Cytological and Reproductive Studies on Japanese Diplazium (Woodsiaceae; Pteridophyta): Apomictic Reproduction in Diplazium with Evergreen Bi- to Tripinnate Leaves

Abstract

Mitotic and meiotic chromosomes were examined in a total of 162 plants representing 16 taxa in the Japanese Diplazium, including polymorphic terrestrial species with evergreen bi-to tripinnate leaves. Diplazium hachibnse, D. virescens var. virescens, var. conterminum, var. okinawaense, and two other unnamed varieties, D. kawakamii var. kawakamiii, D. dilatatum var. heterolepia, D. taiwanense, D. x kawabatae (= D. dilatatum x taiwanense), D. X takii (= D. hachipense x virescens var. virescens), and D. x nakamurae (= D. hachibnse X virescens var. conterminum) are apomictic triploids (2n=n=123). Diplazium ammianum and D. esculentum are sexual diploids (2n= 82, n=41) and D. subtripinnaturn is a sexual tetraploid (2n= 164, n= 82). Diprazium dilatatum var. dilatatum includes both sexual diploid and apomictic triploid populations.Cultivated gametophytes of six triploid taxa produced sporophytes apogamously, confirming their apomictic reproduction. All three putative hybrids, D. xkawabatae, D. X takii, and D. X nakamurae, are triploid, apomictic, and fertile taxa, therefore they are not the result of hybridization between known pairs of Japanese Diplazium plants.

Apomixis in the interspecific triploid hybrid fern Cornopteris christenseniana (Woodsiaceae)

“…Thus, in C. christenseniana no 32-spored sporangium typical of apomictic ferns was found. Variations in sporogenesis are also reported in apomictic ferns (Manton 1950;Mitui 1968Mitui , 1982Walker 1979Walker , 1985Takamiya et al 1999).…”

“…Plants producing a larger number of normal spores exhibit higher apomixis ability, even though it is incipient. The frequency of apomixis in most plants examined is also lower than that of Diplazium (7-55%; data from Takamiya et al 1999). However, caution should be applied in evaluating these differences because of different experimental conditions.…”

“…9). The frequency (0-36%) of spore germination and the frequency (0-45%) of apogamy are lower than that (6-76% spore germination; 56-97% apogamy) of apogamous species and hybrids of Diplazium (Takamiya et al 1999). Exceptionally, plant 3 (BGCHYMA3) in Fig.…”

“…Data from cytology, sporogenesis, spore germination and gametophyte culture obtained in this study, combined with field observations in the Fern Garden, show that Cornopteris christenseniana performs apomixis. As described below, it is incomplete or incipient compared to obligate apomixis of species that originated from sterile hybrids of sexual species (Gastony and Windham 1989;Darnaedi et al 1990;Schneller et al 1998) and that of Diplazium, a predominantly apomictic genus (Takamiya et al 1999). No apomictic species is known in Cornopteris, in contrast to other genera with both obligate and incipient apomictic species (e.g., Polystichum) (Vida and Reichstein 1975;Pintér 1995).…”

Phylogenetic analyses place the monotypic Dryopolystichum within Lomariopsidaceae

“…5). In Polypodiales, sporogenesis leading to the formation of 64 spores in a sporangium is by far the most common pattern of sexually reproducing species, e.g., Aspleniaceae (Gabancho et al 2010), Athyriaceae (Kato et al 1992, Takamiya et al 1999), Davalliaceae (Chen et al 2014), Dryopteridaceae (Lu et al 2006), Polypodiaceae (Wang et al 2011), Pteridaceae (Huang et al 2006), and Thelypteridaceae (Ebihara et al 2014). Cases of sporogenesis resulting in 32 spores per sporangium are known from a few Polypodiales ferns but all belong to the suborders Lindsaeineae and Pteridineae, i.e., Lindsaeaceae (Lin et al 1990), Cystodiaceae (Gastony 1981), and Ceratopteris (Pteridaceae; Lloyd 1973).…”