41 1. Introduction It is widely known that traditional Japanese garden- ing requires moss species as key botanical components for covering natural rocks, wooden and stone walls, tree trunks and sidewalk surfaces. The use of mosses is fre- quently described in the world of Japanese literatures, chiefly in Haiku, as symbolized by a mythical conversa- tion between legendary Haiku poet Basho and Zen master Buccho in which they discuss the Buddhist philosophy on growing green mosses (Suzuki, 1975). In typical Japa- nese gardens, natural rocks partially covered by a layer of thick moss and ponds surrounded by mossy stones repre- sent miniature-sized rocky mountains with forestry slopes and lakes located deep in the forest. These approaches for miniaturizing natural landscapes are well in line with the Buddhist-affected and Shintoist-mixed nature-respecting philosophical preferences in Japan which encourage peo- ple to be surrounded by pieces of nature. In Japan, second to mosses, many Pteridophytes (ferns and fern allies) have also been traditionally used in Japa- nese garden designing. Interestingly, some ground-cover- ing ferns such as members of Selaginellaceae have been considered as mosses by gardening practitioners lacking taxonomical background, largely due to their moss-like appearance (Fig. 1). In place of mossy mats, two Selagi- Pteridophytes as active components in gardening, agricultural and horticultural ecosystems in Japan T. Kawano (*) Laboratory of Chemical Biology and Bioengineering, Faculty and Graduate School of Environmental Engineering, The University of Kitakyushu, Kitakyushu, Japan. Université Paris Diderot, Sorbonne Paris Cité, Paris 7 Interdisciplinary Energy Research Institute (PIERI), Paris, France. Key words: Environment, fern, gardening, insects, Japan, mycorrhizae. Abstract: Many members of Pteridophytes have been traditionally used in the designs of Japanese gardens and a large variety of ferns attract gardeners as greening pieces in the garden designs. However, details or examples of practical uses of ferns in traditional gardening in Japan have only rarely been introduced in non-Japanese literatures to date, despite the importance of ferns in Japanese gardening traditions. In addition to the discussion of ferns in gardening, the use and association of these plants in Japanese agricultural and horticultural sceneries are addressed. The presence and impor- tance of 40 familiar fern species in local gardening, agricultural and horticultural ecosystems are also discussed, as well as the roles of introduced ferns as key elements of ecosystems and their interaction with neighboring biota. Finally, some examples of uses of fern species in environmental science and engineering are also reviewed. Adv. Hort. Sci., 2015 29(1): 41-47 (*) Corresponding author: kawanotom@kitakyu-u.ac.jp Received for publication 22 September 2014 Accepted for publication 24 March 2015 Mini-review Fig. 1 - Living Selaginella remotifolia found in a private garden (Kiyo- take-cho, Miyazaki, Japan). (A) Sheet of growing Selaginella remotifolia covering the ground. (B) Blue-green colored leaflets. 42 Adv. Hort. Sci., 2015 29(1): 41-47 nellaceae members, such as Selaginella remotifolia Spring (Japanese name: Kuramagoke) and Selaginella unicinata (Desv.) Spring (Japanese name: Konterikuramagoke), can be installed in Japanese gardens. Japanese names ending with -goke or -koke are conventionally given to moss spe- cies, despite the fact that these species are taxonomical members of ferns. Furthermore, a large variety of ferns (including stand- ing types) also attract the gardeners as greening pieces in gardening designs. Not only in Japan but also in other East Asian regions such as Taiwan and Korea, some fern species such as Lycopodium fordii Bak. (Lycopodiaceae) are grown as gardening plants and reflect the local flora (Huang et al., 2000). In addition to the Lycopsida members mentioned above (eg. Lycopodium among subclass Aglossopsidae and Se- laginella among subclass Glossopsidae, within the class Lycopsida), Psilotum nudum (L.) P. Beauv. (Psilotaceae; Japanese name: Matsubaran) belonging to the class Psi- lotopsida has long been utilized in Japanese gardening landscapes. Recently it was suggested that this plant com- municates with neighboring plants through a arbuscular mycorrhizal network (Winther and Friedman, 2009). Ac- cordingly, Psilotum