Results and discussion

(1) Archaeological remains of specific crop species: Domestication of noni took place thousands of years ago, and being a non-food crop, archaeological evidence is difficult to provide and neither has been reported, and hence cannot be used in the present debate. Nevertheless, archaeological sites of Mahagarha and Koldihwa in Indo-Gangetic plains, identified with rice grains of the earliest rice cultivation in the world (Sharma, Reference Sharma1980), and recent archaeobotanical evidence of domestication in parts of South India (Fuller et al., Reference Fuller, Korisettar, Venkatasubbaiah and Jones2004) suggest India to be an important centre of crop origin/early domestication of valuable plant species. However, an archaeological relic of Ganesha from the 1st century CE, discovered in Indonesia from the Ujung Kulon National Park, West Java, reflects ancient connections and influence of Hinduism/India over Indonesia, spread through the distribution of knowledge and material.

(2) Richness in floristic and crop diversity: By virtue of physiognomy and climatic diversity, India harbours a rich flora; consequently, India (subcontinent) has been considered as one of the 12 mega-centres of biodiversity with three hot spots of biodiversity (Conservation International, 2005). However, while organizing the centre of origin according to the richness of cultivated floras, Vavilov (Reference Vavilov1934) put the Hindustani Centre second after the Chinese one. According to a recent generic assessment (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2009), the genus Morinda is represented by two species, M. angustifolia Roxb. and M. persicaefolia Buch.-Ham, in tropical Himalayas, as M. villosa Hook.f. found in the tropical Himalayas is now transferred to Gynochthodes, and by another two species, M. reticulata Gamble (syn. M. coreia Buch.-Ham) and M. citrifolia L. in South Eastern Ghats and Western Ghats, i.e. Andhra Pradesh, Tamil Nadu, Karnataka and Kerala (Gamble, Reference Gamble1921) and Andaman and Nicobar, as M. pubescens J.E. Smith (syn. M. tinctoria Roxb.) is considered an unplaced name in the Kew database (http://apps.kew.org/wcsp/qsearch.do), and M. umbellata L. distributed in the Andaman and Nicobar Islands is transferred to Gynochthodes. Therefore, Southeast Asia and Micronesia and Polynesia are comparatively less rich in floristic diversity and in crop species flora. In fact, these regions are dominated by the species that are an extension of Indo-Burma flora, as reflected by the commonality in the occurrence of a number of taxa both in the north-east region of India and Southeast Asia. It is even true for Morinda; for example, M. angustifolia occurs in continuum from the Himalayan region to Bangladesh, Burma, Thailand, Malaysia, Singapore, etc.

(3) Higher levels of endemism: Because of being bound by the Himalayas in the north and the peninsular region surrounded by the ocean, isolation of Indian flora has resulted in very high levels of endemism. Rubiaceae to which the genus Morinda belongs is one of the families represented by more than 500 species in India, of which 205 (41.0%) are endemic (Nayar, Reference Nayar1996).

(4) Prominent occurrence of the concerned family/genus and wild relatives: Like the family Rubiaceae, according to a revised phylogeny, the genus Morinda is represented by four species in India (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2010), distributed in ecologically diverse regions: M. angustifolia and M. persicaefolia, habitat to the tropical Himalayas, and M. reticulata (syn. M. coreia) and M. citrifolia and its two botanical varieties (citrifolia and bracteata) in the semi-arid Eastern Ghats of Andhra Pradesh and Tamil Nadu and the humid Andaman and Nicobar Islands and in the South Western Ghats of Kerala.

According to the latest assessment, the genus Morinda has 30–35 species with a pantropical distribution (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2009). A comparatively higher number of species in the tropical Pacific islands are probably the result of island biogeography, which has resulted in the differentiation of a number of morphologically distinct orthodox species in various islands. Genetically, they may be the same; however, further investigations using the principles of biological species and molecular markers are required to ascertain the actual number. Hence, in the prominence of occurrence of family, genus and related species, Southeast Asia, Micronesia and Polynesia and South Asia (India) appear to be similar. This is expected, based on the evolutionary geo-history of these regions, according to which India was basically part of the Southern Hemisphere that collided with the land mass of the Northern Hemisphere during the continental drift, resulting in present Indian land mass with floristic components of both the Northern and Southern Hemispheres. Thus, the common occurrence of the genus Morinda in South Asia (coasts of India's mainland and the Andaman and Nicobar Islands), Southeast Asia and the Pacific islands is a geo-historical fact, corroborated by the natural occurrence of M. citrifolia and wild Morinda species in the Asia-Pacific regions, touching the African continent (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2010).

