Studies on the phenology of some terrestrial orchids of Western Ghats, India

The present paper describes the distribution, natural habitat and phenology of some terrestrial orchids in Shimoga district, Karnataka. The phenophases viz., leafing, flowering, fruiting, fruit dehiscence are observed for 25 orchid taxa belonging to 13 genera in Shimoga district. They are Dienia ophrydis (J. Koenig) Seidenf. , Disperis zeylanica Trimen., Epipogium roseum (D. Don) Lindl ., Eulophia spectabilis (Dennst.) Suresh. , Geodorum densiflorum (Lam.) Schltr. , Habenaria crinifera Lindl. , Habenaria elwesii Hook f ., Habenaria furcifera Lindl., Habenaria grandifloriformis Blatt. & Mc Cann. , Habenaria heyneana Lindl ., Habenaria longicorniculata J. Graham. , Habenaria multicaudata Sedgw., Habenaria plantaginea Lindl. , Liparis deflexa Hook. f., Liparis odorata (Willd) Lindl ., Malaxis versicolor ( Lindl.) Abeyw. , Nervilia concolor (Blume) Schltr. Nervilia crociformis (Zoll. & Moritzi) Seidenf ., Nervilia infundibulifolia Blatt. & Mc Cann. , Nervilia plicata (Andrews) Schltr. , Pecteilis gigantea (Sm.) Phenology is the timing of plant life cycle events. Regular field visits were carried to observe the different life events. Most of the terrestrial orchids complete their life cycle in April to September or October month. The present research gives additional phenological aspects of terrestrial orchids in Shimoga district. Vegetative phenology is important to understand the ecology and instinct history of a plant species and may help to develop the conservation strategies of endangered species.


Introduction
The Orchidaceae is one of the largest families of flowering plants represented by 25000-35000 species distributed in 600-800 genera in the world (1). In India, Orchidaceae is represented by about 152 genera and 1300 species (2), in which 84 species in 30 genera are endemic to Western Ghats (3). Family Orchidaceae in the state of Karnataka is represented by 203 species belonging to 59 genera, of which 17 species are terrestrial orchids in Shimoga district (4). The Biodiversity rich Western Ghats represents 300 species out of which 84 species under 30 genera are endemic and 15 species are endangered (5).
The orchid plants show the wide distribution in varied, climatic, edaphic, topographical situations and proved their successful adaptability. Orchids are attracting the plant explorers and taxonomic workers in Karnataka (6)(7)(8)(9). Observations were also on 15 terrestrial orchids in Shimoga district (10).
Orchids are mainly categorized into two types terrestrial and epiphytic forms, terrestrial orchids grow on the ground while epiphytic ones grow on tree trunks or other substratum. Usually almost all orchids are associated with endophytic symbiotic fungus mainly in their roots. The terrestrial forms include those which inhabit the forest floor that is they grow under the shady environment. Terrestrial orchid are found to grow in various forest types such as scrub jungles, dry deciduous forests, moist deciduous forests, semi-evergreen as well as in evergreen forests. Orchids are distributed from sea level 1500 m altitudes with rainfall ranging from 60-300 cm. The maximum numbers of terrestrial orchids are found in evergreen and semi-evergreen forests of the Western Ghats.
Plant phenology is the timing of major events in the life history of the plant with reference to seasons (11,12). The phenology study deals not only the vegetative and reproductive phase corresponding to the climate and seasonal changes of a particular area but also determines the degree of reproductive synchrony with other plant species (10,13). The phenology is a key tool for the plant management, conservation of species, floral biology, estimation of reproductivity and regeneration (14,17). Flowering phenology is one of the most important characteristics in the life history of plants because it strongly determines fitness through sexual reproduction (10)(11)(12)(13). The phenological studies  mainly reflect the occurrence of plants in response to  the environment, which include both vegetative and  reproductive stages such as tuber formation, leaf  flushing and shedding, bud formation, flowering,  fruiting,  dehiscence  and  seed germination. Phenological studies are mainly depending on the observation of life cycle events occurring at a given location over a time scale of several years. Both external and internal factors govern the plant phenology. Internal inherited factors are the cause of development of a species and it determines the phenological character even it grows in different climatic conditions. External factor alters the internal factors of the plants. External factors include temperature, rainfall, soil character, humidity, light intensity, altitude etc. Mainly three environment factors which trigger the phenological progress of the plant have been identified usually viz., photoperiod, temperature and moisture (10,13,15). In the present study, detailed phenological studies including the vegetative and reproductive character of terrestrial orchid species were done from different talukas of Shimoga district, Karnataka. Phenological study helps to understand strategies of the species in a particular type of ecosystem. It is also important to understand the ecology and instinct history of a species which in turn help to develop the conservation strategies of rare, endemic and endangered species. Therefore, it is necessary to study the phenology of different taxa for the analysis of reproductive biological aspects.

