International Journal of Biology; Vol. 4, No. 3; 2012ISSN 1916-9671
E-ISSN 1916-968X
Published by Canadian Center of Science and Education

Characteristics of the Falling Speed of Japanese Orchid Seeds
Syunsuke Kiyohara1, Hirokazu Fukunaga2 & Shinichiro Sawa1
1

Department of Sciences, Kumamoto University, Kumamoto, Japan

2

Tokushima-cho 3-35, Tokushima, Japan

Correspondence: Shinichiro Sawa, Department of Sciences, Graduate school of Science and Technology,
Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan. Tel: 81-963-423-439. E-mail:sawa@sci.kumamoto-u.ac.jp
Received: March 2, 2012doi:10.5539/ijb.v4n3p10

Accepted: March 20, 2012

Online Published: May 31, 2012

URL: http://dx.doi.org/10.5539/ijb.v4n3p10

Abstract
Orchid seeds, which are produced in abundance, are particularly small and light. Some orchid species are
anemochorous, i.e., bear seeds that are dispersed by wind. To characterize the seeds of Japanese orchids, wemeasured the size of seeds and embryos of 68 Japanese orchid species. Most orchid seeds had a length of 0.3 to 2
mm and a width of 0.07 to 0.2 mm. Embryo length and width were 0.1 to 0.3 mm and 0.04 to 0.2 mm,respectively. Twenty-seven orchid species produced 1000 to 350000 seeds per pod. Speeds of fall of 34 Japaneseorchid species were examined in order to obtain insight into their seed dispersal ability. Falling speeds ranged
from 4 to 30 cm/s. These results strongly suggest that seeds of Japanese orchids are also dispersed by wind andthus that most Japanese orchids are anemochorous species.
Keywords: Japanese orchids, wind, speed of fall of seeds, anemochorous, seed size, seed number
1. Introduction
The dispersal of seeds to a suitable habitat is a crucial event in the plant life cycle. Three major mechanisms
spread seeds; i.e., hitchhiking on animals, floating in water, and moving in the wind (Fenner, 1985). Most
anemochorous species produce particularly small and light seeds (Burrows, 1975). In some cases, seeds havewings that enable them to travel long distances (Burrows, 1973). Mathematical models have been developed to
predict the dispersal distances of various anemochorous seeds (Cremer, 1977; Murren & Ellison, 1996; 1998).
The orchid family is a morphologically diverse monocot. Because of their beautiful flowers, Orchidaceae plants
are important not only for biologists but also in the marketplace (Sawa et al., 2006; Fukunaga et al., 2008; Ejimaet al., 2011). The orchid produces dust seeds, with shapes that are adapted to the habitat of the orchid (Shimizu etal., 2012), and some orchids are considered to be anemochorous plants. However, orchid seeds have not been
well characterized. Here, we characterized the seeds and embryos of Japanese orchids, and determined the speedof fall of the seeds. We discuss correlations between orchid habitat and properties of the seed, and comment on
the evolution of this relationship.
2. Materials and Methods
2.1 Orchid Seeds
Orchid seeds were collected from their natural habitat in Japan. All seeds were dried using silica gel in a closed
plastic box at least for two weeks at room temperature.
2.2 Seed Number
All of the dried seeds in one pod were weighed. Based on mass, the seeds were divided into ten groups, and thenumber of seeds was counted in one of these groups. The number of seeds per pod was calculated as being ten
fold the counted number.
2.3 Seed Size
Seed size was examined using a stereomicroscope (Leica S8). Two-hundred seeds were evaluated per species.
Mean value was shown in Table 1.

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Vol. 4, No. 3; 2012

Table 1. Size and drop-speed of seeds on the native orchids in JapanSpecies

Bletilla striata
Bulbophyllum
inconspicuum
C. reflexa
C. tricarinata
C. native hybrid(Satuma)
C. schlechteri
C. discolor
Cephalanthera
erectaCremastra
appendiculata
Cymbidiumgoeringii
C.
dayanum
var.autro-japonicum
Dendrobium
moniliforme
D. tosaenseEpipactis thunbergii
Eria reptans
G. pubilabiata
Gastrodia confusa
G. nipponica
Goodyera velutina
G. macrantha
G. shlechtendaliana
Habenaria radiata
Lecanorchis
hokurikuensis
L. japonica
L. kiusiana
Liparis formosana
L. nervosa
L. odorata
Microtis formoana
Neofinetia falcata
Nervilia nipponica
Phajus minor
Spiranthes sinensis
var. anoena
Zeuxine agyokuana

Seed

EmbryoSeed No.

