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(American Journal of Botany. 2002;89:1779-1784.)
© 2002 Botanical Society of America, Inc.

Reproductive Biology

Ecophysiology of seed germination in Erythronium japonicum (Liliaceae) with underdeveloped embryos1

Tetsuya Kondo2,4, Nori Okubo2, Taku Miura2, Kazushige Honda3 and Yukio Ishikawa3

2Graduate School of Agriculture, Hokkaido University, Kita-ku, Sapporo 060-8589, Japan; 3Department of Forestry and Landscape Architecture, Hokkaido College, Senshu University, Bibai 079-0197, Japan

Received for publication January 25, 2002. Accepted for publication May 16, 2002.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Erythronium japonicum (Liliaceae) (Japanese name, katakuri) is indigenous to Japan and adjacent Far East regions. We examined their embryo elongation, germination, and seedling emergence in relationship to the temperature. In incubators, seeds did not germinate at 20°/10° (light 12 h/dark 12 h alternating temperature), 20°, 15°, 5°, or 0°C with a 12-h light photoperiod for 200 d. They germinated at 15°/5° or 10°C, starting on day 135. If seeds were kept at 20° or at 25°/15°C before being exposed to 5°C, the seeds germinated, but if kept at 25° or 30°C they did not. Embryos at 25°/15°C grew to half the seed length without germinating; at 0° or 5°C, embryos elongated little. Embryos grew and seeds germinated when kept at 25°/15°C for 90 d and then at 5°C. In the field, seeds are dispersed in mid-June in Hokkaido and in Honshu, mid-May to mid-June. Seeds do not germinate immediately after dispersal because the embryo is underdeveloped. Embryos elongated at medium temperatures in autumn after summer heat, and germination ends in November at 8°/0°C. After germination, seedling emergence was delayed, and most seedlings were observed in early April around the snowmelt when soil cover was 2–3 mm.

Key Words: ecophysiology • embryo elongation • Erythronium japonicum • seed germination • seedling emergence • temperature


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Erythronium japonicum Decne. (Liliaceae) (Japanese name, katakuri) is a typical vernal plant that inhabits the cool-temperate mesic deciduous-forest floor. Erythronium japonicum is distributed throughout Hokkaido and in broad areas from the lowlands to the montane zone in northern and central Honshu, especially in the Japan Sea side of Honshu, Japan. It also occurs sporadically on the montane zone of southwestern Honshu, Shikoku, and Kyushu in Japan. It is distributed also in Korea, northeast China, Sakhalin, and the Kurile Islands (Ohwi, 1983 ). In Hokkaido, after the long winter with deep snow, spring is ushered in by many flowers immediately after the snow melts. These spring ephemerals include Adonis amurensis Regel et Radd, Anemone raddeana Regel, Corydalis ambigua Cham. et Schl., Trillium camtschatcense Ker Gawler, and E. japonicum. Their flowering and seed setting occur in early spring and mid-June, respectively, and their growth ends in early summer. There are many popular scenic locations of these indigenous populations, including large-scale vistas of flowers in Japan.

Erythronium japonicum has been studied in terms of its life cycle, size-class structure, resource allocation (Kawano, Hiratsuka, and Hayashi, 1982 ), breeding and pollination systems (Kawano and Nagai, 1982 ), seed dispersal (Kawano, Hiratsuka, and Hayashi, 1982 ; Ohkawara, Higashi, and Ohara, 1996 ), dry-matter production, environmental requirements (Sawada et al., 1997 ), growth and reproduction as examined by a mathematical model (Yokoi, 1976 ), and population structures and dynamics (Yokoi, 1976 ; Sawada et al., 1997 ; Takada, Nakayama, and Kawano, 1998 ). However, germination information needed for propagation and maintenance of population numbers has not been reported. We examined the germination ecology and temperature requirements for germination under both outdoors and laboratory conditions.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
Seed collection
Seeds used in this study were collected from a natural population in a deciduous woodland in Asahikawa City, Hokkaido, Japan (43°52' N, 142°27' E). Light-brown fruits were collected in paper bags on 8 June 1998 and 16 June 1999 when some individuals in the population had already dispersed seed. Collected fruits were brought to our laboratory, placed in stainless steel trays, and left to dry for 1 wk. Most of the fruits had dehisced within this time. The seeds were threshed from the dried fruit by hand, and were then winnowed, put into paper envelopes, and stored in a plastic container with silica gel at 5°C until the start of the experiment.

