REVIEW ARTICLE

THE CRADLE OF THE FLOWERING

Vijai Malik*

Department of Botany, CCS University, Meerut Email: [email protected]

Received-04.12.2019, Revised-26.12.2019

Abstracts: Angiosperms (Magnoliophyta or Anthophyta), (Cycadophyta), Conifers (Coniferophyta), Gnetophytes or Gnetales (Gnetophyta) and Ginkgo (Ginkgophyta) are the five major lineages of the extant seed . Of these Angiosperms are the most rich and include more than 13000 genera and 300000 species. The Conifers are second largest group of seed plants with ca. 70 genera and 600 species. The cycads include ca. 9 genera and 129 species. Gnetales include only 3 genera (Gnetum, Ephedra and Welwitschia) with 90 species. There is single species of Ginkgo biloba. Caytoniales, Bennettiales, Pentoxylon, Corystosperms and Glossopterids, are the extinct lineages of seed plants. These have been proposed as putative relative and possible progenitors of the Angiosperms (Soltis et al., 2005).

Keywords: Angiosperms, Cradle, Flowering plants, Seed

INTRODUCTION Which part of the globe constitutes South-east Asia and land of living ? he first seed plant appeared near the end of South-east Asia includes the South-eastern part of the T (ca. 370 Mya). The Angiosperms are Asiatic continent (Burma, Thialand, Indo- and the dominant land plants which have long fossils Malaya) and the Malayan archipelago (Dobby, records going back to earliest (ca. 135 1950). In the West, Dobby draws the Northern Mya). Their fossils increase in abundance as we boundary of South-East Asia north of tropic of move through the cretaceous. This group possibly cancer including within it upper Burma; for originated during the , more than 140Mya. It phytogeographical reasons we include also Assam appears from fossils record (which includes , and tropical Southern China. wood, pollen, & ) that angiosperms South-East Asia and the adjoining parts of North underwent a major radiation starting in the early East , East Asia and Melanesia (i.e. region cretaceous (Friis et al., 2011). Fossilized pollen which include four independent countries of documents the presence of the at the early Vanuatu, the Solomon Islands, Fiji, and Papua New cretaceous. Major Angiosperm lineages can be Guinea as well as French special collectively of New recognized in fossils remains by the mid-cretaceous Caledonia and the Indonesian region of Western New (e.g. water lilies, Chloranthaceae, , Giunea) is a land of living fossils. , Monocots and Eudicots were presents). What is the cradle of the flowering plants? The oldest unequivocal fossils are pollen grain from According to Takhtajan (1969) Cradle of Flowering about 140 Mya. The placement of water lilies near Plants is a region in which flowering plants the base of Angiosperms and their early appearance experienced a long period of evolution during which in the fossils records (Friis et al., 2011) should be the principal families and many genera were taken to mean that the first were differentiated. This region may be their centre of aquatic; instead many of their characteristics can be origin probably not very far from their birth place. interpreted as specialization that evolve within this Takhtajan was of the opinion that angiosperms arose one lineage. Indeed, the likely most branch of under environmental stress, probably as a result of the angiosperm leads to the single living adaptation to moderate seasonal drought on rocky species Amborella trichopoda known as first fruit mountain slopes, in an area with monsoon climate. plant. This shrub, endemic to the understory of The regions in which climatic factors have greatly the tropical island of New Caledonia, is thus the promoted the diversification of modern flora are the probable sister of all ~300 000 other living Cape region of South Africa, the Ethiopian angiosperms. Recent evidence has shown that highlands, parts of the Indian Peninsula, South- Archaefructus is one of the earliest and extinct central Mexico, Northern Venezuela, the coast of aquatic of flowering plants discovered from Equador and the Northern provinces of Argentina. China. Archaefructus includes three described Takhtajan (1969) in his book "Flowering plants, species viz. Archaefructus liaoningensis (Sun et al., origin and dispersal" described the Cradle of the 1998), Archaefructus sinensis (Sun et al., 2002), and Flowering Plants under following headings- Archaefructus eoflora (Ji et al., 2004). Sun et al., 1. The tropical origin of flowering plants (2002) called Archaefructus as first due to its 2. Cradle of the flowering plants may be between early age although its position and relationship is a Assam and Fiji matter of controversy. 3. Centre of origin or Centre of Survival

