# Light microscopic studies of some pollen morphotypes of the upper montane Nilgiri flora

Jean Lazar, S Prasad, Krishnamurthy Anupama

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Jean Lazar, S Prasad, Krishnamurthy Anupama. Light microscopic studies of some pollen morphotypes of the upper montane Nilgiri flora. 4th Advanced Institute for Wildlife Conservation Annual Research Conference, Advanced Institute for Wildlife Conservation (Research, Training & Education), Tamil Nadu Forest Department, Vandalur, Chennai. © 2025, AIWC, Tamil Nadu Forest Department., Feb 2025, Vandalur, India. pp.214-229. [hal-05461162](https://hal.science/hal-05461162v1)

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<figure><img src="image_1.png" /></figure>
Lazar J, Prasad S and Anupama K 2025 "Light microscopic studies of some pollen morphotypes of the upper montane Nilgiri flora" In: Udhayan, A., Sebagapriya, S., Eswaran, D., Manimozhi, A., Sankar, K., Vasanthakumari, D., Siva Ranjani, S. and Gabriel Paulraj, M. (eds.) *Proceedings of 4th Annual Research Conference*, hosted by Advanced Institute for Wildlife Conservation (Research, Training & Education), Tamil Nadu Forest Department, Vandalur, Chennai, February 13-14, 2025, p214-229. ISBN: 978-81-963181-1-6. Available online at https://www.aiwc.res.in/admin-assets/uploads/handbook/66131.pdf
4th Annual research Conference of the AIWC, Tamil Nadu Forest Department, Vandalur, Chennai,
February 13th & 14th 2025

# Light microscopic studies of some pollen morphotypes of the upper montane Nilgiri flora

*Lazar J, Prasad S and Anupama K

Laboratory of Palynology & Paleoecology, Department of Ecology, French Institute of Pondicherry,
No.11, Saint Louis Street, Puducherry 605001, India.

*Email: lazar.j@ifpindia.org

## ABSTRACT

The study of the microscopic features of the pollen grains, Palynology, provides robust inputs for understanding the flora when combined with the habits and habitats of the plants that yielded them. The present study investigates the pollen morphological features of a selection of 18 of the pollen taxa recovered from six surface soil samples from grasslands in the upper montane region of the Nilgiris, a biodiversity hotspot in the Western Ghats of India, characterized by alternate stable states (forests, grasslands and swamps). Samples were collected during January and March 2024, in the framework of the ongoing Nilgiri Archeological project. This Light Microscopic study focuses on identifying and classifying pollen morphotypes based on the morphological characteristics of the pollen wall, the exine that remains as a proxy of the plant that produced it, contributing to our understanding of the local vegetation and landscape dynamics. The qualitative and quantitative pollen morphological features observed were: aperture type, shape, size and exine ornamentation in a mix of arboreal (Olea glandulifera-t, Meliosma, Dodonaea viscosa, Ilex, Ligustrum, Pinus, Rapanea, Daphniphyllum and Acacia) and non-arboreal pollen taxa (Justicia-t, Apiaceae, Impatiens, Artemisia, Asteraceae (echinate), Asteraceae (fenestrate), Cyperaceae, Gentianaceae and Poaceae). In addition to helping identify the possible plant groups that produced them, the diversity of traits in the pollen morphotypes reflects adaptations of the plants to different ecological conditions providing some insights into pollen biology and their role in plant systematics. Site-specific variations in distribution of the pollen morphotypes within the dataset of surface samples presented are also briefly discussed in view of factors (e.g., edaphic, microclimatic, topographic and anthropogenic) affecting pollen deposition. As pollen remains one of the best-preserved plant proxies in past sedimentary deposits, critical insights into regional pollen morphology holds the key to broader applications such as the interpretation of present and past vegetation structures, foraging preferences of pollinators like native honeybees and other similar applications.