nudum, with its non-photosynthetic life cycle, can thrive underground mostly by depending on the transport of photosynthetically fixed carbon from the green plants growing nearby. In the gardens where this plant has been introduced, the micro-ecosystem which al- lows such ecophysiological interspecies communication should be developed. The above fern species have conventionally been con- sidered as members of the phylum Microphyllophyta. As might be expected, other pteridophytes belonging to two other conventional phyla, namely Spherophyta and Pterophyta, are also commonly found in Japanese garden- ing and agricultural landscapes. Despite the importance of Pteridophytes in Japanese gardening traditions, details or examples of practical uses of ferns have only rarely been introduced in non-Japanese literatures to date. As most ferns favor a humid subtropical climate, this article aims to briefly describe and list the Pteridophytes found in the local gardening and agricultural landscapes in the south- western half of Japan. 2. Gardening and Ferns Historically, the inclusion of ferns in gardens has been popular among people of various classes such as farm- ers, warriors, monks and aristocrats, thus ferns were of- ten found in the gardens and backyards of imperial and aristocratic palaces, Shintoist shrines, Buddhist temples, and ordinary houses. Today, it has become much harder to find fern culturing in ordinary houses in the large cities in Japan, yet in rural areas surrounded by semi-wild forests and far from urban areas, the use of ferns can still be found readily. In traditional Japanese gardens, the following fern spe- cies can be found. Matteuccia struthiopteris (L.) Todaro (Athyriaceae; Japanese name: Kusasotetsu also known as Kogomi in the northern Japan) often welcomes the visitor to the gardens. Cyrtomium falcatum (L. fil.) Presl. (Dryopteridaceae; Japanese name: Oniyabusotetsu) and Equisetum hyemale L. (Equisetaceae; Japanese name: Tokusa) are likely planted surrounding ponds and/or wa- terfalls. Beneath the bushes, Polystichum polyblepharum (Roem. Ex Kunze) Presl. (Dryopteridaceae; Japanese name: Inode) can be frequently found. Equisetum hyemale and Dryopteris erythrosora (Eaton) O. Ktze (Dryopteri- daceae; Japanese name: Benishida) can be found in the shade of structures such as a Chashitsu (a tea-ceremony house). Gaps among the rocks or stones can be naturally filled by Cyrtomium falcatum and Pteris multifida Poir (Pteridaceae; Japanese name: Inomotosō). Pteris multifida is a specific host plant that supports the life of caterpillars of a domestic moth of the Noctuidae family, Callopistria japonibia (Fig. 2). Inoue and Sugi (1958) suggested that geographical distribution (size of habitat) of Callopistria japonibia largely depends on the distribution of this fern. This could be a model for studying the contribution of gar- den environments to harbor specific ferns for insect biodi- versity. Moreover, some fern species have been passively but very frequently installed in Japanese gardens, thus their presence strongly reflects the nature of original wild flora. Such species include Pteris cretica L. (Pteridaceae; Japa- nese name: Ōbanoinomotosō), Osumunda japonica Thunb., Botrychium japonicum (Prantl) Underw. (Ophioglossace- ae; Japanese name: Fuyunohanawarabi), Cyrtomium fal- catum, Athyrium niponicum (Mett.) Hance (Athyriaceae; Japanese name: Inuwarabi), Deparia japonica (Thunberg) M. Kato (Woodsiaceae; Japanese name: Shikeshida) (Fig. 3A, D) and Pteridium aqualinum (L.) Kuhn var. latiuscu- lum (Desv.) Underw. Ex Hell (Dennstaedtiaceae; Japanese name: Warabi) (Fig. 3E, F). Fig. 2 - Pteris multifida growing on the stone wall in a private gar- den (Kiyotake-cho, Miyazaki, Japan). (A) Top view of grow- ing plants. (B) Spore-bearing adaxial side of the leaves. (C, D) Plants being fed on by caterpillars of Callopistria japonibia. Arrows indicate the presence of caterpillars. 