The Morphological Variation of the Genus Rhododendron (Ericaceae) in Himalayan Ranges of Bhutan

  • Sangay Namgay Department of Biology, Faculty of Science, Prince of Songkla University, Hat Yai, 90112, Songkhla, THAILAND
  • Kitichate Sridith Department of Biology, Faculty of Science, Prince of Songkla University, Hat Yai, 90112, Songkhla, THAILAND
Keywords: morphology, pollination syndrome, Rhododendron

Abstract

Bhutan Himalayan ranges harbor 46 species of Rhododendron and contributes four percent of the genus in the world. The genus Rhododendron is associated with morphologically diverse, complex vegetative and floral traits. The variation of floral traits of rhododendrons might have attributed due to the pollinators and adaptive preference resulting in the evolution of floral complexity. However, there is a paucity of scientific studies concerning the vegetative and reproductive morphology of rhododendrons and pollinators. A comparative morphological study was investigated on 30 species of Rhododendron from different geographical locations of Bhutan. We studied the interspecific variation of seed and pollen morphology among the selected species. Casual pollinator observations were also examined to identify the potential pollinators and visitors through in-person and binocular. Eight different floral types and two seed types were identified from the present study. We suggest that the floral morphology and distribution of Rhododendron floral types over the landscape may reflect their adaptive value of the plant-pollinator interactions. Additionally, seed traits might have influenced the dispersal ability and colonization of species. Further in-depth explorations on floral development, pollination ecology, and seed developmental allometry may offer a broader understanding of the floral evolution, specialization in plant-pollinator interaction in angiosperm, and their adaptation to the unique environmental cline of the Himalayas.

References

Basnett, S., Ganesan, R. and Devy, S.M. 2019. Floral traits determine pollinator visitation in Rhododendron species across an elevation gradient in the Sikkim Himalaya. Alpine Botany 129: 81–94.

Berry, E., Sharma, S.K., Pandit, M.K. and Geeta, R. 2017. Evolutionary correlation between floral monosymmetry and corolla pigmentation patterns in Rhododendron. Plant Systematics and Evolution, 304: 219–230.

Bharali, S., Paul, A., Khan, M.L. and Singha, L.B. 2011. Species diversity and community structure of a temperate mixed Rhododendron forest along an altitudinal gradient in West Siang district of Arunachal Pradesh, India. Nature and Science, 9: 125–140.

Campbell, D.R., Waser, N.M. and Price, M.V. 1996. Mechanisms of hummingbird-mediated selection for flower width in Ipomopsis aggregata. Ecology, 77: 1463–1472.

Chamberlain, D., Hyam, R., Argent, G., Fairweather, G. and Walter, K.S. 1996. The genus Rhododendron: its classification and synonymy. Royal Botanic Garden Edinburg, Edinburg. 181 pp.

Cullen, J. 2005. Hardy Rhododendron Species. A Guide to identification. Royal Botanic Garden Edinburg, Timber Press. 496 pp.

Dafni, A. and Kevan, P.G. 1997. Flower Size and Shape: Implications in Pollination. Israel Journal of Plant Science, 45: 201–211.

Davidian, H.H. 1989. The Rhododendron Species Volume II Elepidotes Species, Series Arboreum Lacteum, Timber Press, Inc. Batsford, London. 431 pp.

Faegri, K. and van der Pijl., L. 1979. Principles of Pollination Ecology, Pergamon Press, New York. 244 pp.

Fenster, C.B. 1991. Selection on floral morphology by hummingbirds. Biotropica, 23: 98–101.

Fenster, C.B., Armbruster, W.S., Wilson, P., Dudash, M.R. and Thomson, J.D. 2004. Pollination syndromes and floral specialization. Annual Review of Ecology Evolution and Systematics, 35: 375–403.

Georgian, E., Fang, Z.D., Emshwiller, E. and Pidgeon, A. 2015. The pollination ecology of Rhododendron floccigerum Franchet (Ericaceae) in Weixi, Yunnan Province, China. Journal of Pollination Ecology, 16: 72–81.

Galen, C. and Cuba, J. 2001. Down the tube: pollinators and the evolution of flower shape in the alpine skypilot, Polemonium viscosum. Evolution, 55: 1963–1971.

Long, D.G. 1991. 1. Rhododendron. In: Grierson, A.J.C. and Long, D.G. (Eds.) Flora of Bhutan volume 2, part 1, Royal Botanical Garden, Edinburgh, pp. 358–387.

Grytnes, J.A. and Vetaas, O.R. 2002. Species richness and elevation: a comparison between null models and interpolated plant species richness along the Himalayan altitudinal gradient, Nepal. The American Naturalist, 159: 294–304.

Guo, H., Mazer, S.J. and Pu, G. 2010. Geographic variation in seed mass within and among nine species of Pedicularis (Orobanchaceae): effects of elevation, plant size and seed number per fruit. Journal of Ecology, 98: 1232–1242.