**Keywords:** Pollen traits; climatic changes; palaeoecology; palaeoclimatology; vegetation reconstruction
**Introduction**

Pollen grains function as structures that house the male gametophyte in seed plants. The study of pollen
morphology, termed Palynology, primarily focuses on the structure of the pollen walls rather than their
internal features. The field of pollen analysis originated in 1916 with the investigation of Quaternary
sedimentary deposits from lakes and bogs (Von Post, 1916; Birks and Berglund, 2018). Today, it
remains a crucial tool for reconstructing past vegetation and environmental conditions. Pollen analysis
can also be considered a remote sensing tool, capturing the historical and present composition of
vegetation (Webb et al. 1978; Lazar, 2025). Palynology has demonstrated additionally its value in the
study of taxonomic groups and various scientific disciplines, as well as in a range of Quaternary
applications, including palaeoecology, palaeoclimatology and archaeology (Macdonald, 1988;
Bhagwat et al. 2012; Anupama et al. 2014a, 2014b; Clément et al. 2024). Information obtained from
pollen studies can offer insights into how natural vegetation has responded to human activities
throughout history, as also to climatic and environmental changes (Prentice, 1988; Edwards and
Macdonald, 1991). Pollen grains from various flowers exhibits unique characteristics in terms of shape,
size and surface ornamentation (Wodehouse, 1959; Erdtman, 1966; Nayar, 1990; Tissot et al. 1994)

Pollen grains typically possess apertures, which can be either elongated or circular, with variation in the number of apertures. The apertures may be elongated (colpi) or circular (pores) or a combination of both these (colporus). The apertures are prominent, often interrupting the fine structural patterns on the surface of the pollen grain. Aperture diversity is diverse across different taxa, families, species, and even within individual plants (Mignot et al. 1994). Pollen wall patterns are diverse and often unique to individual species, making them valuable for taxonomic classification and forensic investigations (Szibor et al. 1998). The exine, the outer layer of a living pollen grain, is divided into two distinct sublayers: an inner smooth layer (nexine) and an outer sculptured layer (sexine). The chemically resilient outer layer is primarily composed of sporopollenin—a complex polymer with minor amounts of polysaccharides (Birks and Birks, 1980), resistant to decomposition, and preserved in various substrates like amber, lignite and anaerobic sediments such as peat deposits in both Quaternary and pre Quaternary sequences. The pollen grains of each plant species exhibit distinct features making them valuable for identifying plant species in fossil remains from various deposits and sites.

Detailed pollen descriptions are crucial, as understanding vegetation history relies heavily on pollen analysis. Pollen morphology often plays a significant role in plant taxonomy, often supporting the classification of specific families (eg: Thanikaimoni, 1970 for Arecaceae; Seetharaman, 1985 for Clusiaceae). While taxonomists traditionally rely on phenotypic characteristics to identify plant species, pollen morphology too offers a reliable basis for plant species identification (Punt et al. 2007; Rouhan and Gaudeul, 2021). In this context, while the Nilgiris region is renowned for its diverse range of flowering plants, comprehensive information on the pollen morphology and diversity of pollen taxa is limited (Vasanthy, 1988).

The present Light Microscopic study investigates the pollen morphological features of a selection of 18 of the pollen taxa recovered from six surface soil samples from grasslands in the upper montane region of the Nilgiris, a biodiversity hotspot in the Western Ghats of India. The six surface samples were collected between January and April 2024 in the framework of the ongoing Nilgiri Archeological project and their pollen content was extracted and examined under a Light Microscope. The focus is on identifying and classifying pollen morphotypes based on the morphological characteristics of the pollen. This was done in 18 out of a total of 45 pollen taxa found in the six surface sediments. The qualitative and quantitative pollen morphological features observed included aperture type, shape, size and exine ornamentation in a mix of arboreal (AP) and non-arboreal (NAP) pollen including some introduced plants such as *Pinus* and *Acacia* that currently dominate these landscapes (Table 1).
# MATERIALS AND METHODS

