The Chinese orchid, _Cymbidium serratum_, is pollinated by the wild mountain mouse _Rattus fulvescens_. The flowers use both odor and colour as attractants, and provide labellum as food reward for the pollinators. The mice pollinate the flowers during their endeavour to eat the labellums

Li Dong

Xiao-Kai Ma

Yang Zhang

Yong Wang

English

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The unique mouse-pollination in an orchid species 
 (Yong Wang1, Yang Zhang1,2, Xiao-Kai Ma1, Li Dong1,3) 
1Biological  Sciences Department, Shaanxi University of Technology, Chaoyang Road, 
Hanzhong, Shaanxi 723001, China 
2 Wuhan Botanical Garden, The Chinese Academy of Sciences, Wuhan 430074, China 
3 College of Horticulture and Landscape Architecture, Southwest University, 
Chongqing 400715, China 
The Chinese orchid, Cymbidium serratum, is pollinated by wild mountain mouse, 
Rattus fulvescens. The flowers use both ordor and colour as attractants, and 
provide labellum as food reward for the pollinators. The mice pollinate the flowers 
during their endeavour to eat the labellums. 
Charles Darwin was not exaggerating when he renounced that the various 
contrivances and adaptation of orchids vastly transcend those which the most fertile 
imagination of the world's most imaginative man could dream up with unlimited time at 
his disposal. Although the very large Orchid Family, with approximately 35,000 species, 
is renowned for its enormous diversity of pollination mechanisms, their pollinators are 
fairly monotonous - mainly insects and rarely birds. Here we describe the unique mouse 
pollination in an Ochidaceae species, Cymbidium serratum. This is the first record of 
mammal pollinator in Orchidaceae.  
Cymbidium serratum is a terrestrial orchid found in the mountainous area of 
central and South China. Our studying location is Han Zhong area, Shaanxi province of 
Central China. The plant grows on humus-rich woody slopes in scattered clumps 
(Density ) and its altitudinal rang confined to 500-1000m in studying area. The 
flowering period is from the end of February to the end of March, lasting for about a 
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month. 1-12 terminal flowers open in the same time on one individual. Scapes are 18.3 
± 6.2 cm (n = 20) in length. Sepals and lateral petals are green, but labellum is white 
and dark-red spotted. Because the flowers are facing slightly downward, the labellum 
are invisible to observers from above (Fig. 1a), but conspicuous from lower (Fig. 1b). 
Although they are described as unscented by earlier researchers1,2, we found that they 
produce an odor smelled like fermented fodder to human nose. The smelling is weak in 
the day but stronger in the night. The tip of the column curves and covers stigma in 72 
hours after successfully pollinated. Artificial experiment showed that both self-
pollinating and cross-pollinating fruited well, but cannot set fruit when bagged, 
indicating that spontaneous self-pollinating is absent in the species. 
We studied 6 natural populations of C. serratum for 5 continuous years and found 
that wild mountain mouse (Rattus fulvescens) is the only pollinator of the plant. The 
mouse is middle size (body length about 13 cm, tail length about 17 cm) and widely 
distributed in mountainous area in central and south China. They like woodlands, 
cultivated areas, and forests. The sense of smell is highly developed, and these rodents 
can detect the exact location of buried seeds without having to dig at random in a 
general area. The diet of the Wood Mouse consists of roots, grains, seeds, berries, nuts, 
grasses, fruits and insects3. They are nocturnal or crepuscular. They are active from 
nightfall to dayspring. The mouse approaches a flowering clump attracted by the smell, 
ultimately gets closely enough to be guided visually to eat the labellum of the flower 
standing on hind legs. During their visiting, the upper side of the nose stick to vicidium, 
then drag out the pollinium. The anther cap may function to prevent geitonogamy in one 
plant4. After finished with one flower, it usually turns to another one until all labellum 
on the plant are eaten up (Fig 1c; Fig1d; Fig 1e). The anther cap falls off either 
immediately of during their moving around on the ground. The pollinium may have the 
chance to adhere to the stigma of next flower when the mouse visits another plant. A 
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wild mountain mouse could move around in an area of 50-80m in diameter and possibly 
visit 10-20 clumps of C. serratum one night. 
Unlike insect pollinated ones, the flowers of C. serratum are neither bright 
coloured nor aromatic. They adapt to mouse pollination in several ways. The flowers 