Drop-Length(/um)

Width (/um)

Length(/um)

Width (/um)

per pod(×1000)

Speed(cm/sec.)

1803
199

225
80488
149

209
70

30.2
-

23.5
11.91142
1086
957

134
163
122

144
178
144

86
91
77

-

8.9
11.1
8.4

939
831
1181

168
120
179

148
128
208

78
69
119

69.1
-

8.5
8.1
17.9

2302

127

280

110

-

9.1

1610

152

292

90

346.9

7.2

861

207

140

79

-

16.4

337

90

189

86

145.3

15.6

429
1923
207
2662
2619
2384
1814
1738
930
601
4560

87
234
86
147
109
102
78
81
102
230
127

175
259
128
217
201
193
257
226
207
238
168

86
137
81
79
68
72
91
76
65
190
84

42.6
1.4
10.1
48.8
1.1
1.4
2.4
-

7.8
11.8
18.6
7.6
6.0
4.9
5.9
6.5
8.5
29.8
4.5

4629
3760
708
683
458
376
302
581
752
459

152
98
94
102
98
112
85
131
112
95

174
120
104
109
120
188
219
113
183

86
64
54
49
60
73
74
47
84

3.7
3.1
13.5
18.1
37.9
90.6
1.8

4.6
4.3
5.5
4.2
9.5
15.6
26.9
3.4
3.6
11.5

1890

72

206

61

-

4.6

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2.4 Speed of Fall of the Seeds
A triangular prism, 25 cm each side and 2 m in height, was prepared, one surface of which was constructed ofpaper and two of transparent vinyl. Top surface was made of paper. A hole, 5 mm in diameter, was made in thetop surface. Seeds were dropped from the hole 20 times for each species, and measured the falling time. Fallingspeeds were calculated from the data of falling time and falling distance (25 cm). Mean value was shown in
Table 1.
3. Results and Discussion
We measured the seed size of 68 Japanese orchid species (Table 1). Orchid seeds are known to be small. In thisanalysis, we found that the seeds of Eria reptas had a length and width of 0.2 and 0.086 mm, respectively. Thissize is almost twice that of Zea mays (corn) or chestnut pollen grains. On the other hand, the seeds of theLechanorchis group were quite long, with L. japonica producing seeds that were 4.6 mm in length and 0.15 mm
in width. However, the embryo size of L. japonica was almost the same as that of other species (Table 1).
Seed number was also examined. Cymbidium goeringii produced 346900 seeds per pod (Table 1). In contrast,
Amitostigma gracile, Ponerorchis kurokamiana, and Tulotis ussuriensis produced only 900 seeds per pod. We
could not establish any correlation between seed size and seed number per pod.
To characterize seed dispersal ability, we measured the speed of fall of seeds from 34 Japanese orchids. The
speed of fall of the seeds of Taraxacum japonicum, which is a well-known anemochorous plant, was 30.0 cm/s.
Most of the seeds had slow speeds of fall (Table 1). Especially in the case of Habenaria dentata, Neofinetia
falcate, and Bletilla striata, the speed was 29.8, 26.9, and 23.5 cm/s, respectively. Thus, most of the Japaneseorchids could also be considered to be anemochorous plants. However, there was variation in the speed of fall ofJapanese orchid seeds, which suggests variation in their method of dispersal. In particular, H. dentate and B.
striata thrive in damp areas and on riverbanks, and their seeds can also be dispersed by water. The wind on theforest floor is weak, and orchids that grow in this habitat have to adapt to the weak-wind environment to disperse
their seeds. Thus, the seeds of orchids living on the forest floor may have evolved to be long, as increased length
reduces the speed of fall and increases the chance that the seed will be swept up by winds (Table 1; Shimizu etal., 2012).
Here we characterize the falling speed of Japanese orchid seeds. Most of the Japanese seeds can be considered as
anemochorous plants. However, they seemed to evolve the seed shape to adapt their habitat environment, i.e.
long and thin to reduce the seed falling speed. More detailed analysis of the seed shape will reveal how orchid
adapt various environment in the world.
References
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Burrows, F. M. (1975). Calculation of the primary trajectories of dust seeds, spores and pollen in unsteady winds.
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