Materials and Methods
The present work is mainly based on a taxonomic survey in the different forest types of Shimoga district those are evergreen, semi-evergreen, moist and dry deciduous forests and scrub forests in a district during the year January 2018 -January 2021. Collections were made from 7 talukas of Shimoga district. The coordinates of Shimoga district are at 13.9167 0 North, 75.5667 0 East and mean elevation of 640 m above sea level (NRDMS Centre Z. P Office Shimoga) (Fig. 1 Peristylus plantagines (Lindl.), P. spiralis A. Rich., Satyrium nepalense D. Don, Zeuxine longilabris (Lindl.) Trimen. Specimens were identified with the help of regional floras and monographs on Orchidaceae (4,10,18). Necessary photographs were also taken during field visits. The plants are collected from their natural habitats and maintained in the net house for further observation. Parameters are categorized into two parts vegetative and reproductive characters. Measurements were taken with the help of a scale or ruler. The numbers of flowers were counted from 5 plants and average values are recorded. Detailed studies of both categories were made from healthy plant species. Herbarium was prepared as described (20). The specimens are deposited in the herbarium, Department of Botany, Sahyadri Science College, Shimoga, Karnataka, India.

Results and Discussion
It is observed that rain plays a major role in the growth and development of most of the terrestrial orchid species. Terrestrial orchids start to produce leafy shoots at the onset of rainy season. Terrestrial forms absorb their nutrition directly from the soil through the roots. In terrestrial species mainly three kinds of roots are present, (1) one adapted to absorption and fixation. (2) Tuber adapted to nutritive substance storage. (3) One specialized in storage, absorption and fixation (16). Plant tubers have a capacity to survive in the dry season and nourish the plant till the emergence of necessary or favourable conditions and produce new shoots in the upcoming rainy season. Majority of the terrestrial orchids possess rhizome and some have tuber, size and shape of the rhizome vary from species to species. Rhizome has small nodes and internodes and stores plenty of reserve food material, which helps to withstand in dry condition. Malaxis versicolor (Fig. 2  A) shows runner type of modification with pseudobulbs and has nodes and internodes. In this plant young shoots produces at the nodal region. The emergence of new shoots in respect to time varies among the species. It is observed that the maximum number of species sprout out new shoots in the month of April to August. Species like Liparis deflexa, L. odorata and Malaxis versicolor sprout their shoots in February -March. During the present study, it is found that a warm to high temperature with sufficient rainfall and moisture favour the sprout of new shoots in most of the species. In terrestrial orchids, stems exhibit variations in their shape and size ranging from short slender to thick and fleshy, erect and covered with leaf sheaths. The height of the stem varies from species to species. Maximum stem height is observed in Pecteilis gigantea (450 mm) smallest in Habenaria grandifloriformis (23 mm), and Nervilia crociformis (40 mm). Leaves in terrestrial orchids conform to the monocotyledons pattern. In terrestrial forms, leaf is long and plicate or short cordate, elliptic, oblong, linear, ovate shape is also observed. Longest leaf is observed in Geodorum densiflorum (145 mm) (Fig. 2, K) and shortest in Habenaria grandifloriformis (17 mm). Highly thick short leaf is observed in Habenaria grandifloriformis (Fig. 2, B), (Table 1).
