Japanese red maple (Acer pycnanthum K. Koch; Japanese common name, Hananoki) is an endangered, indigenous species that grows only in discrete wetlands in central Honshu, Japan (Ogata, 1965a; 1965b; Barnes et al., 2004). It is listed as “vulnerable”: the possibility of extinction is increasing (Ministry of Environment, 2007). Its natural distribution is restricted to a geographic area of only 1,090 km² (Barnes et al., 2004), and serious habitat deterioration has been reported (A Survey Group on Dynamics of Japanese Flora, 1989; Japanese Red Maple Conservation Group, 2003).

Japanese red maple is a relic species of geologic time. Ancestral fossil species, Acer tricuspidatum Bronn and Acer tigilense Chelebaeva, were widely distributed in the Northern Hemisphere in Miocene time (Walther, 1972; Tanai, 1983; Wolfe and Tanai, 1987). European populations became extinct in the early Pliocene due to climatic deterioration (Tanai, 2001), and today red maple species only occur in central Japan and eastern North America (van Gelderen et al., 1994). One is known as Japanese red maple (Acer pycnanthum), and the other is red or swamp maple (Acer rubrum L.). The divergence time of these species was estimated at about eight million years (Hasebe et al., 1998). Morphologically, A. pycnanthum and A. rubrum are nearly indistinguishable (van Gelderen et al., 1994), the difference being mainly in leaf lobing and other leaf characteristics. Hybridization between these species produced viable seed, and vigorous seedlings were verified as interspecific hybrids (Shimizu and Uchida, 1993). Both species grow in wetlands such as palustrine and riverine swamps (Hirabayashi and Takahashi, 1969; Gleason and Cronquist, 1991; Barnes et al., 2004).

Although the two maples are similar in most characteristics, the extent of their respective geographic distribution is remarkably different. Acer rubrum is among the most widely distributed and abundant tree species in eastern North America (Walters and Yawney, 1990) and dramatically invading forests dominated by oaks and pines (Abrams, 1998), whereas Acer pycnanthum occurs only in a very limited geographic range in central Japan (Barnes et al., 2004). Because of the marked contrast with A. rubrum, i.e., similarity in morphology and dissimilarity in geographic distribution, A. pycnanthum has attracted considerable attention by botanists (Ogata, 1965b).

In addition, Japanese red maple is deeply associated with local Japanese culture. Large trees, occasionally >30 m tall, and their wide-spreading crowns exhibit brilliant red flowers in spring and beautiful reddish-orange foliation in fall. Many large trees, even single isolated trees, have been designated as "natural monuments" by national and local governments to respect its rarity and scientific importance (Miyoshi, 1925; 1926; Hanai et al., 2003). Large trees are often preserved at shrines and temples near natural populations. In 1835, the large gate of Tennyuuji Temple in Gifu prefecture was constructed with the wood from Japanese red maple growing near the temple (Miyoshi, 1926). Ena high school, located at a center of its natural distribution, and two other schools have adopted Japanese red maple as their symbol. In 1911, a seedling of Japanese red maple was presented to the prince of Japan (Miyoshi, 1926) because he showed great interest in Japanese red maple during his visit to Shiga prefecture (Nomura, 1914) where a large individual still grows at the Hachiman shrine. There are many interesting stories demonstrating that Japanese red maple has received great public attention.

Research of Japanese red maple in early time was summarized by Ogata (1965b). According to Ogata, Japanese red maple was first described by Iinuma (unpublished, in Makino, 1902) and Ito (1873) in the late 19th century. Earlier than Ito’s publication, the scientific name Acer pycnanthum was given by Koch based on the plant specimen sent to him from Ito (Koch, 1864). Koch described Japanese red maple as being very similar to red maple (i.e., A. rubrum), but he differentiated the two species by leaf, flower bud, and twig morphology (Koch, 1864). However, in 1902, Makino insisted that A. pycnanthum should be the same species as A. rubrum because he suspected that in the past red maple had been introduced into Japan from North America (Makino, 1902). Thus, Makino renamed the species Acer rubrum Linn.

