Journal of Threatened Taxa | www.threatenedtaxa.org | 26 January 2025 | 17(1): 26426–26430
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.9386.17.1.26426-26430
#9386 | Received 28 August 2024 | Final received 15 October 2024 | Finally accepted 03 January 2025
Phenology of Rhododendron wattii Cowan (Ericales: Ericaceae) - a threatened plant of Nagaland, India
Imtilila Jing 1 & S.K. Chaturvedi 2
1,2 Department of Botany, Nagaland University, Lumami, Nagaland 798627, India.
1 jingimtilila@nagalanduniversity.ac.in (corresponding author), 2 sunchat1@rediffmail.com
Abstract: The paper deals with the flowering phenology of Rhododendron wattii Cowan (Ericaceae family), a threatened and endemic plant from Nagaland, northeastern India. The study was conducted at Dzukou Valley, Kohima District of Nagaland, on a single tree of R. wattii growing at an elevation of 2,600 m with no other tree of the same species in the vicinity. Flowering occurs from the end of February to April, and fruiting is observed from April to December. The flowers present in trusses of 18–25 flowers are pink with darker flecks and purplish basal blotches. They are foraged and pollinated by the Fire-tailed Sunbird Aethopyga ignicauda and bumble bees (Bombus spp.). The only attractant for the foragers is the nectar secreted in the five nectaries at the base of the corolla tube. Catastrophes like frequent forest fires and anthropogenic activities are responsible for the disappearance of this species.
Keywords: Aethopyga ignicauda, Bombus spp., Dzukou Valley, endemic, nectaries, northeastern India, Vulnerable.
Editor: Afroz Alam, Banasthali Vidyapith, Rajasthan, India. Date of publication: 26 January 2025 (online & print)
Citation: Jing, I. & S.K. Chaturvedi (2025). Phenology of Rhododendron wattii Cowan (Ericales: Ericaceae) - a threatened plant of Nagaland, India. Journal of Threatened Taxa 17(1): 26426–26430. https://doi.org/10.11609/jott.9386.17.1.26426-26430
Copyright: © Jing & Chaturvedi 2025. Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use, reproduction, and distribution of this article in any medium by providing adequate credit to the author(s) and the source of publication.
Funding: Ministry of Environment, Forest and Climate Change (MoEFCC), Govt. of India, New Delhi.
Competing interests: The authors declare no competing interests.
Acknowledgements: The authors are grateful to the Ministry of Environment, Forest and Climate Change, Govt. of India, New Delhi for financing the work. The authors thank the local guides for their support during the investigation. Thanks are due to Dr. A.A. Mao, director, Botanical Survey of India, Kolkata, for his valuable suggestions and authentic identification of the species and to Dr. Anwarrudin Choudhury for identifying the birds. The authors thank the Head of the Department of Botany for providing the infrastructural facilities while completing the present work.
The genus Rhododendron, belonging to the Ericaceae family, is one of the largest, most fascinating genera, with immense horticultural importance for its beautiful flowers and foliage. The genus is popular in Europe, America, Canada, Australia, and New Zealand. It occurs at higher altitudes, having ecological and economic importance in addition to its graceful flowers (Paul et al. 2005). The flowers of Rhododendrons are also considered sacred and offered in temples and monasteries (Mao et al. 2001). They display a wide range of morphological characteristics in their sizes, which range from less than 10 cm high to trees taller than 20 m (Williams et al. 2011).
Rhododendrons play a vital role in ecosystem services as they grow in areas of high rainfall and high humidity on acidic soils, conditions under which few plants would survive. They stabilise slopes in hilly areas and provide the structure of plant communities which support a wealth of biodiversity (Gibbs et al. 2011). According to Mainra et al. (2010), rhododendrons have phenological sensitivity to climate change and play a vital role in the ecological stability of ecosystems and as indicators of forest health. Thus, rhododendrons play important roles in maintaining biodiversity, preserving water & soil, and stabilizing the ecosystem. In the current century, the genetic resources of wild rhododendrons have been damaged severely due to the constant increase in human, social, & economic activities and some species have become highly threatened (Ma et al. 2014). Rhododendrons growing in high altitudes face the impact of disturbances due to various natural and anthropogenic factors (Mao et al. 2010). Natural threats include landslides and forest fires, which affect the rich growth of rhododendrons. Anthropogenic threats include fuel wood collection, small-scale extraction of timber, and collection of plants by locals for their graceful and magnificent flowers.
There are over 1,000 species of Rhododendrons worldwide. In India, 132 taxa are recorded, out of which 129 taxa are recorded from northeastern India. Northeastern states support the luxuriant growth of Rhododendrons, including many endemic species (Mao et al. 2017). According to the IUCN Red List, R. wattii is ‘Vulnerable’ due to population fragmentation and area of occupancy less than 500 km2 (Gibbs et al. 2011).
