INTRODUCTION Sandalwood, Santalum album L. belongs to the family Santalaceae known for its fragrant wood and scented oil (Rocha et al., 2017). It is hemi root parasitic tree partially relying on its host to take water and nutrients (Francis et al., 2019). Sandalwood is indigenous to India covering an area of 9600 Km2 (Gairola et al., 2007), mostly grown in states like Karnataka and Tamil Nadu (Kumar et al., 2012, Kausar et al., 2014, Rocha et al., 2017). Isolated populations of S. album grow in various states of India such as Bihar, Gujrat, Haryana, Maharashtra, Madhya Pradesh, Orrisa, Punjab, Rajasthan, Uttar Pradesh, West Bengal, Assam and Himachal Pradesh. The ecology, growth and host preferences of S. album has been well documented (Zhang et al., 2012, Lu et al., 2013, Yang et al., 2014, Rocha et al., 2017, Lu et al., 2014, Doddabasawa et al., 2020, Doddabasawa and Chittapur 2021). Different researchers have studied the physiology of root parasitism in both pots as well as field/natural populations and observed the interaction between hemi parasitic S. album and different host species. The host-dependent physiology of S. album in association with N2-fixing and non N2-fixing plant species revealed the preference of mixed plantation of S. album with Dalbergia odorifera, a potential N2-fixing host species (Lu et al., 2014). Further, S. album is also specific in choosing compatible host partners. S. album is known as parasite of more than 300 species from trees to grasses known to form haustoria (Rocha et al., 2017, Nagaveni and Vijayalakshmi 2007). One of the population dynamics studies in S. album populations of Himachal Pradesh revealed Lantana camara as dominant associated shrub species. Lantana camara L. is a noxious alien weed belonging to family Verbenaceae. This invasive weed is mostly native to subtropical and tropical America was initially brought to India in 1807 to the National Botanical Garden as an ornamental plant (Kohli et al., 2006, Negi et al., 2019). L. camara is reported to intrude forests of Himalayan Foothills, where it has virtually replaced the forest floor vegetation and reduced trees growth (Negi and Kandpal 2003). The infestations of L. camara are very persistent and have the potential to block succession and displace native species also compete with native colonizers and can interrupt the regeneration process of the other indigenous species. In sub-temperate, sub-tropical and tropical forests this shrub is mainly associated with Acacia catechu, Dalbergia sissoo, Pinus roxburghii and Tectona grandis (Ray and Ray 2014). Li (2016) and Teixeira da Silva et al. (2016) suggested that along with other tree species like Acacia auriculiformis, Acacia confuse, Albizia lebback and Cajanaus cajan, Lantana camara can be a suitable host for S. album in China. Nevertheless, to the best of our knowledge too little or no information is available to support these findings in Indian context. Therefore, a survey was conducted in three districts of Himachal Pradesh to find out the parasitism ecology of S. album under natural population with shrub weed L. camara to address the following questions, 1) Does S. album actually parasitize the L. camara (host) with specialized absorbing structure called haustorium? and 2) Does the haustoria of S. album penetrate host epidermis and cortex establishing a true connection between them? Identifying and understanding the association between both these species would yield important clues on the theoretical and practical significance for encouraging the plantation of economically important S. album tree to meet out its long-term host (secondary host) requirement in lands which are so far invaded by L. camara and further where there is no/minimum possibility of growing any other crop or tree species. MATERIALS AND METHODS The survey was carried out in the year 2021‒2022 at three regions namely, Kangra (latitude 31° 41’ 00” N and longitude 75° 35’ 34” E), Bilaspur (latitude 31°18’00” N and longitude 75°55’00” E) and Hamirpur (latitude 31° 41' 26.8188'' N and longitude 76° 31' 3.7740'' E), Himachal Pradesh, India where Santalum album was recorded as a major tree species growing closely in association with weed shrub species L. camara (Fig. 1A and 1 B). These regions fall in sub-tropical, low hill zone of the state distributed along an altitudinal gradient of 500-700 mamsl with average annual rainfall of 1000-1400 mm. The soils of the surveyed area are characterized as slightly acidic