*Corresponding Author ______Journal of Plant Development Sciences Vol. 11(12) : 689-696. 2019 690 VIJAI MALIK

1. The Tropical origin of Flowering plants cretaceous. Thus, Takhtajan was of the opinion that Some authors consider Cradle of Flowering Plants in Arctic or Antarctic origin of Angiosperms must be high latitude and favor an Arctic or Antarctic origin rejected. whereas other favors Cradle of Flowering Plants in During the past century an accepted view was that the lower latitude of tropics or subtropics. The most the flowering plants had originated in all regions of widely supported hypothesis suggested by Heer North Hemisphere, from Arctic to Tropic. Seward (1868) is Northern polar origin of Angiosperms. (1926, 1933) considered this on the basis of fossils According to this hypothesis the Angiosperms discovered of leaves and of Artocarpus originated in the polar region of the Holarctic from Lower Cretaceous in Greenland in Arctic. He (The Holarctic is the name for the biogeographic believed that during that period the climate of this realm. It encompasses all the nontropical parts of region was warm. On the other hand Krassilov Europe and Asia, Africa north of the Sahara, and (1982) and Vakhrameev (1978 and 1991) suggested North America south to the Mexican desert region. that Atlantic coasts, central Asia and Mongolia are This vast region is often subdivided into the the fountain head of flowering plants. But many Palaearctic (Old World) and Nearctic (New World) scientists are of the opinion that the flowering plants subregions) and from here these spread in successive originated in tropical regions and spread towards waves across the whole earth. This hypothesis was polar areas during course of rapid diversification. strongly supported by Saporta (1877), Hooker According to this view the area which has largest (1879), Asa Gray, Adolf Engler, Berry, Chaney, and number of primitive extant angiosperms can be many other palaeobotanist and phytogeographers. possible cradle home and also center of diversity, Similar view on evolution and expansion of various where there are large number of species that will be animal groups have been expressed by the center of origin. Zoogeographer e.g. Mathew in book "Climate and Stebbin (1974) suggested that tropical rain forest is Evolution" (1915, 1939) maintained that the North the asylum into which freshly produced flowering temperate zone was the chief centre of evolution of plants somehow migrated and have since been terrestrial vertebrates. preserved in more or less unchanged. Evidence Another view regarding cradle home of flowering Polar or generally northern origin of Angiosperms is plants is from Schuster (1972), Axelarod (1959, supported by presence of many genera common to 1970) and Brenner (1996) who believed it is both flora of Eastern Asia and Atlantic states of Gondwanaland. North America. According to Axelarod (1959, 1970) the tropical Criticism upland of Gondawanaland with seasonal draught in It is now quite clear that climatic conditions in the the early Mesozoic world would have been the best Arctic has always been unfavourable for the place of flowering plants. development of any rich and varied vegetation. Schuster (1972) considered that because of the According to Edward (1955) the Arctic and Antarctic presence of luxuriant primitive flora in south east with their long winters of comparative darkness are Australia, allowing Lausarian derived flora most unlikely places for the development of new intermingled with Gondwana flora the cradle of groups. Croizat (1952) also strongly criticized the home is Gondwanaland. idea of Northern origin of Angiosperms. The North Since polar hypothesis for the origin of angiosperms Polar Region is particularly poor in records of does not explain adequately the present distribution the cretaceous and tertiary floras. Evidence also of plants, so many workers turned to seek the cradle indicates that there have never been a tropical warm of their nativity in the lower latitudes- the tropical climate in the Polar Regions and the atmospheric and subtropical regions. In this way many authors conditions of extremely low temperature and like Hallier, Diels, Bailey, Axelrod, Thorne etc. came prolonged darkness certainly do not favor out in the favor of tropical origin of Angiosperms. development of tropical . Aquatic origin of Angiosperms The fossil evidence suggests that angiosperms did After the discovery of Archaefructus and Hyrcantha not establish in the Arctic until the late Cretaceous, from northeastern China Sun et al., (2002) and since angiosperm fossils from the early Cretaceous Dilcher et al., (2007) suggested the possibility of (144 million year) are found only at low latitudes i.e. aquatic origin of angiosperms because Archaefructus 450 N and 450 S (Takhtajan, 1969). On the other looks like some aquatic extant angiosperms e.g. hand, the Arctic may have been an important site for Alismataceae, Cabombaceae and Nymphaeales. some level of floral evolution in the late Cretaceous Terada et al., (2005) has suggested that i.e. 95.5-65 million year ago. In both Northern and Archaefructus may have two aquatic habitats, one in Southern hemisphere, Angiosperms reached the medium shallow water such as that of A. sinensis, as higher latitude only at the end of the early cretaceous its larger size suggests, and the other probably very (144 million year, in the Albian), and in these near the lake bank in very shallow water as the latitudes they did not replace the relict Jurassic type smaller size of A. liaoningensis might suggest. of vegetation until the beginning of the late JOURNAL OF PLANT DEVELOPMENT SCIENCES VOL. 11(12) 691