## Study area and Sampling

Sampling was carried out across multiple locations in Nilgiris, namely Tenth Mile (11°27'31.30"N; 76°37'11.40"E), Taranadu Mund (11°29'30.10"N; 76°37'12.30"E), Aduthal Mund (11°29'10.10"N; 76°37'12.80"E), Muthanad Mund (11°26'51.80"N; 76°39'52.80"E), Seventh Mile (11°26'35.30"N; 76°38'19.10"E) and Ninth Mile (11°26'17.20"N; 76°37'44.00"E) (Fig. 1). These montane sites consist of alternate stable states (shola forests, grasslands and swamps) interspersed with plantations, primarily managed by the Toda community. The vegetation comprises a mix of native (shola forest trees like *Ilex denticulata*, *Daphniphyllum neilgherrense*, *Michelia nilagirica*; different grass species of *Sisyrinchium*, *Eragrostis*, *Apluda*, and in limited pockets, *Eriochrysis rangachari* called "Avvul" by the Todas who favour it for the construction of their traditional roof; different species of sedges like *Cyperus* and *Fimbrystylis* and swamp elements such as different species of *Impatiens*, *Eriocaulon* and *Xyris*.) and introduced and invasive taxa (like *Acacia* spp., *Eucalyptus* sp., and *Cestrum elegans*). Surface soil samples were collected from six distinct locations within grasslands with patches of remnant sholas overlapping within a radius of 1 km around the points of surface soil collection during the period of January and March 2024. The present landscape is characterized by an interruption of the natural grasslands and marshlands with patches of trees and shrubs that have invaded it.

## Sample preparation and microscopic analysis

The six surface soil samples collected as mentioned above were analyzed for their pollen content at the Laboratory of Palynology, French Institute of Pondicherry (IFP). To process the samples, after removal of silicates using 40% HF, acetolysis method (Erdtman, 1960) was followed to eliminate cellulose and other cellular materials obscuring the visibility of exine. For morphological examination, the acetolyzed pollen grains were mounted on glass slides using glycerin, covered with cover slips and sealed with DPX mountant. Light microscopy (LM) was conducted using an Olympus microscope with a ×40 objective lens, while a ×100 objective was employed for detailed pollen identification, and images were captured using relevant software installed with camera attachment. Each pollen grain was systematically examined, and key morphological traits including aperture type, shape, size and surface ornamentation were observed using reference collection and literatures (Faegri and Iversen, 1989). The size ranges and descriptions for the pollen morphotypes provided here are based on cross-checking with the appropriate reference pollen slides and then incorporating this knowledge in the studied samples. It also draws on measurements made on the same pollen taxa reported in other modern surface and quaternary studies (e.g., Anupama et al., 2014a; Navya, 2020). It is of note that the list of selected pollen taxa comprises a mixed taxonomic hierarchy with *Dodonaea viscosa* at the species level and taxa like Poaceae and Cyperaceae at the family level; there are also pollen types such as *Justicia*-t (Anupama et al, 2014a) and *Olea glandulifera*-t that may include members of other genera in Oleaceae like *Chionanthus* spp. in a different landscape.
<figure><img src="image_2.png" /><figcaption>**Fig 1.** Location map of the study areas in Nilgiris (Source: Google Maps).</figcaption></figure>
## Results

A total of 45 distinct pollen taxa were identified during the light microscopic study of the six surface samples collected and analyzed as detailed above of which 20 were arboreal 23 non arboreal, one (Croton-t) was non-classified, and one remained unidentified (Figure 2). Among the dominant plant taxa, Poaceae was the most prevalent, followed by Cyperaceae, Asteraceae (both echinate and fenestrate types), Gentianaceae, Apiaceae and Olea glandulifera-t, which were recorded in all study sites (Fig. 2). Most other taxa, such as Artemisia, Justicia-t, Meliosma, Dodonaea viscosa, and introduced taxa like Eucalyptus, Acacia and Pinus, appeared less frequently in the soil pollen assemblages. Certain pollen taxa showed site-specific prominence or occurences: Impatiens was recorded only at Aduthal Mund where Ilex was more seen; Artemisia appears only in both Aduthal Mund and Seventh Mile; Acacia and Pinus reach their respective maximum only in Tenth Mile; Gentianaceae was recorded in more numbers at Seventh Mile and Muthanadu Mandu.