are basically dull green in colour. The bright coloured succulent labellum is favoured by 
wild mountain mouse. According to our experience, the labellum tastes slightly sweet, 
but the other flower parts including the lateral petals and the sepals tastes slightly bitter 
to human. We consider this could explain why the mouse is merely interested in 
labellum and leave the other parts intact. The plant flowers in early spring when the 
mice are active and other food resources are scare. Since the body lengths of the mice 
are similar to the height of the flowers (about 12.7 ± 6 cm (n = 20) above ground), the 
mice can easily get the flowers. The odor production is synchronized with the activity of 
the mouse. The distance between column and lip petal is about 9 ± 1.5mm (n = 20), 
similar to the height of the upper jaw of the mouse (about 12 mm). When forging on the 
flower, the upper side of their snout can easily contact with the pollinium.  
The pollination mechanism in C. serratum is very unique and different from that 
in other known rodent pollinated plants, which provide nectar as reward to those rodent 
pollinators. Rodent pollinating plants tend to have robust flowers with dull coloration, 
abundant pollen, copious amounts of nectar, exerted styles and stamens, and special 
structures called mammal guards5, 6, 7. Since C. serritum provids pollinators with 
labellum instead of nectar as food reward, its flower is relatively slender and nectarless. 
Unlike the exerted styles and stamens in other rodent pollinated flowers, the stigmas 
and polliniums in C. serratum positioned in a way that they can contacted with the body 
of the animals only when the pollinators feeds on the labellum in certain posture. 
Although the plant doesn’t have mammal guard, it successfully prevent the destruction 
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by mouse, probably by it special distribution of certain chemical contents in deferent 
organs. 
 Of many varied interaction between plants and animals, one of the most 
unexpected is pollination of flowers by rodents. The phenomenon was first recorded in 
Protea shrubs (Proteacea) in the 1970s8, and until now, was thought to be confined to 
shrubs belongs to three dicotyledon families: Proteacea, Loasaceae, and 
Melastomataceae, and one monocotyledon family, Hyacinthaceae5. Our finding adds to 
the diversity of both pollinating mechanisms in Orchidaceae and rodent pollinating 
plant groups. Closely related species may own different pollination mechanisms. The 
closest relative, or the sibling species, of C. serratum, C. georingii1, is strongly fragrant 
and a typical bee pollinating species that owns food-deceptive pollination mechanism9. 
The unique pollination mechanism of C. serratum may evolve independently in the 
family. 
1. Chen S.-C. Floral of China (Science Press, Beijing, 1999).  
2. Liu, Z.-J., Chen, S.-C. & Ru, Z-Z. The Genus Cymbidium in China (Science Press, 
Beijing, 2006) 
3. Nowak, R. M. Walker's Mammals of the World 5th edn Vol II (Johns Hopkins 
University Press, Baltimore 1991). 
4. Cheng J., Liu S.-Y., He R., Wei X.-L. & Luo Y.-B. Biodiv. Sci. 15, 608-617 (2007) 
5. Steven, D. J., Anton, P. & Jeremy, M. Am. J. Bot. 88, 1768-1773(2001).  
6. Carthew, S. M. & Goldingay, R. L. Tre. Eco. Evol. 12, 104-108(1997). 
7. Andrea, A. C. & Alicia, N. S. Pl. Sys. Evol. 221, 113-128(1998). 
8. Wiens, D. & Rourk. J. P. Nature 276, 71-73(1978). 
9. Yu, X.-H., Luo, Y.-B. & Dong, M. J. Sys. Evo. 46, 163-174 (2008).  
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Acknowledgements  The research work was funded by Doctoral Research Fund of Shaanxi University of 
Technology (SLGQD0512).  
Correspondence and requests for materials should be addressed to Yong Wang (waldenwy@gmail.com). 
Figure 1  Mouse pollination in Cymbidium serratum. a, A flowering clump 
observed from above, with flowers dull green and insignificant. b, A flowering 
clumps observed at ground level, with labellum bright colored and conspicuous. 
c, A flower visited by wild mountain mouse, note that the pollinarium has been 
removed, the labellum has been eaten, and the other floral parts are intact. 
Lower arrow, the position where labellum once attached. Upper arrow, the 
position where pollinium once located.  d, A wild mountain mouse visiting a 
flower. e, A wild mountain mouse with pollinarium stuck on its snout after 
visiting the flowers of C. serratum. Arrow, pollinium. 
 
 
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The unique mouse pollination in an orchid species

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The unique mouse pollination in an orchid species

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