The question of how many vascular plant species occur in whole Korean peninsula and its adjacent islands might be answered based on prominent literature resources, such as ‘Lineamenta Florae Koreae’ (Lee 1996), which lists 4,071 taxa, whereas ‘A Synonymic List of Vascular Plants in Korea’ (Korea National Arboretum and the Plant Taxonomic Society of Korea 2007) reports 4,881 taxa that include both naturalized and cultivated plants. However, it is more difficult to determine how many wetland vascular plant species inhabit or to decide which of them are wetland species truly.

The range of wetland species covers a wide spectrum of habitats associated with water. Obligate wetland species, which live continuously in the water, are one extreme while obligate upland species, found in forests or dry meadows, are at the other end of the spectrum. Because numerous species have become established between those two extremes, the practice of categorizing plants according to water conditions is artificial and may not always be precise. However, categorized information is necessary if we are to preserve, restore, and use those species as part of our wetland management schemes.

We previously assigned all 4,050 wetland taxa on the Korean Peninsula and its adjacent islands to several groups (Choung et al. 2012). Our most important exercise was to classify those vascular plants into five categories based on their frequency of occurrence in wetlands. To do so, we applied criteria slightly modified from those of the US Fish and Wildlife Service (1997). The following definitions were used:

For our list, we defined ‘wetland’ broadly, according to the Ramsar Convention (1971), i.e., “wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters”. Such sites would necessarily include most rivers, streams, lakes, reservoirs, tidal flats, beaches, rice paddies, and fish farms.

The categories of obligate and facultative wetland plants were further divided, based on degree of wetness, into hygrophytes and aquatic macrophytes. The latter were then subdivided into four types according to morphology. In addition, major habitat, growth form, longevity, leaf form, and seasonality were recorded for each species. Decisions pertaining to the categorization of each species were made in our group discussions, which also referenced the literature and field experience. Here, we report the status of wetland plant species in Korea as a follow-up analysis of our earlier listings.

Based on our categorized species list of 4,050 taxa, including 3,769 native and 281 naturalized taxa (Choung et al. 2012), we have now summarized the distribution of wetland plants on the Korean Peninsula and its adjacent islands. The definitions and descriptions of all terms used here are referenced in that earlier list in detail.

Among the 4,050 plant taxa, 240 (6%) and 239 (6%) are considered as OBWs and FACWs, respectively (Table 1). These 479 wetland taxa account for 12% of the total. In contrast, upland species, such as OBUs and FACUs, comprise 84% of all taxa considered here. This indicates that terrestrial ecosystems are well developed when compared with wetlands. Topographically, the inland wetlands are less developed because, historically, they have not been as strongly influenced by glaciers or activity by earthquake, volcanos, faults, and folds in that region (Wikipedia, Korea 2015). However, the coastal wetlands cover long stretches of beaches and mudflats. Therefore, to prevent flooding and secure those water resources, numerous artificial dams and reservoirs have been constructed in areas that support habitats for wetland plants.

Within our subdivisions of aquatic macrophytes and hygrophytes, the former includes 69% of all OBWs and FACWs while the latter accounts for 31% of the total (Fig. 1). Whereas all FACWs are hygrophytes, the OBW category consists of both aquatic macrophytes and hygrophytes. Among those macrophytes, approximately half (46%) are of the emergent type while the smallest portion (10%) contains species that are of the floating type.

As expected, most of the OBWs (62%) inhabit aquatic environments while the rest live in wet meadows, e.g., riparian and littoral zones that are saturated with water throughout much of the year (Table 2). However, no standing water is present except for brief to moderate periods during the growing season. Compared with OBWs, 90% of FACW plants grow in wet meadows while 10% exist in damp forests. Members of the genus Salix are representative of that forest category.

Overall, 77% of the Korean taxa are herbaceous while the rest are woody plants (Table 3). All members of OBWs are herbaceous but most woody plants belong to either the OBU or FACU category. Because of prolonged, harsh winter conditions, 92% of all taxa are green only in the summer (Table 4) and just two OBW taxa, Potamogeton oxyphyllus and Lycopodium cernuum, are evergreen.

We believe that the information gleaned from our study will be useful for developing strategies aimed at preserving and restoring wetlands and their resident plant species. Moreover, our data will provide a foundation when devising plans to assess the health of Korean wetland ecosystems as well as to create artificial wetlands there.