For the detailed microscopic and morphological examination 18 pollen taxa highlighted by asterisks were selected to reflect the regional diversity of pollen morphotypes. The qualitative and quantitative pollen morphological features observed included aperture type, shape, size and exine ornamentation in a mix of 9 arboreal (AP) and 9 non arboreal pollen (NAP) (Table 1). Among the selected pollen taxa, three are from the Asteraceae family (Asteraceae (echinate) and Asteraceae (fenestrate) types; and Artemisia), and two are from Oleaceae (Olea glandulifera-t and Ligustrum). Others comprise taxa such as Justicia-t, Acacia, Meliosma, Dodonaea viscosa, Rapanea, Impatiens, Daphniphyllum, Poaceae, Cyperaceae, Gentianaceae, Apiaceae Pinus and Ilex that are distinct morphotypes from 13 distinct families (Table 1; Plates 1a, b).

Pollen morphology of the selected morphotypes (Plate 1a, b) exhibited variations across different plant species, displaying a wide range of characteristics related to exine ornamentation patterns, shape, size and aperture type. The majority of species produced pollen grains dispersed as monads, except for Acacia, which exhibited polyads. Shape diversity was also evident, with prolate, spheroidal, and oblate spheroidal forms being the most commonly observed. Apiaceae and Justicia-t pollen were primarily prolate, while Artemisia, Asteraceae (echinate) displayed a variety of forms, including prolate spheroidal, spheroidal and oblate spheroidal. Pollen from Poaceae and Asteraceae (fenestrate) were mostly spheroidal. Other distinct morphologies included bisaccate grains in Pinus (Plate 1b (F)), spheroidal-obovoid in Cyperaceae (Plate 1a (H)), and oblate grains with a rectangular polar view in Impatiens (Plate 1a (D)). The dataset reveals a range of pollen sizes, with the size of the pollen axes varying across pollen morphotypes. The smallest pollen size ranges (~20-30 µm P, 18-22 µm E) among the chosen taxa were for Asteraceae (echinate) and Justicia-t, while Pinus has the largest pollen grains (65-80 µm P, 35-45 µm E), with bisaccate units that enhance wind dispersal. In contrast, Poaceae (grass) produce spheroidal pollen (38-42 µm P, 40-45 µm E), featuring a psilate surface and monoporate apertural condition.

Aperture types vary among the studied pollen grains. Poaceae exhibits monoporate condition (Plate 1b (G)), while Cyperaceae has 4-5 apertures (Plate 1a (H)). Impatiens displayed 4-5 colpate apertures (Plate 1a (D)). Composite aperture types were frequently recorded, with eight taxa—such as Gentianaceae, Ilex, and Dodonaea viscosa—showing 3-colporate pollen grains (Plate 1b (I)), while Rapanea had 4-colporate grains (Plate 1b (C)). Exine sculpture (ornamentation) also exhibited significant diversity. Reticulate exine was observed in six taxa, including Apiaceae, Ligustrum and Olea glandulifera-t. Striato-reticulate ornamentation was observed in Gentianaceae, while granulate exine was characteristic of Daphniphyllum and Dodonaea viscosa. This study shows that species from the family Asteraceae exhibited echinate (and microechinate), and fenestrate exine patterns. Additionally, clavate-type ornamentation was recorded in Ilex, while a generally psilate exine was observed in both Poaceae and Cyperaceae. Pollen grains from the family Pinaceae (Pinus) were found
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Frequency of occurrence of various pollen taxa (all 45 taxa/types excluding spores) retrieved from surface soil samples of six sites in the Nilgiris. The selected 18 pollen taxa are highlighted with asterisk (*).</figcaption></figure>