Rhododendron wattii was first collected by Sir George Watt from Japfu Hill ranges during his survey (1882-–1885) of Manipur and Nagaland (Mao et al. 2018). It is endemic to the Indian states of Manipur and Nagaland. It is a small tree attaining a height of 6–7.6 m (20–25 feet). Flowering occurs from March to April, and fruiting from April to December. During a field survey in 2012–2013, a single tree of R. wattii was located in Dzukou Valley, Nagaland, reported by Mao & Gogoi (2007) and later the tree was felled by the locals for firewood. Another tree was located in the surrounding hills of Dzukou Valley which is the subject of the present study. No seedlings or saplings were observed in the vicinity during the study period. The quick disappearance of this species from its natural habitat due to anthropogenic activities and natural disasters accompanied by poor regeneration of seedling survivability and recruitment failure could be one of the reasons for population decline and dwindling of R. wattii, which made it critically endangered in its natural habitat (Mao et al. 2017). In the present communication, an attempt has been made to highlight flowering phenology to provide valuable information on its conservation.
Materials and Methods
The study was carried out during 2012–2013 on a single tree of Rhododendron wattii found growing in its natural habitat at Dzukou Valley, Kohima District, Nagaland situated at 25033.387 N, 94004.707 E at an altitude of 2,600 m (Image 1). Regular field trips were conducted during the entire flowering period (February–April) to study the flowering phenology, the timing of the onset and termination of flowering, and the development of the ovary, fruit, and seed. The different floral visitors were observed and recorded during the study period. The foraging behaviour of the floral visitors were observed at different hours of the day. Field photographs and videos were taken using the Canon digital still camera with 8MP resolution. The species R. wattii was identified and authenticated by consulting the Herbarium, Botanical Survey of India (BSI), ERC, Shillong, Meghalaya.
Results and Discussion
The observed Rhododendron wattii is a small tree of about 6-–7.6 m in height (Image 2). The inflorescence is a terminal truss (Image 2); hypogynous and nectar pouches are present at the base of the corolla tube. The corolla has blotches or spots of darker colour, which is a typical feature of rhododendron flowers, and acts as a nectar guide. Leaves are obovate to oblong, apex rounded, apiculate, base rounded, glabrous above, with a sparse whitish felted indumentum beneath. The inflorescence bears 18–25 flowers per truss. The flowers are tubular-campanulate, corolla 6-lobed, pink with darker flecks and purplish basal patches. The stamens are 12 in number and unequal, anther lobes brown and dorsifixed and dehisce by apical pores. The ovary is densely pilose with brownish indumentum. The pollen grains remain in permanent clusters of four to form tetrads, which are held together by viscin threads. The viscin threads play an important role in pollen removal from the anthers and its adhesion to pollinators for accurate pollen delivery to the stigma, increasing pollination efficiency (Hesse et al. 2000). The fruit is a capsule that is oblong, grooved, and dehisce from the top by longitudinal slits (Image 3). The seeds are fusiform and winged, which retain viability for about one year when stored at normal temperature and humidity (Williams et al. 2011). No seedlings were observed in its natural habitat.
Rhododendron wattii is an evergreen plant, and leaf renewal occurs throughout the year (Table 1). It was observed that the same branch did not bear flowers consecutively for two years. The fruits dehisce when still attached to the branch (Image 3). The plant grows on rocky hill slopes with other Rhododendron species R. macabeanum, and dwarf bamboo, mosses, and ferns. The flowers bloom in the last week of February, while peak flowering is observed in the second week of March and declines by the first week of April. Fruit initiation begins in April and matures by the month of December (Table 1). Fruit is a capsule dehiscing laterally, producing numerous seeds that are dispersed by wind. The onset of nectar secretion was observed already at the opening bud stage. The same observation has been made by Chwil & Chmielewska (2009).
The most dominant visitors to R. wattii were the passerine Fire-tailed Sunbird Aethopyga ignicauda (Image 3) followed by bumble bees Bombus spp. (Images 3). The duration of foraging by the Sunbird lasted for 1–2 seconds per flower and 1–7 seconds per flower in the case of bumble bees. Nectar and pollen grains are the main attractants for the floral visitors (Table 2). The nectars are secreted by the nectaries present at the base of the corolla tube. The pollen grains were found attached on the ventral surface of birds’ necks during the foraging, whereas in Bombus spp. they were found on both the dorsal and ventral surfaces of the body. The pollen tetrads are present in lumps and bound with viscin threads to increase pollination efficiency, which is the characteristic feature of the family Ericaceae.
Conclusion
The main pollinators of R. wattii are Fire-tailed Sunbirds Aethopyga ignicauda and bumble bees (Bombus spp.), which forage for nectar and carry pollen. Natural regeneration of the plant species was found to be very low though the plants produce numerous seeds. Pornon & Doche (1995) have also reported that seedling recruitment is poor in many rhododendrons. For successful seedling establishment, the seeds require favourable microsites (Cross 1981; Plocher & Carvell 1987; Kohyama & Grubb 1994). Poor seedling survivability and recruitment failure may be another reason why the population of R. wattii is dwindling, making it highly threatened in its natural habitat, besides natural calamities and anthropogenic factors (Mao & Gogoi 2012; Mao et al. 2018). Thus, there is an urgent need to conserve this species by protecting its natural habitat.