Phenology of embryo growth in the outdoor pot experiments
Seeds collected in 1999 were used. Ten seeds were cut into thin sections with a microtome, and the maximum embryo length of each seed was measured under a dissecting microscope equipped with a micrometer on 25 June 1999. On the same day, 30 seeds were put into a fine-mesh polyester bag, and five such bags were buried in leaf mold in a nursery flat at the depth of 3 cm. The flat was put in a steel-framed greenhouse without vinyl or other covering at Hokkaido University in Sapporo (43°04' N, 141°20' E), and the greenhouse was covered with shade cloth to simulate the light conditions of a forest floor. The leaf mold was kept moist throughout the experiment. The shade cloth was removed, and the flat was kept covered with a straw mat from 15 November 1999 through 18 April 2000. Snow first fell in mid-November and covered the ground from the end of November to the end of March. On 26 July, 25 August, 23 September, 22 October, and 21 November 1999, a bag was taken from the mold and embryos of ten seeds were measured as above. All but three of the seeds had germinated by 21 November, so on this day, only three embryos were measured. The temperature of the soil surface above the bag was measured every 15 min with an electric thermograph throughout the experiment. The daily mean, maximum, and minimum temperatures were calculated.

Phenology of germination in the outdoor pot experiments
Seeds collected in 1999 were used. One hundred seeds were put in a fine-mesh polyester bag and three such bags were buried in leaf mold in a nursery flat at the depth of 3 cm on 25 June 1999. The flat was placed in the steel-framed greenhouse and treated as in the experiment on embryo growth.

The three bags were lifted, and seeds were examined for germination every month from June 1999 to January 2000. Here, germination is distinguished from emergence of seedlings. Germination was said to have occurred when the radicle emerged from the seed, and seedlings were said to have emerged when a cotyledon appeared above the ground. Germinated seeds were removed from the bags, which were buried again. In winter, the flat was dug out from snow for examination of germination. The maximum snow cover was about 1.5 m. The temperature of the soil surface was measured as above.

Phenology of seedling emergence in the outdoor pot experiments
Seeds collected in 1998 were used. Three pots 19 cm in diameter were filled with a 1 : 1 mixture of peat moss and vermiculite. One hundred seeds were sown in each pot and covered with 2–3 mm of sieved soil on 16 June 1998. The pots were covered with shade cloth to prevent dryness and protect against insects and placed in the greenhouse. The soil was kept moist throughout the experiment. The shade cloth was removed and the pots were covered with a straw mat from 16 October 1998 until 19 April 1999. Pots were examined monthly for seedlings that had emerged, and emerged seedlings were removed from the pots. The maximum snow cover was about 1.5 m. The temperature of the soil surface was measured as above.

Effects of constant or alternating temperatures on germination
Seeds collected in 1999 were treated with 500 ppm (parts per million) of benomyl for 24 h for bacterial control before being used in this experiment. On 24 June 1999, the experiment was started in a temperature- and light-controlled incubator with a 12-h photoperiod with seeds in 9-cm glass petri dishes on a double layer of filter paper moistened with distilled water. Five constant temperatures (0°, 5°, 10°, 15°, and 20°C) and two regimes of alternating temperatures with 12 h at each temperature (15°/5° and 20°/10°C, light 12 h/dark 12 h) were used. At constant temperatures, seeds were exposed to light for 12 h each day; and at 12/12 h alternating temperatures, seeds were in light during the high-temperature period and in the dark during the low-temperature period. The light source was 40-W white fluorescent tubes, and the irradiance at the level of the seeds was about 20 µmol·m–2·s–1 on a double layer of filter paper moistened with distilled water. Four concurrent trials of 30 seeds were used for each set of conditions. Observations were made at 1 or 2 d, and germinated seeds were counted and removed. The filter paper was remoistened with distilled water regularly.

Germination at temperatures simulating outdoors conditions
Seeds were placed at 25°/15°C for 90 d, moved to 15°/5°C for 60 d, and moved to 5°C in a simulation of outdoor temperatures. Temperatures of 25°/15°, 15°/5°, and 5°C corresponded roughly to the maximum and minimum temperatures in the outdoors from mid-June to mid-September, from mid-September to the beginning of November, and from the beginning of November to the end of December, respectively. The date of seed collection, control of bacteria, the number of seeds, the method of sowing, light conditions, and observations were the same here and in the experiments below as in the experiment above on temperature.

