Potamogeton × apertus Miki is a putative natural hybrid between P. pusillus L. and P. oxyphyllus Miq., recognized in 1935. However, after being recognized, information on the hybrid was scarce, and it was thought to be close to extinction. Moreover, the identification of Potamogeton taxa with narrow leaves is difficult because of the fewer diagnostic characteristics available for distinction. Thus, in the present study, we conducted morphological and genetic analyses using P. × apertus, collected from Ehime Prefecture, rediscovered after approximately 80 years. The results of genetic analysis indicated that all individuals of the putative hybrid collected from four sites were a unidirectional hybrid between P. oxyphyllus and P. pusillus as maternal and paternal parents, respectively. Morphological analysis demonstrated that P. pusillus, P. × apertus, and P. oxyphyllus had shallow fissure, deep fissure, and non-connate stipules, respectively. Flowers of the hybrid were smaller than those of P. oxyphyllus. In the hybrid, pistils and deformed stigmas were covered by perianths. Leaf and inflorescence morphologies of the hybrid were similar to those of P. pusillus, but the hybrid also had non-elongated inflorescence axes between the upper and lower parts, similar to P. oxyphyllus.

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In Japan, Aristolochia kaempferi Willd. and A. shimadae Hayata (= A. onoei Franch. & Sav. ex Koidz.) are often confused by the identification based on a leaf shape. The leaf morphology of the two species show large variation within an individual and within a species, and the variation is continuous between these species. Due to misidentification of the species, their geographical distribution has been incorrectly grasped. However, the species are clearly distinguished based on a floral morphology. The aims of this paper are to verify the taxonomic history of A. kaempferi group in Japan and to share the correct identification and geographical distribution for A. kaempferi and A. shimadae.

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The pentaploid Pteris × pseudosefuricola (2n = 145), a hybrid between P. cretica (apogamous 3x) and P. multifida (sexual 4x), was newly recorded from Shizuoka and Tochigi Prefectures, Japan. The pinnae are somewhat malformed with irregularly incised margins. The tips of veins in sterile pinnae often reach cartilaginous margins as in P. cretica, but sometimes end short of margins as in P. multifida.

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Orchidaceae, a family of the widespread flowering plants, is reported about 60 species from Shimane prefecture. More than 50% species of Shimane Orchidaceae plants were estimated distributed in Oki islands, an isolated archipelago about 80 km far from Shimane peninsula, and most of them are endangered species. We confirmed the geographical distribution of Orchid Plants in Oki Islands and discuss their conservation status.

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We conducted a preliminary survey of the flora at Mt. Mahiru. Mt. Mahiru (1,059 m alt.) is located in the southern part of the Mahiru Mountains, Tohoku district, Japan, and supposedly harbors a wide diversity of northern plants in Japan, although there has been few studies carried out for the flora. On July 30, 2015, we took a route from Akakura-tozan-guchi to the summit of Mt. Mahiru, and collected plants along the trail and on an alpine meadow around the summit. We collected 98 species of vascular plants, including several species that are rarely seen below 1,300 m alt. in Tohoku district, or below 1,700 m alt. in the central or western part of Honshu. Mt. Mahiru is one of the non-volcanic mountains of heavy snowfall with precipitous valleys in the northern Japan, which suggests that it has kept a suitable condition for montane flora without interruptions by volcanic activities. Further studies on the flora and vegetation of the mountain would provide valuable information on a history of the flora of Japan and on a conservation framework of the biodiversity in Japan.

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Angelica dahurica (Umbelliferae) is distributed in Honshu, Shikoku and Kyushu Islands in Japan, and no recent records from Kanto District in Honshu Isl. Some populations, ca. 300 flowering plants in total, were found growing in the field at Sakura River in Kanto District. Here, we report the discovery of the populations and the results of specimen survey in the herbaria.

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Najas guadalupensis (Sprengel) Magnus subsp. floridana (R. R. Haynes et W. A. Wentz) R. R. Haynes et C. B. Hellquist (Hydrocharitaceae) was recorded from a brackish pond in Ehime Prefecture, Shikoku, as the second locality of the species in Japan. A specimens of the species was proved to have been collected in 1923 from the same area. The origin of the species in Japan was discussed.

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A population of Polygala tatarinowii Regel, an endangered annual herb in Japan, was found near Abukuma Limestone Cave, Tamura City, Fukushima Prefecture, Japan. It could be one of the largest population of the species in Japan, where more than a thousand plants grew on dry meadows beneath limestone bluff or on the flower garden surrounding the Limestone Cave.

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