2. Cradle of Flowering Plants may be between be reached. Thus it is valuable evidence in support of Assam and Fiji the hypothesis that cradle of Angiosperms was According to Hallier (1912) the birth place of situated somewhere between Assam and Fiji, most Angiosperms is in the basin of Pacific Ocean on the probably in the area corresponding to what is now hypothetical continent of Pacifica. He considered that South-east Asia. From South-east Asia, Angiosperms ancestors of Angiosperms might probably be found spread over the entire Northern hemisphere. in places like Andes (from Maxico to Patagonia), the Temperate and subtropical elements were able to Hawaiian Island, New Caledonia and New Zealand. reach North America very early by way of North But recent geological investigations do not support it. Pacific track across the Bering-Aleutian area. From According to Bailey (1949) the present floras of South-East Asia Angiosperms could well have Northern Australia, New Guinea, New Caledonia, colonized also the territories of Southern hemisphere. Fiji and the adjacent areas northward to Southern A serious flaw in the South-east Asian center of China provides the largest number of missing links in origin theory, acknowledged by Takhtajan (1969) the chain of Angiosperm phylogeny. According to himself, is the lack of fossil evidence. Hughes (1994) Axelrod (1959) Angiosperms also appeared to have has argued directly for the primacy of the fossil invaded Northeast Asia gradually from the south record to reveal events of the past. during the early Cretaceous i.e. 144 mya. Golenkin Komarov (1908) gave a general conclusion which is (1927) suggested the southern part of the Angara true for phylogenetic series of higher taxa like continent (with Oceania) as the possible place of genera, families and orders. It states that the origin of the angiosperms, but unfortunately gave no geographical distributions of plants must be based reasons for the suggestion. primarily on the distributions of series, not on those This is very striking that many primitive families of isolated species, because these there are a much which are restricted geographically are found on the greater element of uncertainty and chance for islands and borders of the Pacific Ocean. Such species. Study of such series can give not only a primitive families concentrated about the pacific picture of their evolution in time, but also the basin are , Degeneriaceae, direction of their movement in space. Thus, when Himantandracae, Eupomatiaceae, Winteraceae, analyses of a sufficiently large number of Austrobaileyacae, Amborellaceae, Gomortegaceae, phylogenetic series all produce similar results then, Lactoridaceae, Calycanthaceae, , our conclusions for the centre of origin and centre of Tetracentraceae, , etc. But in dispersal true. The more closely they agree, the more number of primitive forms the Eastern part of the certain the correctness of our conclusions. We should pacific basin is clearly inferior to the western part not conclude the birth place of angiosperms on the which includes a wide area from Assam, China and basis of existing geographical distributions of taxa Japan to Australia, New Zealand, New Caledonia and which consist of only distinct isolated the Isles of Fiji (Takhtajan, 1969). representatives. Besides, we should conclude the According to Takhtajan (1969) Cradle of Flowering birth place of angiosperms if distinct taxa form well Plants must be sought in Eastern and South-eastern marked phylogenetic series. Asia, Australia and Melanesia. Geographical Thus, Takhtajan (1969) has stated that it is distribution of primitive Angiosperms like impossible to ignore the fact that the primitive Magnoliales shows that it was this part of the world members of many groups of angiosperms, especially which had been (if not the birth place) the original of the more primitive groups, themselves clearly tend center of widespread cretaceous expansion of to occur in south-east Asia and the neighboring flowering plants. regions of the western Pacific Ocean basin. In the Most probably „cradle of the angiosperms‟ was area between Assam and Fiji grow not just isolated situated in South-East Asia (including Burma, primitive types, but whole groups of closely Thailand, Indo-China, and Malaysia) where greater interrelated genera and even families. concentration of primitive Angiosperms families Distribution of some primitive families (e.g. Magnoliaceae and Winteraceae fig. 1 & 2) are (Takhtajan, 1969): found (Takhtajan (1969). Thus this area or area near The species of Magnoliaceae are concentrated in to it was the cradle of Angiosperms. Takhtajan greater number in east and South East Asia. In (1969) has suggested that the „cradle of the America its species are very poor, whereas in Africa angiosperms‟ occurs somewhere between Assam and they are completely absent. All the 12 genera of this Fiji. But it cannot be said with exactly where family are found in East and South East Asia and between Assam and Fiji the area was in which the most primitive genera and species are confined to Angiosperms first developed. that region. Of the 12 genera of the family only three Croizat (1952) emphasized the importance of are found in America viz. Magnolia, Talauma, and Malesia as a centre of phytogeographical Liriodendron. Certainly the Magnoliaceae came to connections. According to him Malesia is one of the America from Asia probably by two routes, a most important phytogeographic zones of the world northern and a southern. The northern route was and from its boundaries all five continents can easily taken by Magnolia and Liriodendron. The southern 692 VIJAI MALIK route was taken by Talauma. The most primitive Thialand and Indo-China to Java with most primitive species of Magnolia and Talauma are found in Asia species of this genus in continental part of South- including all the main stages of evolutionary East Asia (Fig-1). development of Magnolia with species like M. The family Winteraceae are rival in its primitiveness griffthii and M. pterocarpa and M stellata. The with Magnoliaceae. The largest and most primitive section Maingola of genus Magnolia is most genus Drimys of this family is found in Philippines, primitive and is found in Assam and Upper Burma Borneo, Celebes, Amboina, New Guinea, Eastern and through Indo-China to the Malayan archipelago Australia, Tasmania, Juan Fernandez, and America with species like M. griffthii (Assam and Upper from Mexico to Cape Horn. Next primitive genus of Burma), M. paeliana and M. guatavii (Assam), M. this family is Bubbia whose species are mostly found annamensis (Annam), M. maingayi (Malayan in old world i.e. New Guinea, Queensland, Lord peninsula and Sarawak), M. aequinoctialis (Sumatra) Howe Island, New Caledonia, and Madagascar (Fig- and M. macklotii (Sumatra and Java). Manglietia, a 2.). South Eastern genus is very close to Magnolia and The Degenariaceae are endemic to Fiji and also in some respects it is more primitive than Himantandraceae occur in North East Australia, New Magnolia. Manglietia is found from the Eastern Guinea, and the Mollucas. Himalayas, Assam and South China through