Effects of high temperatures (25°/15°C) before germination at various low temperatures
In an experiment examining the effects of high-temperature treatment on germination at four low temperatures, we kept seeds at 25°/15°C for 90 d and then moved them to 0°, 5°, 10°, or 15°C. At 0°C, seeds were kept in the dark continuously because of the incubator's limited capacity. Germination at various low temperatures was observed as in the above experiment.

Effects of various temperatures before germination at 5°C
In an experiment done to identify the optimum temperature before germination, seeds were kept at 25°/15°, 20°, 25°, or 30°C for 90 d and then moved to 5°C. Germination was observed as in the above experiments.

Effects of length of high-temperature treatment before germination at 5°C
In this experiment, we examined which of four periods of high-temperature treatment was effective for the germination. Seeds were placed at 25°/15°C for 30 d, 60 d, 90 d, or 120 d and then moved to 5°C.

Effects of temperature on embryo growth
In an examination of the effects of temperature on embryo growth, seeds were kept at 0°, 5°, or 25°/15°C throughout the experiment, or else at 25°/15°C for 90 d before being moved to 5°C. The lengths of ten embryos were measured on 25 June, 25 July, 25 August, 23 September, 22 October, 21 November, and 21 December as in the experiment on the phenology of embryo growth in the outdoors.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
Phenology of embryo growth in the outdoor pot experiments
The mean maximum and minimum temperatures were 32°/17°C from 25 June to 15 September and 14°/6°C from 16 September to 30 November 1999 (Fig. 1). The mean embryo length of fresh seeds on 25 June was 0.33 ± 0.04 mm, which was 8.1% of mean seed length (4.09 ± 0.35 mm). Embryos grew little until they started slow growth in August. From the beginning of September, when temperatures were medium or low, embryos grew rapidly and reached a mean of 3.23 mm on 21 November, by which time 93% of seeds had germinated. The large SD for embryo length on 21 November was partly accounted for by the small number of embryos left to be measured.



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  		Fig. 1. Temperatures in the field and mean lengths (±1 SD) of embryos of Erythronium japonicum. Lengths of ten embryos were measured on 25 June, and on the same day, 150 seeds were buried in leaf mold. On 26 July, 25 August, 23 September, and 22 October, the seeds were unburied, ten were chosen at random, and lengths of embryos were measured. On 21 November, only three embryos could be measured; all other seeds had germinated

 
Phenology of germination in the outdoor pot experiments
Seeds sown on 25 June 1999 did not germinate immediately. After the high temperatures of summer and medium temperatures of autumn, germination was first detected on 5 November (Fig. 2). Many remaining seeds germinated rapidly within November, with minimum and maximum temperatures of 8°/0°C, and 86% of seeds had germinated by 3 December.



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  		Fig. 2. Temperatures in the field and mean percentage of seeds that germinated (±1 SD). Three lots of 100 seeds were buried in leaf mold, and germinated seeds were counted monthly and removed

 
Phenology of seedling emergence in the outdoor pot experiments
The mean maximum and minimum temperatures were 24° and 16°C from 16 June 1998 to 15 September, 14°/6°C (maximum/minimum) from 16 September to 30 November, 0°/0°C from 1 December to 5 April, and 10°/1°C from 6 to 22 April (Fig. 3). Seedlings emerged a considerable time after germinating, although the soil cover was thin. Cotyledons of seeds sown on 16 June 1998 began to emerge on 1 December 1999 under the snow; the temperature was 0°C at the time of the observation. More seedlings emerged under the snow, and we observed cotyledons surviving even when enclosed in ice. On 16 March 1999, 28% of the seedlings were about 1–4 cm long. Seedling emergence was 82% on 15 April, 1 wk after snowmelt ended. By 22 April, 86% of seeds had emerged.



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  		Fig. 3. Temperatures in the field and mean percentage of seedlings that emerged (±1 SD). Three lots of 100 seeds were sown on soil (a 1 : 1 mixture of peat moss and vermiculite) and covered with 2–3 mm of sieved soil. Seedlings that appeared above the soil surface were counted and removed monthly

 
Effects of constant or alternating temperatures on germination
Of the various conditions tried, a continuous temperature of 10°C and alternating temperatures of 15°/5°C (light 12 h/dark 12 h) led to seed germination, which was seen first 130 d after sowing (Fig. 4). At 200 d, germination at 10° and 15°/5°C reached 84% and 74%, respectively.