In terrestrial forms, the inflorescence is terminal only. Mainly inflorescence is produced from a leafy shoot but in few cases like Nervilia crociformis, N. plicata, N. concolor, flowers bloom first later on single leaf develops. The Inflorescence is in simple or compound racemes. In N. crociformis and N. infundibulifolia inflorescence are single-flowered. The length of the inflorescence varies from one species to another. A maximum length of the inflorescence is found in Pecteilis gigantea (350-470 mm). Whereas minimum in Nervilia crociformis (25-30 mm). The size of flowers varies among different species. The flower shows a variety of colours viz., white, yellow, pinkishwhite, purplish-white among the species studied ( Table 2). Majority of the species initiate flowering buds during the month of June-July with the start of the rainfall. In the case of Nervilia spp. flowers develop from the month of March to April. The flower peak was recorded during the rainy season in the month of July to October.
The number of flower per inflorescence varies from species to species and is related to the length of the inflorescence. The number of flower in inflorescence varies from single to many. Single flower is observed in Nervilia crociformis and N. infundibulifolia ( Table 2). Most of the inflorescence is raceme type; some are spike type. Maximum peduncle length recorded in Pecteilis gigantea during the study.
The different parts such as the sepals, petals and the labellum largely contribute to the beauty of a flower. The sepals and petals show variations from species to species with respect to shape, size and colour ( Table 3). The petals are more pronounced in colour than the sepals and different in size. It is revealing that the greater the length and breadth ratio found in Pecteilis gigantea, and shorter as found in all Malaxis and Liparis spp. studied. The labellum is the most prominent of all perianth parts, with a different shade in colour, shape and size (Table 3). This is the most attractive parts of the flower of an orchid and well displayed by all the studied species. The length of labellum varies from one species to another and recorded maximum in Pecteilis gigantea, the minimum labellum length is observed in Malaxis versicolor (3 mm) (Fig. 2, A).
Terrestrial orchid species usually spend a major portion of the life cycle in the vegetative phase. The initiation of flower in the month of June marks the beginning of the reproductive phase of their life cycle. After full blooming in August -September, growth of the flower-bearing offshoot ceases and pod matures in August -October (Fig. 3). Some species like Nervilia plicata (Fig. 2, H) shed their seeds in April -May and Habenaria. grandifloriformis (Fig. 2, B) produce seeds in April -August (Table 4). The chief mode of propagation in most of the species is from the rhizome which develops during May -June. A strong seasonality exists with respect to vegetative and reproductive phenology in terrestrial forms.
Increase or decrease of the day length, temperature, pre-monsoon and post-monsoon, dry period all these are responsible for leaf formation and maturation. The highest flowering peak was recorded during monsoon in July -September, ripening of the majority of fruits in August -October month. The process of fruit formation, maturation, retention, dehiscence was found to be the longest phenophase in all the species. The difference in the phenological events among the species, majority of the species shows bursting of the seed pod during the month of August-October, dehiscence of seed pod occurs during the same or subsequent month of bursting in all the species, which provides a better chance of dispersal of seeds by a strong wind. Seeds are very minute, the colour of the seeds varies from white to brown. All the seed pod breaks in a single longitudinal slit at first and gradually two to three additional slits develop facilitating wind dispersal. Fruiting stage represented long term phenology records than leaf and flower phenology (19).

Conclusion
Phenology is the study of the timing of recurring biological events, among phases of the plant species, which provides background for collecting and synthesizing detailed quantitative information on the rhythms of plant communities. It is important to study the phenology of a plant so as to give a complete understanding of their morphology, structure and forms for various developments and its management in scientific study. The phenological