Fig-1. Distribution of Magnoliaceae in world

Fig-2. Distribution of Winteraceae in world JOURNAL OF PLANT DEVELOPMENT SCIENCES VOL. 11(12) 693

Fig-3. Distribution of Amborellaceae in world

North-east India as cradle of Flowering plants 2. This region is regarded as the place of origin The flora of India represents taxa of different of progenitors of many cultivated crops. countries like Afghanistan, Bhutan, Bangladesh, 3. North-east India is richest in biological China, Nepal, Pakistan, Myanmar, Malaysia, diversity at community level, at the species level, and Indonesia, Thailand and some European countries in endemics. like Africa, America, and Australia etc. Himalayan 4. North-east India is recognized as refugium region of India is supposed to be much younger than of flowering plants with higher evolutionary Deccan Peninsula and North East India, as it harbors activities and active center of speciation. most of the advanced families. Assam, North East India is considered as a sanctuary of primitive India, Deccan Peninsula etc are the older flowering plants. North-eastern region of India phytogeographical regions of India and the age of (Assam & Arunachal Pradesh) contain more than 130 these regions is more or less identical in age with Sri primitive Angiosperms like Altingia excelsa, Lanka, South West China and Malaya Peninsula. Aspidocarya uvifera, Betula alnoides, Decaisnea North-East India shows its floristic relationship with insignis, Euptelea pleiosperma, Exbucklandia Myanmar, South West China and Malaya Peninsula. populnea, Haematocarpus validus, Holboellia It has the richest reservoir of plant diversity in India latifolia var. angustifolia, Houttuynia cordata, and forms part of one of the „biodiversity hotspots‟ Magnolia caveana, M. grifflthii, M. hodgsonii, M. of the world. Takhtajan (1969) has suggested North pterocarpa, Pycnarrhena pleniflora, Tetracentron Eastern region of India as the true “cradle of sinense and species of Camellia, Magnolia, Michelia, flowering plants” because Rhododedron, orchids and several wild and 1. Primitive plant families such as economic plants. This suggests that perhaps in this Magnoliaceae, , , region evolutionary development of Angiosperms Degeneriaceae, Tetracentraceae and Lardizabalaceae have taken place. Primitive 9 families with their are well represented here. genera in India (Rao, 1997) are given in the following table-1.

Table 1. Name of Family Name of Genera Magnoliaceae Magnolia, Manglictia, Michelia, Pachylarnax, Paramichelia, Talauma, Tetracentraceae Tetracentron Illiciaceae Illicium Eupteliaceae Euptelea Alphonsea, Annona, Artabortys, Cyathocalyx, Desmos, Fissitigma, Friesodielsia, Goniothalamus, Melodorum, Miliusua, Mitrephora, Orophea, Polyalthia, Trivalvaria, Unona, Uvaria Myristicaceae Horsfieldia, Knema, Myristica Schizandraceae Kadsura heteroclita Lauraceae Actinodaphne, Alseodaphne, Beilschmiedia, , Cryptocarya, Dehaasia, Endiandra, Lindera, Litsea, Machilus. Neocinnamomum, Persea, 694 VIJAI MALIK

Phoebe Chloranthaceae Chloranthus elatior

According to Hutchinson (1969) Magnolia with the earliest diversification of ancient pterocarpa of North-East India is perhaps the most angiosperms was western Liaoning in East Asia. On ancient species of living Angiosperms. But according this basis Sun (1998) and Sun et al. (2002) proposed to recent view Amborella trichopoda is the first fruit the hypothesis of “Eastern Asian Origin of plant. Angiosperms”. According to this hypothesis the Recent View ancient angiosperms might first occur at the middle Eastern Asian origin of Angiosperms latitudes of East Asia, covering the territory of Archaefructus is one of the earliest and extinct western Liaoning, Mid-Eastern Monglolia, Russian aquatic genus of flowering plants. It was discovered Baikalia and Far-East (Fig-4). This region probably from China in the past decade. It had very primitive contained some difficult paleoenvironmental floristic characters of ancient angiosperms. It was challenges under which plants might live, such as found in western Liaoning and its neighboring areas volcanic activity, arid or semiarid climates, often in the East Asia at northern middle latitudes. Thus, isolating plant populations during pre-Cretaceous logically the place of origin (or one of the places) time (Sun et al., 1998, 2002).