Sites: ADM - Aduthal Mund, TM - Tenth mile, TNM - Taranad mund, NM - Ninth mile, SM - Seventh mile, MM - Muthnad mund
<table><caption>**Table. 1** Morphological characters of selective (18) pollen taxa/traits chosen from various study sites at Nilgiris.</caption><thead><tr><th>Sl.No</th><th>Family</th><th>Pollen Taxa</th><th>Group</th><th>Size µm (P)</th><th>Size µm (E)</th><th>Shape</th><th>Ornamentation</th><th>Aperture</th></tr></thead><tbody><tr><td>1</td><td>Acanthaceae</td><td>Justicia-t</td><td>NAP</td><td>25-30</td><td>18-20</td><td>Prolate</td><td>Reticulate</td><td>3 Colporate/porate</td></tr><tr><td>2</td><td>Apiaceae</td><td>Apiaceae</td><td>NAP</td><td>40-45</td><td>15-18</td><td>Prolate</td><td>Reticulate</td><td>3 Colporate</td></tr><tr><td>3</td><td>Aquifoliaceae</td><td>Ilex</td><td>AP</td><td>30-35</td><td>22-25</td><td>Prolate</td><td>Clavate</td><td>3 Colporate</td></tr><tr><td>4</td><td>Balsaminaceae</td><td>Impatiens</td><td>NAP</td><td>15-22</td><td>25-35</td><td>oblate (Rectangular in polar view)</td><td>Reticulate</td><td>4 to 5 colporate</td></tr><tr><td>5</td><td>Asteraceae</td><td>Artemisia</td><td>NAP</td><td>20-28</td><td>15-25</td><td>Prolate spheroidal/ spheroidal/ oblate spheroidal</td><td>Microechinate</td><td>3 Colporate</td></tr><tr><td>6</td><td>Asteraceae</td><td>Asteraceae (echinate)</td><td>NAP</td><td>20-25</td><td>18-22</td><td>Prolate spheroidal/ spheroidal/ oblate spheroidal</td><td>Echinate</td><td>3 Colporate</td></tr><tr><td>7</td><td>Asteraceae</td><td>Asteraceae (fenestrate)</td><td>NAP</td><td>20-25</td><td>20-25</td><td>Spheroidal</td><td>Fenestrate</td><td>3 Colporate</td></tr><tr><td>8</td><td>Cyperaceae</td><td>Cyperaceae</td><td>NAP</td><td>28-40</td><td>25-35</td><td>Spheroidal-obovoid</td><td>Psilate</td><td>4 to 5 faintly aperturate</td></tr><tr><td>9</td><td>Euphorbiaceae</td><td>Daphniphyllum</td><td>AP</td><td>23-25</td><td>23-25</td><td>Prolate spheroidal/ spheroidal/ oblate spheroidal</td><td>Granulate</td><td>3 colporoidate</td></tr><tr><td>10</td><td>Gentianaceae</td><td>Gentianaceae</td><td>NAP</td><td>40-45</td><td>25-30</td><td>Prolate/ prolate spheroidal</td><td>Striato-reticulate</td><td>3 Colporate</td></tr><tr><td>11</td><td>Mimosaceae</td><td>Acacia</td><td>AP</td><td>40-42</td><td>35-38</td><td>Prolate/ prolate spheroidal (for the polyad)</td><td>Polyads</td><td>Polyaperturate</td></tr><tr><td>12</td><td>Myrsinaceae</td><td>Rapanea</td><td>AP</td><td>25-28</td><td>20-22</td><td>Prolate spheroidal/ Spheroidal</td><td>Granulate/Psilate</td><td>4 colporate</td></tr><tr><td>13</td><td>Oleaceae</td><td>Ligustrum</td><td>AP</td><td>30-35</td><td>25-30</td><td>Prolate spheroidal/ spheroidal/ oblate spheroidal</td><td>Reticulate</td><td>3 Colporoidate</td></tr><tr><td>14</td><td>Oleaceae</td><td>Olea glandulifera-t</td><td>AP</td><td>25-28</td><td>25-28</td><td>Prolate spheroidal/ spheroidal/ oblate spheroidal</td><td>Reticulate</td><td>4 Colporoidate</td></tr><tr><td>15</td><td>Pinaceae</td><td>Pinus</td><td>AP</td><td>65-80 (L)</td><td>35-45 (W)</td><td>Disaccate</td><td>Reticulate-granulate</td><td>Inaperturate</td></tr><tr><td>16</td><td>Poaceae</td><td>Poaceae</td><td>NAP</td><td>38-42</td><td>40-45</td><td>Spheroidal</td><td>Psilate</td><td>Monoporate</td></tr><tr><td>17</td><td>Sabiaceae</td><td>Meliosma</td><td>AP</td><td>35-40</td><td>35-38</td><td>Prolate-spheroidal</td><td>Reticulate</td><td>3 Colporate</td></tr><tr><td>18</td><td>Sapindaceae</td><td>Dodonaea viscosa</td><td>AP</td><td>35-40</td><td>33-36</td><td>Prolate spheroidal/ spheroidal/ oblate spheroidal</td><td>Granulate</td><td>3 Colporate</td></tr></tbody></table>
to be inaperturate with a unique bisaccate structure with a reticulate-granulate texture (Plate 1b (F)).
To gain a comprehensive understanding of the different pollen types within a family, it is crucial to
analyze a large number of pollen grains, across different genera; species level identification using
only LM is rare but feasible, as with *Dodonaea viscosa* in this study.