Table 1. Phenology of Rhododendron wattii.
|
Parameters |
Observations (2012–2013) |
|
Leaf fall |
Evergreen |
|
Leaf renewal |
Throughout the year |
|
Flowering period i. Minimum ii. Maximum iii. Decline |
Last week of February The second week of March The first week of April |
|
Initiation of fruits |
April |
|
Fruit maturation |
December |
|
Seed dispersal |
January |
|
Mode of seed dispersal |
Wind |
Table 2. Visitor census in Rhododendron wattii.
|
Order |
Family |
Scientific name |
Common name |
Forage type |
Duration of foraging per flower (in seconds) |
Visiting hours |
|
|
Nectar |
Pollen |
||||||
|
Passeriformes |
Nectariniidae |
Aethopyga ignicauda |
Fire-tailed Sunbird |
+ |
– |
1–2 |
0900–1600 h |
|
Hymenoptera |
Apidae |
Bombus spp. |
Bumble bees |
+ |
– |
1–7 |
1200–1600 h |
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References
Chwil, M. & E. Weryszko-Chmielewska (2009). Characteristics of nectaries and nectar in flowers of two Rhododendron species. Journal of Apicultural Science 53(1): 17–26.
Cross, J.R. (1981). The establishment of Rhododendron ponticum in the Killarney Oakwoods, S.W. Ireland. Journal of Ecology 69: 807–824.
Gibbs, D., D. Chamberlain & G. Argent (2011). The Red List of Rhododendrons. Botanic Gardens Conservation International, Richmond, UK, 128 pp.
Hesse, M., S. Vogel & H. Halbritter (2000). Thread-forming structures in angiosperm anthers: their diverse role in pollination ecology, pp. 281–292. In: Dafni, A., M. Hesse & E. Pacini (eds.). Pollen and Pollination. Springer, Vienna, IX + 341 pp. https://doi.org/10.1007/978-3-7091-6306-1_15
Kohyama, T. & P.J. Grubb (1994). Below and above-ground allometries of shade-tolerant seedlings in a Japanese warm-temperate rain forest. Functional Ecology 8: 229–236.
Ma, Y., J. Nielsen, D.F. Chamberlain, X. Li & W. Sun (2014). The conservation of Rhododendrons is of greater urgency than has been previously acknowledged in China. Biodiversity and Conservation 23: 3149–3154. https://doi.org/10.1007/s10531-014-0764-9
Mainra, A., H.K., Badola & B. Mohanty (eds.) (2010). Proceedings, International Conference, Rhododendrons: Conservation and Sustainable Use, Forest Environment and Wildlife Management Department, Govt. of Sikkim, Gangtok-Sikkim, India, 100 pp.
Mao, A.A. (2010). The genus Rhododendron in north-east India. Botanica Orientalis 7: 26–34. https://doi.org/10.3126/botor.v7i0.4370
Mao, A.A. & R. Gogoi (2007). Rediscovery of a critically endangered endemic Rhododendron. The Indian Forester 133(12): 1699–1702.
Mao, A.A. & R. Gogoi (2012). Rhododendrons of Manipur and Nagaland, India. NeBio 3(1) 1–10.
Mao, A.A., K.P. Singh & P.K. Hajra (2001). Rhododendrons, pp. 2167–2202. In: Singh, N.P. & D.K. Singh (eds.). Floristic Diversity and Conservation Strategies in India. Volume IV: Angiosperms (Selected Groups), Economic and Ethnobotany. Botanical Survey of India, Kolkata, India, 2340 pp.
Mao, A.A., D. Vijayan, N. Rajkumari & S. Pradhan (2018). In vitro propagation of Rhododendron wattii Cowan - a critically endangered and endemic plant from India. In Vitro Cellular & Developmental Biology - Plant 54: 45–53. https://doi.org/10.1007/s11627-017-9869-7
Mao, A.A., S.S. Dash & P. Singh (2017). Rhododendrons of North East India. Botanical Survey of India, Kolkata, 167 pp.
Paul, A., M.L. Khan, A. Arunachalam & K. Arunachalam (2005). Biodiversity and conservation of rhododendrons in Arunachal Pradesh in the Indo-Burma biodiversity hotspot. Current Science 89(4): 623–634.
Plocher, A.E. & K.L. Carvell (1987). Population dynamics of rosebay rhododendron thickets in the southern Appallachians (USA). Bulletin of Torrey Botanical Club 144: 121–126. https://doi.org/10.2307/2996120
Pornon, A. & B. Doche (1996). Age structure and dynamics of Rhododendron ferrugineum L. populations in the northwestern French Alps. Journal of Vegetation Science 7(2): 265–272. https://doi.org/10.2307/3236327
Williams, E.G., J.L. Rouse, B.F. Palser & R.B. Knox (2011). Reproductive Biology of Rhododendrons. In: Janick, J. (ed.). Horticultural Reviews Vol. 12. Timber Press, Portland, Oregon, 68 pp. https://doi.org/10.1002/978118060858