having sandy loam to clay loam texture. The aim of the investigation was to confirm the presence of hautsorial connections between S. album and L. camara growing together. From all the 3 surveyed sites, 20 mature trees of S. album having average girth of 30 cm were randomly selected at a minimum distance of 100 m from each other. Further, 5 mature plants of L. camara at a minimum distance of 2 m and maximum 5 m in radius of each selected S. album tree were excavated with the help of spade and uprooted for further examination. The haustorial associations present on roots of selected L. camara plants were carefully observed and 10 established haustoria on primary, secondary and tertiary roots of each selected host (L. camara) along with host roots were harvested for further anatomical examination. Host roots along with haustoria were wash clean of soil and thin microscopic sections (Longitudinal section) were taken out by following standard procedures of fixing. These sections were examined and images were captured using Fluorescent microscope. Figures were assembled using Microsoft Office Publishers. RESULTS AND DISCUSSION The established haustoria of S. album on L. camara roots were observed in all of the regions surveyed (Fig. 1C). The S. album haustoria were seen attached to primary, secondary as well as tertiary roots of L. camara (Fig. 1, D-F). The presence of haustoria in the host roots indicated the possibility of translocation of water and nutrients from L. camara to S. album. The average number of haustoria host-1 roots were recorded in the range of 50‒100. Maximum number of haustoria were recorded in tertiary roots as compared to the primary and secondary roots. This may be due to the fact that main root playing comparatively lesser role in the absorption of water and nutrients in plants (Daddabasawa and Chittapur 2021). Newly initiated haustoria of S. album were bell-shaped, tapering proximally by a narrow stalk joining onto its parent root. When the initial haustoria come in contact with compatible host roots they flatten against the surface and initiate the transition into the young haustoria. For the first time we investigated the anatomy of S. album haustoria attached to roots of noxious weed L. camara and noticed the close vascular connection between both the species. Following attachment to L. camara host roots, intrusive cells of haustoria penetrate the host epidermis and cortex between host cells (Fig. 1, G and H). Similar observations on association between parasite and host plant species have been reported for Orbanche (Lane et al., 1991) and Striga (Losner-Goshen et al., 1998). Anatomical section of S. album haustorium consisted of two regions, one external to the host root, the hyaline body, a structure with high metabolic activity and the penetrating peg, that makes the initial contact with the host roots and penetrate the host tissue. Following the initial haustorial penetration and upon reaching the host root cambium, the penetration peg flattened out laterally to form a thin ellipsoidal disc (Fig. 2). These observations are in conformity to the findings of Tennakoon and Cameron (2006), who investigated the morphology and anatomy of haustoria formed by S. album attached to one of its principal hosts Tithonia diversifolia. The parasitic nature of S. album and formation of haustoria in different host species have been reported by various researchers (Rocha et al., 2017, Lu et al., 2014, Doddabasawa and Chittapur 2021, Rocha et al., 2014). However, most parasitic and physiological studies were conducted on nitrogen fixing and non-nitrogen fixing plant species like Cajanus cajan (Nagaveni and Vijayalakshmi, 2003), economical horticultural crops like Mangifera indica and Phyllanthus emblica (Viswanath et al., 2014) and Citrus aurantium (Singh et al., 2014). Intimate vascular connectivity between S. album and roots of other host species was earlier observed and reported (Rocha et al., 2017, Tennakoon and Cameron, 2006), which revealed the absence of direct lumen-to-lumen xylem connection between xylem of hosts and S. album. This confirms that movement of xylem sap from the host to parasite occurs principally via pits of host xylem elements. Similar findings were observed in S. album haustoria and L. camara roots in our studies (Fig. 1, I). Further, functional status of the haustorial connection between L. camara and S. album by radio-labelling the host (L. camara) are required to confirm this observation.