Ten years after the Makino’s proposed correction, a natural population of Japanese red maple was first discovered at Sakamoto town in Ena gun, which is located today in Nakatsugawa city, Gifu prefecture (Koidzumi, 1912). Because of this discovery, Makino regarded Japanese red maple as different taxon from A. rubrum, but he considered it as a variety of A. rubrum, i.e., A. rubrum var. pycnanthum Makino (Makino, 1912). This synonym had been used at least until 1970s (e.g., Kurata, 1973), but A. pycnanthum is widely used today.

After the discovery of the Sakamoto population, new populations were located one after another in Nagano, Gifu, and Aichi prefectures (Ogata, 1965b). The most northern isolated locality, Iyari, was reported later by Yokouchi (1962). Populations in Shiga prefecture, which are widely known to the public, are considered to be of planted origin (Miyoshi, 1925; Ogata, 1965b).

Ogata (1965a) published a comprehensive report on the geographic distribution and systematics of Japanese red maple. He listed the known populations at that time based on the work by Hama (1921, in Ogata, 1965a) and summarized that they were mainly concentrated in the southeastern part of Gifu prefecture and the southern part of Nagano prefecture. He also described the morphological and taxonomical characteristics of the species (Ogata, 1965a; 1967).

Japanese red maple has been regarded as a member of special endemic flora around Tokai region (Ueda, 1989; 1994; 2002). According to Ueda’s reviews (1989; 1994), Koidzumi (1934) first referred to Japanese red maple as a characteristic plant species around Mikawa highland region, central Japan. Sugimoto (1958) also referred to Japanese red maple as an example of species characterizing the flora around Ise Bay. After that, Inami (1966) introduced the term “circum-Ise Bay element” for the species whose main distribution is located in Mie, Gifu, Aichi, and Shizuoka prefectures. Japanese red maple was included in this species group (Kikuchi et al., 1991). Furthermore, Ueda (1989) defined 13 species of the circum-Ise Bay elements as “Tokai hilly land elements” that rely on small peatless mires in Tokai region, including Japanese red maple.

The endangered status of Japanese red maple was reported in the first national Red Data Book (A Survey Group on Dynamics of Japanese Flora, 1989). Japanese red maple was designated a “vulnerable” species, and major reasons of the decline were considered as development of residential area and golf courses. The endangered status did not change in the revised Red Lists (Environment Agency of Japan, 2000; Ministry of Environment 2007). Also, Japanese red maple is listed as a prefectural endangered species in all the three prefectures, Nagano, Gifu, and Aichi, where its natural geographic distribution is located (A Survey Group on Dynamics of Japanese Flora, 1989). In 2005, Japanese red maple communities in southern Nagano prefecture were designated “endangered plant communities of Nagano” (Nagano Biodiversity Research Group et al., 2005). A local conservation group, “Japanese red maple conservation group,” effectively works for conservation of the species and its wetland habitats.

	Acer pycnanthum April. Iida, Nagano, Japan
	Acer pycnanthum November. Iida, Nagano, Japan
	Acer pycnanthum November. Iida, Nagano
	Acer pycnanthum November. Iida, Nagano, Japan
	Acer pycnanthum April. Ena, Gifu, Japan
	Acer pycnanthum April. Ena, Gifu, Japan
	Acer pycnanthum November. Achi, Nagano, Japan
	Acer pycnanthum and wetland August. Toki, Gifu, Japan
	Acer pycnanthum forest May, Nakatsugawa, Gifu, Japan
	Acer pycnanthum April. Mizunami, Gifu, Japan）
	Acer pycnanthum April. Ena, Gifu, Japan
	Acer pycnanthum forest May. Nakatsugawa, Gifu, Japan
	Acer pycnanthum & Veratrum stamineum var. micranthum May. Achi, Nagano, Japan
	Acer pycnanthum April. Toki, Gifu, Japan
	Acer pycnanthum November. Iida, Nagano, Japan）
	Acer pycnanthum

Red maple (Acer rubrum)