(5) Natural occurrence of concerned domesticated/economically important species: The coastal areas of Tamil Nadu, Andhra Pradesh, Kerala, Karnataka and the Andaman and Nicobar Islands have naturally occurring cultivated noni, which is a small tree type with large to very large ovate to oval light green, green to dark green leaves, white flowers and large fruits with short to very short drooping peduncles. The distribution map presented by Razafimandimbison et al. (Reference Razafimandimbison, McDowell, Halford and Bremer2010) includes these areas along with the Southeast Asia, Micronesia and Pacific regions. It is difficult to say whether they are spread through natural seed dispersal or escaped from local cultivations, or both.

(6) Occurrence of wild or weedy immediate ancestral relatives of the concerned species: In addition to the naturally occurring cultivated, large-fruited type, the coastal areas of Tamil Nadu, Andhra Pradesh, Kerala and the Andaman and Nicobar Islands have another naturally occurring wild weedy shrub to a small tree type of M. citrifolia, with elliptic to lanceolate, thick, leathery, glossy leaves, white flowers and smaller fruits with long, erect peduncles, i.e. M. citrifolia var. citrifolia, which grows under diverse conditions in coastal areas, between rocks, marshy lands, field bunds, roadsides of urban areas, pits of old buildings, etc. Razafimandimbison et al. (Reference Razafimandimbison, McDowell, Halford and Bremer2010) has restricted this variety only to Micronesia, and thus the present observation extends the distribution limits of this variety to India. Probably the similar natural principles of seed distribution are involved in the wide distribution of this variety. Additionally, the Andaman and Nicobar Islands have M. citrifolia var. bracteata, which is very similar to the small-fruited M. citrifolia var. citrifolia, except for the retention of floral bracts even at the fruit/syncarp stage. At the molecular level, M. citrifolia var. potteri, distributed in the Pacific region, has been found closest to the large- and small-fruited M. citrifolia var. citrifolia (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2010). Probably, single gene mutation or chimeras are responsible for its differentiation with leaf variegation. Nevertheless, these three varieties are closely related, based on cluster analysis on morphological traits (Waki et al., Reference Waki, Okpul and Komolong2008) and molecular marker analysis (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2010), establishing the monophyletic ancestry of M. citrifolia.

Two shrub or tree-type species, M. angustifolia, distributed in the eastern Himalayas of northeast India, Assam, Bihar and Andhra Pradesh, and M. reticulata (syn. M. coreia), distributed in the Eastern Ghats of Andhra Pradesh and Tamil Nadu and South Western Ghats, which are morphologically, taxonomically and molecularly part of the Asian clade of Morinda, are next close to M. citrifolia, after the Micronesian species M. pedunculata, M. latibracteata and the Australian species M. bracteata var. celebica (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2010), probably because the Micronesian species are genetically closer to geographically close accessions of the Pacific regions, from which most samples of the large- and small-fruited M. citrifolia var. citrifolia were sampled. These studies need to be extended, with the inclusion of a proportionate number of collections from all areas of geographical distribution, including India, to give a clear picture.

