Narumi Nakato

Cytotaxonomic study of ferns of Yunnan, southwestern China

A cytotaxonomic study was made of 90 fern species of Yunnan, southwestern China, based on collections from northwestern, central, and southwestern Yunnan and a few Chengs collections. The results verified most of the formerly reported basic chromosome numbers of Chinese genera, and recorded for the first time the basic numbers ofGymnogrammitis andSorolepidium and Chinese members of several other genera. Cytotaxonomy of some problematical genera was discussed. Biogeographical relationships between Japanese, Chinese, and Himalayan ferns were compared with special reference to local cyto-reproductive variations inConiogramme, Deparia, Onychium, andPteris cretica. The present evidence indicates that most triploid species examined are agamosporous, as general in filicalean ferns, and also suggests the sexual 32-spored sporogenesis inHypodematium crenatum andSorolepidium graciale as in Lindsaeaceae.

Evidence for Hybrid Origin and Segmental Allopolyploidy in Eutetraploid and Aneutetraploid Lepisorus thunbergianus (Polypodiaceae)

Abstract Several cytotypes (polyploids and aneuploids) have been reported in Lepisorus thunbergianus. The relationships between these cytotypes within the species remain poorly understood. We studied populations in an area where various cytotypes of L. thunbergianus as well as two diploid species, L. angustus and L. onoei, candidate parental species that may be involved in allopolyploid origins of L. thunbergianus polyploids, occur. We determined the ploidy levels of sampled materials by direct chromosome counting and flow cytometry. We elucidated the origins of L. thunbergianus polyploids by analyzing allozyme polymorphisms, and in addition, we examined the occurrence of segmental allopolyploidy by comparing allelic variation between polyploids and their parental diploids. Six cytotypes, i.e. one diploid (2n = 50), two triploid (2n = 75 and 76) and three tetraploid (2n = 100, 101, and 102) cytotypes, were observed in L. thunbergianus, and the two diploid species, L. angustus (2n =52) and L. onoei (2n =50) were confirmed to include a single cytotype each. Allozyme analyses indicated that the tetraploid (2n =100) and hypertetraploid (2n = 102) of L. thunbergianus originated by allopolyploidy between diploid L. thunbergianus (2n = 50) and diploid L. angustus (2n = 52), since the polyploids shared alleles with these two diploids that were unique to each diploid. The allozyme patterns excluded the possibility that L. thunbergianus polyploids originated from L. onoei. The unbalanced heterozygosity and homozygosity found in the tetraploid and the hypertetraploid of L. thunbergianus indicated their segmental allopolyploidy.

The systematic position ofAsplenium cardiophyllum (Aspleniaceae)

Asplenium cardiophyllum is a morphologically unusual species with simple leaves and anastomosing venation, and is often placed in the segregate genusBoniniella. To determine its systematic position, character comparisons were made of vascular anatomy, raphides in leaf epidermis, chromosome number and perispore of this species and those ofAsplenium sect.Hymenasplenium. Asplenium cardiophyllum conforms with sect.Hymenasplenium in its dorsiventral dictyostele, the presence of raphides, a chromosome number of 2n=156 (x=39), and lophate peristore with spinulate projections on the lumina. We therefore propose to includeA. cardiophyllum in that section.

The use of matK in Ophioglossaceae Phylogeny and the Determination of Mankyua Chromosome Number Shed Light on Chromosome Number Evolution in Ophioglossaceae

Abstract The chromosome number and phylogenetic position of the monotypic eusporangiate genus Mankyua (Ophioglossaceae), which shares peculiar morphological characteristics with Ophioglossum s.l. and Helminthostachys, were determined. Meiotic and mitotic chromosome observations of Mankyua show n = 130 and 2n = ca. 260, suggesting that the base number of this genus is x = 130, which is a new finding and the highest base number reported so far for Ophioglossaceae. The molecular phylogenetic trees derived from nucleotide sequence variation of rbcL and matK genes differ in terms of the phylogenetic position of Mankyua. The molecular phylogenetic trees based on combined data sets of rbcL and matK suggest that Mankyua might be the earliest-diverging lineage of Ophioglossaceae.

Two types of partial fertility in a diploid population of the fern Thelypteris decursive-pinnata (Thelypteridaceae)

Two types of abnormal sporophytes were observed in a population of diploid Thelypteris decursive-pinnata. Most sporophytes in this population exhibited regular chromosome pairing, resulting in the formation of 30 bivalents in meiosis I; however, they produced abortive spores to various degrees. Some formed large globose spores at low frequencies, most likely to be unreduced diplospores. The other type of abnormal sporophyte underwent synaptic failure to form 60 univalents at meiosis I, but produced fertile spores, mostly large globose ones at low frequencies. The globose spores were considered unreduced diplospores because the gametophytes arising from them produced tetraploid sporophytes by gametophytic selfing. One tetraploid formed only univalents at meiosis I. Allozyme variation was not detected in this population, although neighboring ordinary diploid populations exhibited it to a certain degree. The sympatric occurrence and allozyme uniformity of the two groups suggest that both are offspring of a founder sporophyte, which may have possessed two types of mutated recessive genes responsible for the spore sterility and the synaptic failure in meiosis. Unreduced spores formed by these two types may play an important role in the polyploid speciation of this species.

Monachosorum arakii Tagawa (Dennstaedtiaceae) is a Relict “International” Hybrid: A Reassessment of the Monachosorum Species

Abstract Monachosorum arakii Tagawa is a plant species endemic to the western part of the main island of Japan. It is characterized by large bulbils on the rachises and is a close relative of M. henryi Christ, which can be found in the Sino-Himalayan region and is not present in Japan. Although M. arakii was reported to be a hexaploid, we determined that it is a pentaploid based on chromosome counts. All of the herbarium specimens examined, including the holotype, had irregularly shaped spores, suggesting that this is a sterile hybrid species. Analysis of the nuclear gapCp sequences also supported its hybrid origin from M. henryi (tetraploid) and M. nipponicum Makino (hexaploid). It should be noted that the parental species of M. arakii, which are endemic to Japan, only co-occur in China. It is possible that the hybrids are relicts from the time when M. henryi were also present in Japan, and are now reproducing only vegetatively by rhizome division and bulbil production. The updated taxonomic treatments for Monachosorum species provided in the current study recognize four species and two hybrid taxa.