Red maple (Acer rubrum L.) is the most widely distributed and abundant deciduous tree species in eastern North America (Walters & Yawney, 1990). Its range spans c. 24_ of latitude, 40_ of longitude and from sea level to 1370 m elevation (Sargent, 1922; Walters & Yawney, 1990). It occurs on virtually every type of glaciated and non-glaciated landform within its range, from excessively drained to very poorly drained soils, and on sites of both high and very low nutrient availability (Barnes & Wagner, 2004). Rarely found in pure stands, red maple occurs in 56 of the 88 non-tropical forest cover types of the eastern USA (Eyre, 1980). Numerous studies have demonstrated great genetic and phenotypic variation among and within populations, as well as clinal variation in ecological traits such as phenology and growth related to day length, length of growing season, temperature and preference for wet versus dry sites (Perry & Wang, 1960; Townsend et al., 1982; Farmer, 1997; Bauerle et al., 2003). In their description of A. rubrum L., Gleason & Cronquist (1991, p. 353) conclude: ‘Morphologically, cytologically and ecologically variable, but indivisible’. There are currently three broadly accepted geographic varieties: A. rubrum var. rubrum Sarg., A. rubrum var. drummondii Sarg. and A. rubrum var. tridens Wood. Reference & More information: Saeki, I., C. W. Dick, B. V. Barnes, and N. Murakami. Comparative phylogeography of red maple (Acer rubrum L.) and silver maple (A. saccharinum L.): impact of introgression, habitat preference, and glacial history in sister species. Journal of Biogeography (in press)   Acer rubrum var. rubrum July. Michigan, USA.   Acer rubrum var. rubrum July. Ontario, Canada   Acer rubrum var. drummondii June. Illinois, USA   Acer rubrum var. tridens April. Georgia, USA   Acer rubrum var. tridens April. Florida, USA.   Acer rubrum var. tridens April. Florida, USA.   Acer rubrum var. tridens April. Florida, USA.   Acer rubrum var. rubrum July. Michigan, USA.   Acer rubrum var. rubrum July. Michigan, USA.   Acer rubrum var. rubrum July. Ontario, Canada.   Acer rubrum var. rubrum July. Ontario, Canada.   Acer rubrum var. rubrum July. Ontario, Canada.   Acer rubrum var. tridens April. Georgia, USA  　Silver maple　(Acer saccharinum)

Silver maple (Acer saccharinum L.) is also widely distributed in eastern North America but does not reach the latitudinal extremes of A. rubrum or the extent of its occurrence west of the Mississippi River. It is markedly site differentiated from A. rubrum, occurring in full sun along the bank and adjacent terrace (first bottom) of river floodplains that are inundated during the first part of the growing season, and in microsites of very poorly drained swamps and ice-block depressions. In the latter ecosystems, the two species may grow side by side. Despite ecological and cytological barriers to hybridization, natural hybrids have been reported in herbarium collections (A. freemanii E. Murray) (Ellis, 1963) and controlled crosses have been made to produce horticultural varieties, such as the Freeman maple (Freeman, 1941; Murray, 1969; Santamour, 1993). Ten intra-specific subspecies, varieties and forms (excluding horticultural cultivated varieties) have been recognized (Index Kewensis, Gray Card Index), and are based on minor differences in leaf morphology. No geographic taxa have been recognized. Reference & More information: Saeki, I., C. W. Dick, B. V. Barnes, and N. Murakami. Comparative phylogeography of red maple (Acer rubrum L.) and silver maple (A. saccharinum L.): impact of introgression, habitat preference, and glacial history in sister species. Journal of Biogeography (in press)   Acer saccharinum July. Michigan, USA.   Acer saccharinum July. Michigan, USA.   Acer saccharinum June. Illinois, USA.   Acer saccharinum June. Illinois, USA.   Acer saccharinum June. Illinois, USA.   Acer saccharinum June. Illinois, USA.   Acer saccharinum June. Illinois, USA.  　Others

	Magnolia stellata: Assoicated species of Acer pycnanthum
	Magnolia stellata: Assoicated species of Acer pycnanthum
	Chionanthus retusus Rare tree whose distribution is similar to Acer pycnanthum
	Chionanthus retusus Rare tree whose distribution is similar to Acer pycnanthum
	Chionanthus retusus Rare tree whose distribution is similar to Acer pycnanthum
	Clematis patens Associated species of Acer pycnanthum
	Habenaria radiata Rare species which sometimes grow together with Acer pycnanthum
	Heloniopsis orientalis Associated species of Acer pycnanthum
	Acer miyabi var. shibatae  Endangered maple in Japan
	Babies of Raccoon dog found in Acer pycnanthum forest.
	Japanese tree frog found in Acer pycnanthum forest.
	Turtles in Acer rubrum site.
	Satoyama forest in Spring. Ena, Gifu, Japan.