and rinsed pinnae. The protocol and terminology followed Prada et al (2016), Molino et al (2020) and Wal et al (2021). Spores and sporangia were mounted directly in water, imaged under the optical microscope and measured with the Piximètre software (Henriot and Cheype 2022).…”