**Discussion**

This study describes the pollen morphology of 18 pollen taxa from 15 families revealing variations in the nature and number of apertures, exine sculpturings, shapes and size. Among the identified pollen taxa, Poaceae and Cyperaceae were the most frequently occurring across all analyzed samples (Fig. 2). Certain pollen taxa, even when present in low frequencies, hold ecological significance as indicators of shola forest ecosystems. For instance, the genera *Ilex*, *Ligustrum*, *Rapanea* and *Impatiens* are commonly associated with hygrophilous environments and montane forests and we find their corresponding pollen taxa in most of the studied sites. Pollen from the Apiaceae family are generally linked to cultivated vegetation, but in this landscape they are found mainly in the grasslands and frequently considered a relative “dryness” indicator along with other taxa like *Artemisia* (Sutra et al. 1997).

Similarly, site-specific variations in pollen distribution such as the rare occurrence of *Impatiens* in only one site or the differences in proportions of Cyperaceae, Poaceae, *Artemisia* and Gentianaceae. *Pinus* and *Acacia* observed in this study suggest the potential influence of edaphic microclimatic topographic and anthropogenic factors on pollen deposition, which is crucial for accurately reconstructing past vegetation dynamics and assessing anthropogenic impacts on regional flora. Among these, it is of note that though introduced species of *Pinus* and *Acacia* (known to be invasive: Hiremath and Sundaram 2013) dominate this montane landscape currently, both in their sheer numbers and in their size too, neither taxon nor others such as *Eucalyptus* (not discussed here for morphology but included in Fig. 2) ever reach percentages over five. The case of low proportions of *Pinus* in our samples (only notable presence is at Tenth Mile – see Fig 2) is intriguing in terms of its morphology. *Pinus* is a winged pollen and known to be transported over very long distances but its record again like *Acacia* is found in very small percentages. While pollen of *Acacia* are considered to be mostly entomophilous they have also been reported in surface samples elsewhere in India (Navya, 2020) and in Africa (Gaillard et al. 2021). The advantage in this landscape for these introduced invasives is that they are able to tower over the native shola trees with the ability to disperse both pollen and seeds into the grasslands. Though preliminary, our finding that the pollen dispersal of these two species in the grassland samples seems limited could have implications for better managing the eradication of these species based on their dispersal mechanism.

As noted by Carvalho et al. (1999), species present with less than 1% may be due to limited pollen
production, as observed in *Justicia*-t, *Daphniphyllum* and *Impatiens*. Some samples contained
unidentified pollen taxa, highlighting challenges in determining the botanical origin of certain pollen
grains. This difficulty is often attributed to gaps in our understanding of the pollen of the regional flora.
Furthermore, pollen grains from distinct plant families may exhibit morphological similarities, as seen
in the common tricolporate, reticulate pollen taxa that are prevalent among dicotyledons.