Hesse, M., Vogel, S. and Halbritter, H. 2000. Thread-forming structures in angiosperm anthers: their diverse role in pollination ecology. Plant Systematics and Evolution, 222: 281–292.

Huang, Z.H., Song, Y.P. and Huang, S.Q. 2017. Evidence for passerine bird pollination in Rhododendron species. The Annals of Botany Plants, 9: 1–10.

Jamtsho, K. and Sridith, K. 2015. Exploring the patterns of alpine vegetation of Eastern Bhutan: a case study from the Merak Himalaya. SpringerPlus, 4: 304.

Johnson, S.D. 2010. The pollination niche and its role in the diversification and maintenance of the southern African flora. Philosophical Transaction of the Royal Society B: Biological Sciences, 365: 499–516.

Körner, C. 1998. A re-assessment of high elevation treeline positions and their explanation. Oecologia 115: 445–459.

Kudo, G. 1993. Relationship between flowering time and fruit set of entomophilous alpine shrub, Rhododendron aureum (Ericaceae) inhabiting snow patches. American Journal of Botany, 80: 1300–1304.

Namgay, S. and Sridith, K. 2020. Distribution pattern of genus Rhododendron in Bhutan Himalayan range. ScienceAsia, 46: 429.

Pellissier, L., Pottier, J., Vittoz, P., Dubuis, A. and Guisan, A. 2010. Spatial pattern of floral morphology: possible insight into the effects of pollinators on plant distributions. Oikos, 119: 1805–1813.

Pradhan, R. 1999. Wild Rhododendrons of Bhutan. Quality printers Pvt. Ltd, Kathmandu, Nepal. 53 pp.

Sarwar, A.K.M.G. and Takahashi, H. 2013. Pollen morphology of Rhododendron L. and related genera and its taxonomic significance. Bangladesh Journal of Plant Taxonomy, 20: 185–199.

Scaven, V.L. and Rafferty, N.E. 2013. Physiological effects of climate warming on flowering plants and insect pollinators and potential consequences for their interaction. Current Zoology, 59: 148–426.

Singh, K.K., Rai, L.K. and Gurung, B. 2009. Conservation of rhododendrons in Sikkim Himalaya: an overview. World Journal of Agricultural Science, 5: 284–296.

Skvarla, J.J., Raven, P.H., Chisoe, W.F. and Sharp, M. 1978. An ultrastructural study of viscin threads in Onagraceae pollen. Pollen Spores, 20: 5–143.

Song, Y.P., Huang, Z.H. and Huang, S.Q. 2019. Pollen aggregation by viscin threads in Rhododendron varies with pollinator. New Phytologist, 221: 1150–1159.

Spierenburg, P. 2005. Birds in Bhutan, status and distribution. Oriental Bird Club, Bedford, UK. 383 pp.

Smith, S.D., Ané, C. and Baura, D.A. 2008. The role of pollinator shifts in the floral diversification of Iochroma (Solanaceae). Evolution, 62: 793–806.

Stevens, P.F. 1975. The altitudinal and geographical distributions of flower types in Rhododendron section Vireya, especially in the Papuasian species, and their significance. Botanical Journal of the Linnean Society, 72: 1–33.

Wang, X., Arora, R., Horner, H. and Krebs, S. 2008. Structural adaptation in overwintering leaves of thermonastic and nonthermonastic Rhododendron species. Journal of the American Society for Horticultural Science, 133: 768–776.

Wang, Y., Wang, J., Lai, L., Jiang, L., Zhuang, P., Zhang, L., Zheng, Y., Baskin, J.M. and Baskin, C.C. 2014. Geographic variation in seed traits within and among forty-two species of Rhododendron (Ericaceae) on the Tibetan plateau: relationships with altitude, habitat, plant height, and phylogeny. Ecology and Evolution, 4: 1913–1923.

Willmer, P. 2011. Pollination and floral ecology. Princeton university Press, New Jersey. 778 pp.

Yoichi, W., Minamitani, T., Oh, S.H., Nagano, A.j., Abe, H. and Yukawa, T. 2019. New taxa of Rhododedron tschonoskii alliance (Ericaceae) from East Asia. PhytoKeys, 134: 97–114.

Zetter, R. and Hesse, M. 1996. The morphology of pollen tetrads and viscin threads in some tertiary, Rhododendron-Like Ericaceae. Grana, 35: 285–294.
Published
2021-07-29
How to Cite
Namgay, S., & Sridith, K. (2021). The Morphological Variation of the Genus Rhododendron (Ericaceae) in Himalayan Ranges of Bhutan. Tropical Natural History, 21(2), 299-320. Retrieved from https://li01.tci-thaijo.org/index.php/tnh/article/view/251702
Section
Original Articles