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  		Fig. 4. Effects of constant or alternating temperatures on germination. Seeds were incubated at five constant temperatures (0°, 5°, 10°, 15°, and 20°C) and two regimens of alternating temperatures with 12 h at each temperature (15°/5°C and 20°/10°C). At constant temperatures, seeds were exposed to light for 12 h each day; and at 12/12 h alternating temperatures, seeds were in light during the high-temperature period and in the dark during the low-temperature period. Conditions that did not lead to germination are not included in the figure. Four lots of 30 seeds were treated at each temperature or pair of temperatures. Observations were made daily or every other day, but datum points are for results obtained every fifth day

 
Germination at temperatures simulating outdoors conditions
Seeds did not germinate during the 90-d incubation at alternating temperatures of 25°/15°C (light 12 h/dark 12 h) (Fig. 5). However, 45 d after being moved to 15°/5°C, seeds began to germinate, and germination was 100% after 30 d at 5°C. The results of this experiment and the preceding one suggested that high (25°/15°C) and medium (15°/5°C) temperatures promoted the germination of E. japonicum seeds moved to a low temperature later.



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  		Fig. 5. Germination at temperatures simulating field conditions. Seeds were incubated with 12 h of light and 12 h of dark at 25°/15°C for 90 d and then moved to 15°/5°C for 60 d before being placed at 5°C in a simulation of field temperatures from mid-June to the end of December. Four lots of 30 seeds were used. Observations were as in Fig. 4

 
Effects of high temperatures (25°/15°C) before germination at various low temperatures
Seeds did not germinate within 90 d at the high temperatures of 25°/15°C, as before, but 40 d after being moved to 0°, 5°, or 10°C, they began to germinate, with 88%, 92%, and 99% germination, respectively, by 200 d after sowing (Fig. 6). These final germination percentages were not significantly different at the three temperatures (Sheffé's test, P < 0.05 level). Seeds did not germinate when kept at 25°/15°C for 90 d and then at 15°C for 110 d.



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  		Fig. 6. Effects of high temperatures (25°/15°C) before germination at various low temperatures. After the high temperatures for 90 d, seeds were moved to 0°, 5°, 10°, or 15°C. Four lots of 30 seeds were used for each set of conditions. Observations were as in the legend of Fig. 4

 
Effects of various high temperatures before germination at 5°C
The high temperature of 25°/15° or 20°C for 90 d allowed later germination at 5°C, and germination exceeded 90% (Fig. 7). The high temperature of 25° or 30°C also allowed later germination at 5°C, but germination was <30%.



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  		Fig. 7.  Effects of various high temperatures before germination at 5°C. Seeds were placed at 25°/15°, 20°, 25°, or 30°C for 90 d and moved to 5°C. Four lots of 30 seeds were used for each set of conditions. Observations were as in Fig. 4

 
Effects of length of high-temperature treatment before germination at 5°C
High temperatures of 25°/15°C for 30 d, 60 d, 90 d, or 120 d followed by incubation at 5°C gave final germination percentages of 84%, 93%, 92%, and 94%, respectively (Fig. 8). In other words, 30 d at the high temperature was long enough to allow germination later at a low temperature. The days to germination after sowing were greater with longer periods of high temperature. However, the days to germination after seeds were moved to 5°C were fewer with longer periods of high temperature. When seeds were incubated at 5°C after the high temperatures for 30 d, 60 d, 90 d, or 120 d, the germination started at 90 d, 60 d, 48 d, or 41 d, respectively, after the move to 5°C.



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  		Fig. 8. Effects of length of high-temperature treatment before germination at 5°C. Seeds were placed at 25°/15°C for 30 d, 60 d, 90 d, or 120 d and moved to 5°C. Four lots of 30 seeds were used for each set of conditions. Observations were as in the legend of Fig. 4

 
Effects of temperature on embryo growth
Embryos of seeds kept at 0°, 5°, 25°/15°, or 25°/15°C for 90 d followed by 5°C were seen to grow little until they were measured on 25 August, 63 d after incubation (Fig. 9). Embryos kept at 0° or 5°C did not grow at any time. Embryos placed at 25°/15°C grew, but their final mean length was 1.6 mm, about half that after 25°/15°C for 90 d followed by 5°C, and the seeds had not germinated by the end of the experiment. However, embryos kept at 25°/15°C for 90 d followed by 5°C grew rapidly after day 63, and 95% of the seeds had germinated by day 180 (21 December). The course of embryo growth at 25°/15°C for 90 d followed by 5°C was similar to that in the outdoors.



