Cytological and Reproductive Studies of Japanese Diplazium (Woodsiaceae; Pteridophyta). II. Polyploidy and Hybridity in the Species Group with Summer-Green Bi- to Tripinnate Leaves

Abstract

Mitotic and meiotic chromosomes were examined in a total of 80 plants representing seven taxa in the Japanese Diplazium with summer-green bi-to tripinnate leaves.Diplazium mesosorum and D. sibiricum var. sibiricum are sexual diploids (2n=82; n=4111); D. chinense and D.squamigerum are sexual tetraploids (2n=164; n= 8211); and D. sibiricum var. glabrum is a sterile triploid (2n=123; meiosis irregular). Diplazium nipponicum includes both sterile triploid and sexual tetraploid populations. The triploid is larger in relation to several morphological characteristics and occurs in more southern regions than the tetraploid. Allozyme analysis suggests that the triploid is a hybrid of recurrent origin between the tetraploid and an unknown diploid. Dip/azium x bittyuense is a sterile tetraploid, and the mitotic chromosome number, meiotic chromosome behavior, and allozyme analysis confirm the working hypothesis that it is a hybrid between D. nipponicum and D. chinense. Apomicts are not found within Diplazium with summer-green bi-to tripinnate leaves, and the taxonomic complexity can be attributed to polyploidy and natural hybridization.

A revised family–level classification for eupolypod II ferns (Polypodiidae: Polypodiales)

“…Characters. -Plants terrestrial; roots inserted radially, non-proliferous; rhizomes creeping or short-creeping, not commonly branched, bearing scales; rhizome scales lanceolate, clathrate, the margins entire, without distinct pubescence; leaves green and not covered in mucilage during any stage of development, spirally arranged, monomorphic, not articulate to the rhizome, closely spaced, sparsely scaly; petioles reddish to stramineous throughout, narrow at the base, not forming trophopods, without conspicuous aerophores, without a petiolar articulation; petiolar vascular bundles two, each with hippocampiform xylem, the bundles distally uniting to form a single U-shaped bundle; laminae herbaceous, 2-3-pinnatepinnatifid, broadest at the base, the apex non-conform, the leaf marginal cells differentiated into nodulose hyaline cells; pinna axes not articulate, sulcate adaxially, lacking a free central ridge; the rachis grooves U-shaped, continuous, the sulcus wall of the rachis continuing as a prominent ridge onto the sulcus wall of the costa, and then departing on the costule of the first basiscopic segment; veins free, terminating before the leaf margin, the vein endings not differentiated; sori dorsal along veins, not terminal, elongate, indusiate; soral receptacle flat; indusia lateral, non-glandular; sporangia with stalks two or three cells wide in the middle; spores monolete, non-chlorophyllous, brown, the perispore echinate, tuberculate, or with broad folds, the folds sometimes perforate; chromosome base number x = 41 (Kato, 1975a;Kato & al., 1992;Takamiya & al., 2000). The count of x = 40 (Kurita, 1960) is unsubstantiated.…”

Two new hybrids of the genus Diplazium (Athyriaceae) from Japan

“…However, for parents of these hybrids, previous cytological studies were well studied by using enough individuals, including type locality and around areas of hybrids ( Ohta and Takamiya 1999 ; Takamiya et al 2000 ). Previous cytological studies reported ploidy levels and reproductive modes of parents as follows: D. chinense , diploid sexual ( Mitui 1968 ) or tetraploid sexual ( Takamiya et al 2000 ); D. deciduum , hexaploid sexual ( Ohta and Takamiya 1999 ; Takamiya 2006 ); and D. fauriei , tetraploid sexual or hexaploid sexual ( Ohta and Takamiya 1999 ; Takamiya 2006 ). In addition, Takamiya (2006) reported D. × tsukushiense ( D. chinense × D. fauriei ) as a tetraploid sterile.…”

“…We assumed that the ploidy level of D. × kanayamaense can be pentaploid sterile, based on ploidy levels of D. chinense (tetraploid) and D. deciduum (hexaploid). We do not expect the existence of diploid D. chinense because Takamiya et al (2000) showed enough cytological data of tetraploid D. chinense , which were derived from the populations that were sampled across the distribution range of D. chinense in Japan. We show the relationships of D. × kanayamaense , D. × tsukushiense and its relatives in Figure 6 .…”

Polyploidy and elevation contribute to opposing latitudinal gradients in diversification and species richness in lady ferns (Athyriaceae)

“…Data were obtained from a variety of sources, including online databases (Global Plants, https://plants.jstor.org; Tropicos, http://www.tropicos.org; IPCN, http://www.tropicos.org/Project/IPCN; CCDB, http://ccdb.tau.ac.il/Pteridophytes/Athyriaceae), herbarium specimens, and cytological reports (e.g. Mehra & Bir, 1960; Walker, 1966, 1973; Tryon & Tryon, 1981; Takamiya et al , 1999, 2000; Takamiya & Ohta, 2001; Praptosuwiryo, 2008; Bir & Verma, 2010), and are available in Table S3.…”

“…Previous studies of neopolyploidy using cladogenetic state-change models only considered two states for species, diploid and polyploid (Zhan et al , 2016). However, infraspecific variation in ploidy is common in plants (Wood et al , 2009); in the Athyrium-Diplazium clade, 5–10% of species have polyploid individuals recorded within one or more diploid populations (Walker, 1966; Tryon & Tryon, 1982; Takamiya et al , 1999, 2000; Takamiya & Ohto, 2001; Praptosuwiryo, 2008; Bir & Verma, 2010). Such cases of polymorphism may represent incipient speciation via polyploidization.…”