(7) Level of interaction between human and nature: The level of interaction of the human population with natural resources, particularly biodiversity, has been very high in the Indian subcontinent, resulting in the domestication of a large number of species. Vavilov (Reference Vavilov and Love1935) recognized eight primary centres of origin, of which two are associated with India, namely ‘the Indian Centre’ (including the core of the subcontinent) – based originally on rice, millets and legumes, with a total of 117 (168) species – and ‘the Indo-Malayan Centre’ (including the northeast region of India and Southeast Asian countries such as Burma, Thailand, Malaysia, Indonesia, Philippines, etc.) – with root crops (Dioscorea spp., Tacca, etc.) and preponderant fruit crops, sugarcane, spices, etc., of about 55 species. Based on archaeological evidence and the scientifically authenticated Vedic literature, India has been recognized as one of the centres of ancient civilizations in continuity from the Saraswati Valley, Harappan (Indus Valley)/Indus Sarasvata civilization and the Ganga Valley (Vedic, Indo-Gangetic) civilization, and the more recently discovered Cambey region (Chengappa, Reference Chengappa2002), and had played a major role in the domestication of plant species and evolution of agriculture (Lallanji and Srivastava, Reference Lallanji and Srivastava2008). Therefore, it may be reasonable to conclude that noni was discovered and used by ancient Indians first while examining the nature, including plants, not only for food, but also for health and to treat diseases, long before the recorded history of Southeast Asia and the surrounding Micronesian territories. In fact, archaeological and historical evidence from Indonesia, e.g. the discovery of the statue of the Hindu God Ganesha from the 1st century CE, 1500-year-old inscription in Sanskrit of King Purnavarman, and mention of ‘Dvipantara’ or ‘Jawa Dwipa’ by Indian scholars to be in Java and Sumatra in 200 BCE writings, suggests that the Indo-Malayan Centre/Region (Southeast Asia) was dominantly influenced by Indian culture and agriculture with extension of their knowledge and product to the region, a reason for Vavilov to combine this region with India (Indo).

(8) Ecological and socio-political diversity: India offers great diversity both in terms of ecological and socio-political context. Because of being a large landmass with all possible ecological variations from the tropical rainforest of Western Ghats, to the temperate high-altitude regions of the Himalayas, to the Thar Desert of north-western plains, India offers most diverse ecologies for the adaptation of plants. The Gangetic plains, blessed with fertile soil and hospitable climate, have attracted settlers. Because of these attributes, fundamental to agricultural productivity, the Gangetic plains have evolved as a primary centre of plant and animal domestication and agriculture (Tripathi, Reference Tripathi, Lallanji and Srivastava2008). Subsequent activities have led the region to evolve into a seat of one of the oldest civilizations in continuity, including the Vedic civilization (Indo-Gangetic civilization; Indo-Aryan civilization) in northern India, credited to the people referred to as the Aryans (1700–1300 BCE). The myth that the Aryans came from Central Asia is being elucidated by recent scientific and archaeological evidence, and the Vedic literature, concluding that the Aryans were the local people and did not come from anywhere (Swami, Reference Swami and David2008). Similarly, in the recent past, evidence has been growing for early plant domestication in South India, such as minor millets, Vigna spp., fruits, etc. (Fuller et al., Reference Fuller, Korisettar, Venkatasubbaiah and Jones2004), which were indigenous to the Indian peninsula. However, most information about these developments across the Indian continent was documented in the ancient Sanskrit language, the language of the Aryans, the rulers. Therefore, it may be logical to conclude that M. citrifolia being a small tree, native to the South Eastern Ghats and Western Ghats of peninsular India, might have been domesticated in South India, and the information on its potential value was documented in Sanskrit, the language of the ruling Aryans, mother of all the Indian languages, and used all over the country in ancient times. Such probability is corroborated by the discovery of the seeds of jackfruit (Artocarpus integrifolia L.) from Chalcolithic sites at Narhan in the middle Gangetic plains (Saraswat et al., Reference Saraswat, Sharma and Saini1994), along with the seeds of Vigna spp., which are wild to Western Ghats, from where they would have probably been taken to North India for cultivation. A probability supported by the fact that the Sena kings who ruled over Bengal (Vanga) during the 11th to 13th century CE, in the north, originally came from Karnataka, South India (Sengupta, Reference Sengupta2008).

The socio-political and trade expediency of Indian kingdoms led to the expansion of Indian culture (knowledge) during the period of Emperor Ashok to Southeast Asia c. 260 BC, which is evident from the main religion Buddhism being prevalent in the Southeast Asian countries, starting from Burma, Thailand, Malaysia, Indonesia, in south, to China, Vietnam, Mongolia, Japan, etc., in north, and later during the period between 1010 and 1200, by the Chola dynasty, extending their influence up to Malay and the far east, which is evident from the influence of Hinduism in Southeast Asian countries, such as Cambodia (the Temple of Angkor Wat by King Suryavarman II between AD 1131 and 1150) and Indonesia (Prince Aji Saka introduced the writing system to Java based on the scripts of southern India; Hindu kings ruled the area around Kutai on Kalimantan); further to this is the fact that the name Singapore is derived from the Sanskrit word Simha Pura and the name Indonesia from Hind-Asia, translated into Indonesia (Indo-Asia) during the colonial times. Southeast Asia was frequented by traders from eastern India, particularly Magadha (Ashok), as well as from the kingdoms of South India. The trading expeditions during these periods extended up to China via Sumatra, leading to the probable introduction of important crops and medicinal plants, including M. citrifolia (Fig. 1). Similar accounts are not available from Southeast Asia or Polynesia, as observed by Razafimandimbison et al. (Reference Razafimandimbison, McDowell, Halford and Bremer2010): ‘whether or not this form of M. citrifolia var. citrifolia was already present before the arrival of Micronesian and Polynesian ancestors, question on which historical records is silent’.