Identifying pollen from soil samples can provide valuable insights into local and regional scale
botanical composition even without extensive vegetation surveys. The present study shows that as
many as 45 pollen taxa were recovered from only six study sites and that most of them correspond to
the native shola grasslands and swamp formations found here as alternate stable states of vegetation.
Work is ongoing in this project to extend the pollen morphological study to key montane forest taxa in
the Nilgiris by continuing to collect both surface samples, sediment cores and whenever available pollen from native honeybee combs found nesting in tree hollows (Appendix 1).

<figure><img src="image_4.png" /><figcaption>**Plate 1a.** LM images of some of the pollen taxa from the Nilgiris. A. *Justicia*-t, B. Apiaceae, C. *Ilex*, D. *Impatiens*, E. *Artemisia*, F. Asteraceae (echinate), G. Asteraceae (fenestrate), H. Cyperaceae, I. *Daphniphyllum*</figcaption></figure>

Scale bar: 10 µm
<figure><img src="image_5.png" /><figcaption>**Plate 1b.** LM images of some of the pollen taxa from the Nilgiris. A. Gentianaceae, B. *Acacia*, C. *Rapanea*, D. *Ligustrum*, E. *Olea glandulifera*–t, F. *Pinus*, G. Poaceae, H. *Meliosma*, I. *Dodonaea viscosa*.</figcaption></figure>

Scale bar: 10 µm
## Conclusions

The first results from this ongoing study are promising in at least three ways: 1) they establish the capability of pollen analysis to serve as a potential remote sensing tool capturing a large assemblage of the native vegetation in this complex landscape even without a vegetation survey though such surveys are essential in the perspective to establish quantitative pollen-vegetation relationships here; 2) they provide tangible evidence that at least some of the introduced and invasive taxa (*Pinus* and *Acacia*) that currently overpower this montane landscape are not significant from a palynological angle providing an impetus to further research on their dispersal mechanism (Appendix 1) and subsequently their management and 3) the palynological imprint of the native vegetation reflecting much of its diversity even when recorded in lower proportions as distinctly identifiable morphotypes. These results are a direct consequence of an accurate identification of the regional pollen morphotypes emphasizing the need for more in-depth pollen morphological studies in this montane region with a complex vegetation distribution. Such pollen morphological studies can also yield additional valuable insights for taxonomic classification, while also contributing to phylogenetic studies that can help make the link with both the evolutionary and the environmental factors responsible. The dominance of tricolporate apertures in dicotyledons (eg: *Dodonaea viscosa*, Asteraceae (echinate), *Olea glandulifera*-t), monoporate and faint apertures in monocotyledons (Poaceae; Cyperaceae) align with established taxonomic patterns. These findings highlight the importance of pollen characteristics in plant taxonomy and evolutionary research, emphasizing their role in understanding species relationships and adaptations.

## Acknowledgements

We thank the Forest Department of Tamil Nadu for providing the necessary permissions (Permission Number 27/2023 and Proceeding number WL5(A)/38365/2023 dated 18/04/23 from the PCCF and Wildlife Warden; Proceedings of the Deputy Director, Mudumalai Tiger Reserve, Udhagamandalam; Reference No. 2880/2023-T) and granting field support at the study sites during our surveys. This research was undertaken as part of the *Nilgiri Archaeological Project* (2021–2026), funded by an Odysseus II grant (no. G0F0621N) awarded by the Research Foundation–Flanders (FWO). All the laboratory and microscopic infrastructure used in these analyses as well as the Thanikaimoni pollen slides reference collection were facilitated at the French Institute of Pondicherry that hosts the paleoecological component of this project. We thank the PI of the Nilgiri Archaeological Project Dr. Daniela De Simone, at Ghent University, Belgium who has been very supportive throughout and encouraged both the presentation and this publication. The field assistance of Mr. Puthu Raja (Toda) from Taranad Mund, Nilgiris, is highly appreciated.

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