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  		Fig. 9. Effects of temperature on embryo growth. Seeds were kept at 0°, 5°, or 25°/15°C throughout the experiment or else at 25°/15 °C for 90 d before being moved to 5°C. The mean lengths (±1 SD) of ten embryos measured on 25 June, 26 July, 25 August, 23 September, 22 October, 21 November, and 21 December are shown

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
Germination and seedling phenology
Embryos in freshly matured seeds of E. japonicum were a mean of 0.33 mm long, much less than the mean length of the seeds, 4.09 mm. Embryos of freshly matured seeds of E. albidum (Baskin and Baskin, 1985a ), E. grandiflorum (Baskin, Meyer, and Baskin, 1995 ), E. americanum, and E. rostratum (Baskin and Baskin, 1998 ) also are small.

Seeds of E. japonicum are dispersed in mid-June in Hokkaido, but embryos did not elongate in the high temperatures of summer. Embryos grew rapidly from September to November as the temperature decreased at 14°/6°C. After the embryos had elongated enough, germination started at once (in early November); in 1999, 86% had germinated between 5 November and 3 December at 8°/0°C.

Embryos of E. albidum also were initially underdeveloped; embryos began to elongate in September, and the elongation was greatest in October and November when they were placed in a garden. However, such embryos continue to elongate during the winter, and germination (defined as we did here) was first detected on 15 February 1984 (Baskin and Baskin, 1985a ). Also in the nonheated greenhouse experiments, seeds germinated in the period from 21 to 28 February 1983 at 14°/4°C; 90% had germinated by the period from 7 to 14 March 1983 at 14°/4°C; and 24% had also germinated in the period from 14 to 20 February 1984 when at 19°/7°C (Baskin and Baskin, 1985a ).

To summarize our results and theirs, embryo elongation and germination of E. japonicum is brought to completion at low temperatures within the year after the high temperature of the summer, although embryo elongation of E. albidum continues during the winter and germination starts in late winter at medium temperatures.

The outdoor temperatures until November in their experiments and ours were similar, but the temperatures during the winter differed greatly. In winter, E. japonicum was grown in Sapporo, Hokkaido at a fairly constant 0°C because of the snow cover. Erythronium albidum was grown in Lexington, Kentucky, USA, where the temperature from December to February is very low, sometimes as low as –20°C (Baskin and Baskin, 1985a ). The results from their outdoor experiments might mean that the severe winter delayed the germination of E. albidum. However, as described in the following section, our laboratory experiments showed that the different germination phenology of the two species arose from their different temperature responses not from the different temperatures in the outdoor experiments.

We found that germination of E. japonicum in the strict sense had already ended within November, that about 30% of the cotyledons emerged under the snow, and that most cotyledons had emerged by early April around snowmelt. Many plants whose cotyledons do not emerge immediately after radicle emergence are known. This phenomenon is referred to as "epicotyl dormancy" (Baskin and Baskin, 1998 ). Erythronium japonicum also seems to have epicotyl dormancy.

Effects of temperature on embryo elongation and germination
Embryos of E. japonicum did not grow well when kept at only the high temperatures of 25°/15°C or only the low temperatures of 0° or 5°C. Embryos grew rapidly and seeds germinated when kept at 25°/15°C for 90 d and then at 5°C. However, embryos could elongate at temperatures near 10°C, because seeds placed at 10° or 15°/5°C germinated but seeds placed at 0°, 5°, 15°, 20° or 20°/10°C did not germinate.

In many species, the temperature range for germination widens after dormancy is broken (Baskin and Baskin, 1985b ; Kondo, Maenaka, and Takahashi, 1992 ; Kondo, 1993 ). With E. japonicum, if seeds were kept at high temperatures first, the germination temperature widened to the low temperatures of 0°, 5°, and 10°C. Therefore, an initial period of high temperatures may be one factor that breaks dormancy; this would be consistent with the finding in the outdoor experiment that seeds germinated in November at 8°/0°C after the summer. A review of papers reporting germination of seeds of plants in the genus Erythronium (Griswold, 1936 ; Pelton, 1956 ; Muller, 1978 ; Kawano, Hiratsuka, and Hayashi, 1982 ; Baskin and Baskin, 1985a ; Baskin, Meyer, and Baskin, 1995 ) did not reveal any report that initial high temperatures widens the temperature range for germination. Of the temperatures we tried, the most effective high temperatures for germination were 20° or 25°/15°C. After such high temperatures, the temperature for germination was widened to 0°–10°C.