Fig. 1 Chola Dynasty territories and their trade route c. 1050. A colour version of this figure can be found online at journals.cambridge.org/pgr.

(9) Interest of Royals: The royalties played a major role in the domestication and improvement of plant species (Janick, Reference Janick2007). There is documented information that ancient Indians, called the Aryans, ruled India in c. 1700–1300 BCE (c. 3500 years ago, or even earlier). Their physicians developed the medicine system ‘Ayurveda’ (1500 BCE), from ‘Atharvaveda’ (one of the four most ancient books of Vedic knowledge, wisdom and culture; Bloomfield, Reference Bloomfield1899; Chopra, Reference Chopra and Selin2003). ‘Ayurveda’ has reference of M. citrifolia, being held in very high esteem because of its properties to protect the skin. Compared with this, the documented information on the use of noni by the Polynesians for food and medicinal purposes is 2000 years old (Whistler, Reference Whistler1985).

(10) History of nomenclature/vernacular name used: The oldest references to noni are found only in the ancient Indian language Sanskrit, dating back to tens of centuries, with the name of ‘Och’ plant or ‘Ashyuka’, which means ‘longevity’ (Gerson, Reference Gerson1997). It was noted to be a balancing agent, stabilizing the body in perfect health (Anonymous (Reference Anonymous2009a), toptropicals.com/html/toptropicals/plant_wk/noni.htm; Anonymous (Reference Anonymous2009b), www.immuno-research.com/enoni.htm). In the literature search of Gerson (Reference Gerson1997), more than 100 Indian Sanskrit writings pertaining to noni have been recorded. This reflects that noni was discovered and used by Sanskrit-speaking people, long before the recorded history in Southeast Asia. Noni has names in other South Indian ancient languages from the Eastern Ghats, i.e. Andhra Pradesh and Tamil Nadu. In Tamil, it is called ‘Munja pavattay’, and in Telugu ‘Maddi chettu, Molagha’. The same cannot be said either for Southeast Asian, Micronesian or Polynesian countries, using the noni for food and medicinal purposes since 2000 years (Whistler, Reference Whistler1985). Furthermore, in the international languages, in English, noni is called Indian mulberry and in Spanish, Mora de la India, reflecting the recent global discovery of noni, probably during the quest of the West on a route to the spice-rich East. These facts reveal that Indian knowledge about the potential value of M. citrifolia is older than Southeast Asia, from where the ancestors of Micronesia and Polynesia arrived (Razafimandimbison et al., Reference Razafimandimbison, McDowell, Halford and Bremer2010).

(11) History of domestication of other crops: India is associated with two primary centres of origin, i.e. Hindustani and Indo-Burma, and has domesticated about 168 plant species (Vavilov, Reference Vavilov and Love1935) for food. Additionally, according to the early Vedic literature, a medicinal system called ‘Ayurveda’, meaning ‘the science of life’ in Sanskrit, was developed by ancient Indian settlers (the Aryans in 1500 BCE), using plants for natural treatments. This indicates that these initial settlers, while bio-prospecting plants for food, were also looking for plants for health, generating knowledge about the medicinal properties of plants. ‘Ayurveda’ describes the regular use of about 1500 plant species, including M. citrifolia (Anonymous (Reference Anonymous2007), www.all4naturalhealth.com/ayurvedic-medicinal-plants.html).