43 Kawano, Pteridophytes in gardening, agricultural and horticultural ecosystems in Japan Among passively introduced ferns, members of Poly- podiaceae such as Lemmaphyllum microphyllum Pres (Japanese name: Mamezuta), Lepisorus thunbergianus (Kaulf.) Ching (Japanese name: Nokishinobu), and Pyr- rosia lingua (Thunb.) Farw (Japanese name: Hitotsuba) are epiphytic species which are often attached to trees and rocks (Fig. 4). On the surface of rocks and walls, Lem- maphyllum microphyllum is often exposed to competi- tion with higher epiphytic plants such as Ficus pumila L. (Moraceae; Japanese name: Ōitabi). In addition to epiphytic plants, a climbing species, Ly- godium japonicum (Thunb.) Sw. (Lygodiaceae; Japanese name: Kanikusa) is of great interest. Historically, sun- tracking movements associated with a the climbing growth habit were described by Charles Darwin (1875) in two members of Lygodium (L. articulatum and L. scandens). Darwin concluded that “As ferns differ so much in struc- ture from phanerogamic plants, it may be worthwhile here to show that twining ferns do not differ in their habits from other twining plants.” The climbing fern native to Japan, Lygodium japoni- cum, is commonly known as “Japanese climbing fern”. This fern grows very fast and thus often covers nearby liv- ing trees, rocks and walls (Fig. 5). Lygodium japonicum has been exported for ornamental purposes. For instance, this plant was introduced in Florida, USA, in 1932 (Gor- don and Thomas, 1997). 3. Ferns and Japanese people Even before ferns were introduced into man-made gardens, people in Japan traditionally enjoyed going out Fig. 3 - Deparia japonica and Pteridium aqualinum sampled in a pri- vate garden (Kiyotake-cho, Miyazaki, Japan). (A) Adaxial side (top side) and (B) Abaxial side (bottom side) of mature and young bladed of Deparia japonica. (C) Mature and (D) im- mature sporangia on leaflets of Deparia japonica. (E) Living Pteridium aqualinum. (F) Roots and young emerging frond of Pteridium aqualinum. Fig. 4 - Epiphytic ferns found in a countryside private garden (Kiyotake- cho, Miyazaki, Japan). (A) Lepisorus thunbergianus grown on the trunk of a loquat tree (Eriobotrya japonica (Thunb.) Lindl.). (B- D) Lemmaphyllum microphyllum growing on the tree and rocks. Fig. 5 - A climbing fern, Lygodium japonicum, found in a countryside private garden (Kiyotake-cho, Miyazaki, Japan). (A) Climbing growth of Lygodium japonicum on the wooden wall by com- peting with other climbing plants such as Ficus pumila. (B, C) Aggressive growth of Lygodium japonicum winning the compe- tition with other standing plants. (D) Vegetative leaflets. (E, F) Development of sporangia on dorsal side of the leaflets. 44 Adv. Hort. Sci., 2015 29(1): 41-47 to the fields and forests to gather edible young fronds of wild ferns. The relationships between Japanese people and ferns, especially Bracken ferns, are historically, socially and culturally so tight that recreational fern gathering was hardly weakened even among Americans of Japanese ori- gin, as is revealed by the various recipes for cooking ferns found among traditional Japanese communities in the United States (Anderson et al., 2000). Edible wild ferns in Japan include Equisetum arvense L. (Equisetaceae; Japanese name: Sugina), Pteridium aqualinum (popularly known as Warabi), Osumunda japonica Thunb. (Osmun- daceae; Japanese name: Zenmai), and Matteuccia struthi- opteris. Historically, among the Japanese, Equisetum arvense has been used as an herbal medicine with diuretic, antitus- sive, antipyretic, hemostatic, and roundworm-eliminating actions. Therefore, this herbal medicine has been given to patients with gonorrhea, cystitis, edema, bronchitis, and bleeding hemorrhoids (Ikegami, 2013). Furthermore, search for lymphangiogenesis-inhibiting agents in the crude extracts from Equisetum arvense was recently at- tempted (Jeong et al., 2013). Figure 6 shows classical illustrations of rhizome anat- omy of Equisetum arvense L. These illustrations remind us that, like higher plants, ferns, including Equisetum ar- vense, finely develop rhizomes under the soil, suggesting that ferns are one of the key players in the soil ecosystem. Apart from edible and medicinal species, Japanese peo- ple are also familiar with some fern species for ornamen- tal purposes and crafts. The mature fronds of Gleichenia japonica Spr. (Gleicheniaceae; Japanese name: Urajiro) are important for traditional New Year’s decorations. In summer, outside doors or windows of houses, one can find hanging fern-bearing, peat moss-based green balls called “Shinobudama”, which are usually about 10 cm in diam- eter, as one of the favored customs in Japan. A Shinobu- dama literally means a ball of Shinobu which is the Japa- nese common name for Davallia mariesii Moore ex Baker (Davalliaceae). This ornamental arrangement of Shinobu fern is often combined with a wind chime hung outside. Use of Equisetum hyemale L. in traditional craft works should be also noted. The silicate-rich stems of Equisetum hyemale L. have long been used for grinding and honing the surface of wooden table wares and furniture. 