Carex livida (Wahlenb.) Willd. (livid sedge), a perennial herb of Cyperaceae, is considered a relict species from the glacial period and designated as a rare species in the Japanese red list. We investigated the vegetation and the environmental conditions of mires near Lake Rausu in Hokkaido in order to understand the phytogeographical and habitat characteristics of the species. We also compared recent vegetation of the study area with those investigated in the 1980s, and examined whether environmental changes in the mire had affected its vegetation. The vegetation analysis classified the study areas into two hummock communities (R1 and R2) and one hollow community (R3). Carex livida mainly occurred in the communities R2 and R3. Less changes of the vegetation since 1980s was detected. Compared with the vegetation of mountain and lowland mires in Japan, the hummock communities (R1 and R2) corresponded to the bog vegetation (Moliniopsio-Sphagnion papillosi Tx., Miyawaki et K. Fujiwara 1970). The community R3 resembled hollow vegetation (Scheuchzerietea palustris Den Held, Barkman et Westhoff, em. Tx., H. Suzuki et K. Fujiwara 1970) and small-herb communities of oligotrophic wetlands (Eriocaulo-Rhynchosporion K. Fujiwara 1979). However, the character species and differential species of each class and alliance did not occur characteristically. Microtopography, characterized by kermis and strings alternately arranged parallel to the contour lines of the sloping mire (called the 'Kermi-Schlenke complex'), was observed in the study area, suggesting that C. livida grows in and around hollows in mires with this patterned topography.

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It is known that paddy fields in Japan share plant species with those in tropical Asia. Few studies, however, have analyzed the floristic composition of paddy fields in tropical Asia. In this study, the floristic composition of some tropical Asian paddy fields, located on Hainan Island, China, were analyzed using phytosociological methods. As a result, following vegetation units were recognized: A) Monochoria vaginalis var. plantaginea-Ludwigia adscendens community with Eriocaulon sieboldianum lower unit, Blyxa japonica lower unit and Cyperus iria lower unit; and B) Cyperus brevifolius-Ageratum conyzoides community with Cyperus pilosus lower unit and Fimbristylis miliacea lower unit. Further, the floristic compositions of paddy fields in Hainan and Japan were compared, and Hainan Island and Japan shared many species including the species of Sagittario-Monochorietum Miyawaki 1960 and its upper units. In fallow paddy fields and on ridges in Hainan Island, the species of Lindernion procumbentis Miyawaki et Okuda 1972 and Bidentetea tripartitae Tx., Lohm. et Prsg. 1950 occurred, while these species grow in paddy fields or along the streams in Japan from summer to autumn. The species of Alopecurion amurensis Miyawaki et Okuda 1972 and Agropyro kamoji-Rumicion japonici Miyawaki et Okuda 1972 that grow in dried paddy fields or on the ridges in Japan from autumn to spring, were not found in paddy fields or on ridges in Hainan Island.

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It is known that deciduous broad-leaved forests in the subtropical to warm temperate zones in Japan are dominated by pioneer trees such as Mallotus japonicus and Zanthoxylum ailanthoides. These deciduous broad-leaved forests are classified as Fico-Mallotalia S. Suzuki et Miyawaki 1986 based on species composition. A new association within the warm temperate deciduous forest of Fico-Mallotalia, Senecioni scandentis-Celtidetum sinensis was described on steep slopes along coastal areas of southern Shikoku. Melio azedarach-Evodietum meliifoliae Nakamura 1982 of Fico-Mallotalia, was already described along other coastal areas of southern Shikoku. As a result of comparison of species composition of Fico-Mallotalia on the Japanese mainland, Senecioni scandentis-Celtidetum sinensis has evident floristic differences on the presence of character species as like Swida macrophylla and Senecio scandens, Stephanotis mucronata. Senecioni scandentis-Celtidetum sinensis also shows evident floristic differences with neighboring evergreen broad-leaved forests, because that has character species of Clerodendro-Mallotion japonicae Ohba 1970 and the other species as like Rubus sieboldii and Actinidia rufa, Stephania japonica. Although the vegetation units of Fico-Mallotalia are mainly pioneer communities, Senecioni scandentis-Celtidetum sinensis is regarded as a permanent community because of their unstable habitat and its distinct layered structures. The distribution of Senecioni scandentis-Celtidetum sinensis is limited on the coastal part of central and western areas of Tosa Bay, Shikoku, below altitude 150m.

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The distribution and ecology of Carex matsumurae Franch. (Cyperaceae) were studied in Japan. The distribution area of this species was from the northern Ryukyu Islands through Kyushu and Shikoku to the Hokuriku district on the Sea of Japan side and to the Izu Islands on the Pacific side. More than 50% of the localities were on islets with areas of less than 1km^2 and the species can be considered to be an islet-biased plant. This species grew on the forest floor in the Persea thunbergii type of lucidophyllous forest, which is distributed in the coastal areas of warm-temperate zones. The young plants and the seedlings of this species were mostly found at bare micro-site in the forest developed on a slope, but not at litter-deposited site in the forest developed on a flat plane. The current distribution can be explained by the fact that most of the natural forests in the coastal area of warm-temperate zones were destroyed and C. matsumurae was extinct in many places on large islands and mainland.

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