(12) History of ancient and diverse use of the concerned species: Most of the facts discussed above reflect that the potential medicinal value of noni was known to Indians 3500 years ago (c. 1700–1300 BCE), long before the Southeast Asians, Micronesians and Polynesians. However, in these regions, noni has been used more traditionally (Davis, Reference Davis, Macpherson, Daniells, Wedding and Davis2007). It has been used as food (during famine), consumed raw or in the form of fruit juice; its leaves, flowers, bark and roots have also been used (red and yellow dye) (Dixon et al., Reference Dixon, McMillan and Etkin1999). In Australia, indigenous people usually eat its fruit raw with salt, whereas in Southeast Asian cultures, it is often cooked in curries. In this regard, India lags behind; probably the richness of floral diversity and domestication of a large number of plants for various purposes facilitated the availability of alternative sources of food and medicine, limiting the use of noni, to a narrow ecological niche of coastal regions, a factor considered to have contributed to non-domestication plant species in the biodiversity-rich region. Nevertheless, there are reports that in Tamil Nadu, noni was cultivated near temples, like Basil (‘tulsi’). Such social domestication cannot be associated with Southeast Asian countries.

Conclusion

Thus, based on the comparative richness of the Indian subcontinent in floristic and crop diversity, higher levels of plant species endemism, prominent occurrence of the family Rubiaceae and the genus Morinda, the natural occurrence of large-fruited, cultivated noni, its wild or weedy immediate ancestors, M. citrifolia var. citrifolia and M. citrifolia var. bracteata, several wild Morinda species, including morphologically and molecularly close, M. angustifolia and M. reticulata (syn. M. coreia) belonging to the Asian clade, home to ecological diversity and that India being one of the primary centres of crop origin (domestication) and diversity with the documented socio-political history of rulers supporting bio-prospecting, domestication of plants both for food and medicine from ancient times (1500 BCE; developing ‘Ayurveda’), and later dispersal (useful plants and products) during the voyage to Southeast Asia and China under the barter trade (still practised with Myanmar), Southeast India appears to be a more probable centre of domestication/origin of noni than Southeast Asia and Micronesia. Furthermore, the oldest reference of noni in the ancient Aryan literature in Sanskrit, describing its medicinal properties, corroborates that it was known to the Indians long before (3500 years) than the Southeast Asians, Micronesians and Polynesians. Morton (Reference Morton1992) also mentioned southern Asia, and Australia as its native land. The occurrence of a greater number of wild Morinda species endemic to various island nations of Southeast Asia, Micronesia and Polynesia can be explained, as a result of island biogeography, isolating populations. However, a comparatively wide distribution of the wild and weedy form of large-fruited M. citrifolia and its two varieties, small-fruited variety, citrifolia and bracteata, across the tropics is due to efficient natural seed dispersal through buoyancy (noni seeds have large air sacs and pits in the cells of the seed's testa, giving them buoyancy), and intentional introduction by migrating humans, who colonized the Indo-Pacific islands (Whistler, Reference Whistler1992). It was further aided by self-pollinating and round-the-year flowering and fruiting capacities. Dispersal might have also been aided by fruit-eating birds and animals.

On the basis of these inferences, it is proposed that M. citrifolia was first domesticated in India in the Eastern or South Western Ghats of peninsular India, documenting the information on its medicinal properties in ancient ‘Ayurveda’ and other Sanskrit writings. At the time of cultural expansion during the period of the Ashoka and/or Chola dynasty or trade voyages from Orissa, Andhra Pradesh or Tamil Nadu, it was carried to Southeast Asian countries (Malaysia, Indonesia), from where the Southeast Asian ancestors of Micronesia and Polynesia brought it to various island nations (Fig. 2). The seafaring Micronesians might have contributed to the further spread of M. citrifolia, through their ocean-going canoes.

Fig. 2 Proposed route regarding the origin and distribution of noni, Morinda citrifolia. A colour version of this figure can be found online at journals.cambridge.org/pgr.

The geological relationship between the Indian subcontinent, Southeast Asia and Micronesia, being part of the same land mass before the continental drift forming the present India, might also suggest the ancient natural distribution of M. citrifolia across these regions and, simultaneously or at different times, polyphyletic domestication. Therefore, Southeast Asia and Micronesia might be the other centre of origin or a secondary centre of origin for noni, as a result of polyphyletic domestication. Nevertheless, detailed phylogenetic investigations are required, including a proportionate number of accessions from all bio-geographical regions of noni and Morinda species, using highly polymorphic molecular markers covering the whole genome, and cluster analysis that will trace the factual phylogenetic relationships among accessions of noni, and between noni and wild Morinda species, identifying the actual bio-geographical region(s) for noni's origin.