4. Agriculturally associated flora of ferns in Japan Paddy fields for culturing rice plants (Oryza sativa L.) are man-made wetlands which cover about 50% of the agricultural land in Japan. Some fern allies bloom out in the paddy field after the harvest of rice. Typical examples of dominating aquatic and semi-aquatic ferns in the post- rice paddy include Ceratopteris thalictroides (L.) Brongn. (Adiantaceae; Japanese name: Mizuwarabi), Salvinia na- tans (L.) All (Salviniaceae; Japanese name: Sanshōmo), Azolla japonica Fr. et Sav. (Azollaceae; Japanese name: Ōakaukikusa), Azolla imbricata (Roxb.) Nakai (Azolla- ceae; Japanese name: Akaukikusa), and Marsilea quadri- folia L. (Marsileaceae; Japanese name: Denjisō). Marsilea quadrifolia is most likely to be very sensitive to rice field herbicides and thus this plant species is rarely found nowa- days (Luo and Ikeda, 2007). Fig. 6 - Anatomical illustrations of underground structures of Equisetum arvense L. found in a classical book by J. Duval-Jouve (1864). (A) Horizontal rhizomes. (B) Vertical rhizomes. (C) Section of large tuber attached to rhizome. (D) Cells of a tuber with starch granules (left) and vessel (right). (E, F) Starch granules. This book was originally collected and preserved through collabora- tive research between Université Paris Diderot and The Univer- sity of Kitakyushu (Kawano and Bouteau, 2007; Kawano et al., 2008). Original images were digitally scanned and slightly modified (illustrations of other plant species were masked). 45 Kawano, Pteridophytes in gardening, agricultural and horticultural ecosystems in Japan 5. Breeding for horticultural purposes Some Pteridophytes have been positively subjected to breeding efforts, especially during the era of Tokugawa Japan known as the Edo period (1603-1868). Among the ferns listed in this section, the breeding history for Psilo- tum nudum (known as Matsubaran) is estimated to have a long history and thus a number of varieties are available (Murata and Yashiro, 2006). Also some ornamental spe- cies with attractive leaf orientation, such as Onychium ja- ponicum (L.) (Thunb.) Kunze (Parkeriaceae/Adiantaceae; Japanese name: Tachishinobu) and Nephrolepis cordifolia (L.) Presl (Lomariopsidaceae; Japanese name: Tamashida) are popularly bred and cultivated for both garden use and for ornamental pots. Note that, nowadays, Nephrolepis cordifolia often requires protection under a glass house especially during the winter season. Some fern species are also favored by gardeners and plant growers and are nowadays bred and available on the market. Such ferns considered as gardening plants include Selaginella unicinata (Fig. 1), Selaginella tamariscina (Beauv.) Spring (Selaginellaceae; Japanese name: Iwahi- ba), Selaginella involvens (Sw.) Spring (Selaginellaceae; Japanese name: Katahiba), Adiantum capillus-veneris L. (Adiantaceae; Japanese name: Hōraishida), Sphenomeris chinensis (L.) Maxon. (Lindsaeaceae; Japanese name: Horashinobu), Pteris nipponica W. C. Shieh (Pteridaceae; Japanese name: Matsuzakashida) and Asplenium antiqu- um Makino (Aspleniaceae; Japanese name: Ōtaniwatari; this plant often requires green house or similar facilities). Selaginella unicinata is believed to have been brought from southern regions in China several centuries ago. Adiantum capillus-veneris is naturally found in the western half of Ja- pan, but there are still some discussions on the origins of this fern (Murata and Yashiro, 2006). Among Adiantum spe- cies, Adiantum monochlamys Eaton (Adiantaceae; Japanese name: Hakoneshida) is hardly cultivated in gardens (Murata and Yashiro, 2006). Among the varieties of Pteris nipponica, lines or individuals with white spots on the leaves are likely favored on the market (Murata and Yashiro, 2006). It should be noted that even today, many efforts to develop and/or in- troduce new horticultural fern varieties of East Asian origin are being made (Xu et al., 2006). 