However, seeds of E. albidum germinated to high percentages at 15°/6°C following 12 wk at 30°/15°C along with 12 wk at 5°C (Baskin and Baskin, 1985a ).

We can explain the germination phenology of E. japonicum in the outdoors by temperature requirements of seeds from our results. In the outdoors, seeds are dispersed in mid-June in Hokkaido, Japan, without germinating immediately. Their embryos are underdeveloped when seeds are dispersed. High temperatures followed by medium or low temperatures are needed to elongate their embryos. Germination occurs at low temperatures after the full elongation of embryo. Therefore, seeds do not germinate immediately after their dispersal, and seeds germinate in late autumn after summer heat. After germination, seedling emergence is delayed under the snow, and most seedlings are observed in early April around the snowmelt.


   FOOTNOTES
 
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4 Author for reprint requests (FAX: +81-11-667-8837; kondo{at}res.agr.hokudai.ac.jp ) Back


   LITERATURE CITED
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Baskin C. C. J. M. Baskin 1998 Seeds: ecology, biogeography, and evolution of dormancy and germination. Academic Press, New York, New York, USA

Baskin J. M. C. C. Baskin 1985a Seed germination ecophysiology of the woodland spring geophyte Erythronium albidum. Botanical Gazette 146: 130-136[CrossRef]

Baskin J. M. C. C. Baskin 1985b The annual dormancy cycle in buried weed seeds: a continuum. Bioscience 35: 492-498[CrossRef][ISI]

Baskin C. C. S. E. Meyer J. M. Baskin 1995 Two types of morphophysiological dormancy in seeds of two genera (Osmorhiza and Erythronium) with an Arcto-Tertiary distribution pattern. American Journal of Botany 82: 293-298[CrossRef][ISI]

Griswold S. M. 1936 Effect of alternate moistening and drying on germination of seeds of western range plants. Botanical Gazette 98: 243-269

Kawano S. A. Hiratsuka K. Hayashi 1982 Life history characteristics and survivorship of Erythronium japonicum: the productive and reproductive biology of flowering plants, V. Oikos 38: 129-149[CrossRef][ISI]

Kawano S. Y. Nagai 1982 Further observations on the reproductive biology of Erythronium japonicum (L.) DECNE. (Liliaceae). Journal of Phytogeography and Taxonomy 30: 90-97

Kondo T. 1993 Germination characteristics of wildflower. Journal of the Japanese Institute of Landscape Architects 57: 121-128 (in Japanese with English summary)

Kondo T. H. Maenaka R. Takahashi 1992 Propagation and vegetational management of wild flowers: germination, cutting propagation, and frequency and timing of mowing for extending the flowering season of Aster ageratoides subsp. ovatus Kitam. Journal of the Japanese Society of Revegetation Technology 17: 193-202 (in Japanese with English summary)

Muller R. N. 1978 The phenology, growth and ecosystem dynamics of Erythronium americanum in the northern hardwood forest. Ecological Monographs 48: 1-20

Ohkawara K. S. Higashi M. Ohara 1996 Effects of ants, ground beetles and the seed-fall patterns on myrmecochory of Erythronium japonicum Decne. (Liliaceae). Oecologia 106: 500-506[CrossRef][ISI]

Ohwi J. 1983 New flora of Japan. Shibundo, Tokyo (in Japanese)

Pelton J. 1956 A study of seed dormancy in eighteen species of high altitude Colorado plants. Butler University Botanical Studies 13: 74-84

Sawada S. S. Chiba Y. Sawaguchi N. Nagasawa 1997 Dry matter production, population structure and environmental conditions of the spring ephemeral Erythronium japonicum growing in various habitats differing in sunlight exposure in cool temperate Japan. Ecological Research 12: 89-99[CrossRef][ISI]

Takada T. S. Nakayama S. Kawano 1998 A sensitivity analysis of the population dynamics of Erythronium japonicum, a liliaceous perennial. Plant Species Biology 13: 117-127

Yokoi Y. 1976 Growth and reproduction in higher plants. II. Analytical study of growth and reproduction of Erythronium japonicum. Botanical Magazine Tokyo 89: 15-31[CrossRef][ISI]




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