Fig-4: Sketch of a suggested center of origin of angiosperms in the world (redrawn from Sun et al., 2001, 2002)

Centre of Origin or Centre of Survival of their origin, but they may be persisted and found Takhtajan considers south-east Asia (including far away from the area of their origin. Amborellales Burma, Thailand, Indo-China, and Malaysia) to be are now only found New Caledonia, which emerged the most likely region where angiosperms originated, from ocean ca. 37 million years ago. Amborella must since this is the region where the highest abundance have lived elsewhere for a long time before it of primitive angiosperms occurs at present. dispersed to New Caledonia and became extinct in its Descendants of the first angiosperms may have original area of occurrence (Christenhusz, et al., dispersed far from their point of origin (Takhtajan, 2017). Thus, on the basis of present distribution of 1987). So current distribution of Angiosperms may living angiosperms it can be concluded that the not necessarily be similar to those of the past. In a islands and peninsulas of South-East Asia is mere a phylogenetic series, “the most advanced members are refugium or centre of survival, of primitive farther from the centre of origin” (Takhtajan, 1987). angiosperms and it is not the cradle and initial Thus, it is not necessary that all primitive distribution centre of angiosperms. Angiosperms concentrated in South-East Asia. They Why America, Africa and Madagascar are not are also found outside South-east Asia. Primitive cradle for flowering plants? forms are not only found within the area of their According to Takhtajan (1969) the extensive region origin of taxa but they are also found outside it. Taxa between Assam and Fiji cannot be simply a may have been completely disappeared from the area 'refugium' of ancient Angiosperms, or in other words, JOURNAL OF PLANT DEVELOPMENT SCIENCES VOL. 11(12) 695 merely a centre of their survival. In fact during the the Angiosperm of tertiary period are too Mesozoic and Cainozoic climatic and general fragmentary that it cannot serve as material for physiographical conditions were no more stable in phylogenetic and phytogeographical analysis in the the area of east and South-east Asia, Australasia, and same way as living Angiosperms living today. Melanesia, than in tropical America or even in Epilogue tropical Africa. Darwin in his famous letter to Joseph Hooker in July Inspite of that, the extremely rich flora of tropical of 1879 described the Cretaceous diversification and America is significantly poorer in primitive subsequent rapid rise of flowering plants angiosperms than the flora of the western part of the (angiosperms) as an “abominable mystery”: how Pacific basin, and the flora of tropical Africa is could they have achieved worldwide ecological almost devoid of them. dominance by early Paleogene times when the oldest It is difficult explain why no members of the angiosperm fossils are only Cretaceous in age?. The Magnoliaceae, Winteraceae, Himantandraceae, father of evolutionary theory could not fathom this Dageneriaceae or any other archaic family have rapid diversification and rather invoked the idea that survived in the African flora, if they had existed 'there was during long ages a small isolated continent there previously. Of the family of the Magnoliales, in the Southern hemisphere, which served as the only the Canellaceae and the Annonaceae are birthplace of the higher plants'. However, recent represented in Africa. In Madagascar besides phylogenetic and palaeobiogeographical analyses Canellaceae and Annonaceae, Winteraceae (Bubbia have suggested origin for the stem perrieri), and Chloranthaceae (Ascarinopsis coursii) angiosperms. Takhtajan (1969) concluded that the as well the endemic family Didymelaceae are also original center of distribution was situated found. somewhere between Eastern India and Polynesia. In Although primitive Angiosperms are appreciably all probability it was the part of the world that is numerous in America than in Africa and today South-East Asia. Probably this conclusion is Madagascar, even in America they are still far fewer right but it cannot claim to be certain. After the and, as a rule, more specialized than in East and discovery of Archaefructus Sui Ge et al. (1998) South-East Asia. The American Members of suggested that the Eastern Chin dawning site or one Magnoliaceae and Winteraceae (appear to be more of the regions of the origin site of flowering plants. advanced than those in South-East Asia), for She remarked that, progress in the study of dawning examples, are markedly inferior in number and process of flower has always been insight and the diversity to those of the Western Pacific (South-East discovery of Archaefructus is only the first step in Asia) and are representative of the less primitive demystifying the 'abominable mystery' put by forms (Takhtajan, 1969). So America, Africa and Darwin (1859) on the early evolution of flowering Madagascar are not possible sites for the “cradle of plants. the angiosperms”. Several primitive Magnoliales and other living REFERENCES fossils grow in Assam, Upper Burma, , Mountain region of Thialand, Loas, and , Axelarod, D.L. (1961). How old are the Malesia and Melanesia. 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