6. Uses of ferns in environmental science and engineering Unlike mosses, Pteridophytes possess a highly devel- oped root system (rhisomes) by which minerals and metals are effectively taken up by growing plants. From an envi- ronmental point of view, some ferns are receiving more at- tention than ever, after pioneering works by Japanese fern specialists, since some ferns might be useful indicators and/or tools to assess and remediate contaminated soils. Most metallic ions present at high concentrations are toxic to living plants by targeting and damaging the root cells exposed to the soil (Kawano et al., 2005). Athyrium yokoscense (Fr. Rt Sav.) Christ (Athyriaceae; Japanese name: Hebinonegoza), indigenous to East and North East Asia including Japan and Korea, is known to thrive in and around the sites of mining by rooting in soils contaminat- ed with high concentrations of heavy metals (such as Zn, Cd, Pb, and Cu) and As (Morishita and Boratynski, 1992; Van et al., 2006). Therefore, the presence or distribution of this plant strongly indicates the history of the soil use or contaminations (Morishita and Boratynski, 1992). It has been well documented that Athyrium yokoscense not only tolerates but also effectively takes up the contaminating elements from the surrounding environments, as examined both at cellular level (Yoshihara et al., 2005) and field- grown plant level (Morishita and Boratynski, 1992; Kama- chi et al., 2005). Similar approaches are now being attempted with re- gard to other fern species. Use of a hyper-accumulator fern for arsenic and metals, Pteris vittata L. (Pteridaceae; Japa- nese name: Moejimashida) is one successful example of fern-based phytoremediation of metal-contaminated and arsenic-poisoned soils (An et al., 2006; Xie et al., 2009). Interestingly, a recent proteomic approach by Bona et al. (2011) suggested that the hyper-accumulating nature of Pteris vittata requires the presence of symbiotically formed arbuscular mycorrhizae. Furthermore, unpub- lished results presented by Chien et al. (2012) during an oral presentation at the 64th annual meeting of the Soci- ety for Bioscience and Bioengineering, Japan, suggested a possible relationship between the mechanism of arsenic accumulation by Pteris vittata L. and bacterial flora in the rhizosphere. These studies consistently support the view that composition of the micro-flora in the soil inevitably affects the environmental responses performed by rhi- zome-developed fern species. 7. Preservation of ferns and related flora and fauna in the gardens Based on statistical techniques, namely two-way indi- cator species analysis (TWINSPAN) and Detrended Cor- respondence Analysis (DCA), Murakami et al. (2003) re- ported that there is a relationship between micro-landforms and the fern species composition in forest islands. This is the case of surveys on the ecological status of fragmented forests within the urbanized area of Kyoto city since fern members are largely considered to form a group of envi- ronmental indicators in the urban matrix. The authors con- cluded that the difference in species composition of ferns was shown to reflect differences in micro-landforms. For example, Polystichum polyblepharum and many other spe- cies are favored in valley bottoms in the small forest is- lands while some species such as Dryopteris erythrosora and Gleichenia japonica are favored on the slopes. Japanese gardens can be considered as a local ecosys- tem that allows semi-wild propagation of fern species. This is largely due to the diversified micro-landforms in 46 Adv. Hort. Sci., 2015 29(1): 41-47 Japanese garden designs which allocate rocks, mounds, valleys, falls and ponds within small areas. Indeed, Japa- nese gardens can be considered models for botanical dis- play and/or preservation of semi-wild fern species and in- teracting flora, fauna and microbiota. 8. Conclusions In this article, the use and associations of ferns in Japa- nese agricultural and horticultural sceneries are reviewed and discussed. Through listing 40 key Japanese fern spe- cies in gardening, horticulture and environmental studies in Japan, the author has shown that these ferns behave as key building blocks for the semi-wild and half man-made local ecosystems in gardens and agricultural fields. The author has also noted that these ferns are highly and ac- tively communicating and competing with other organ- isms such as weeds, trees and insects, and also cope with environmental stress through rhizomes. Human-fern inter- action may be one such interspecies communication. 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