REVIEW ARTICLE THE CRADLE OF THE FLOWERING PLANTS Vijai Malik* Department of Botany, CCS University, Meerut Email: [email protected] Received-04.12.2019, Revised-26.12.2019 Abstracts: Angiosperms (Magnoliophyta or Anthophyta), Cycads (Cycadophyta), Conifers (Coniferophyta), Gnetophytes or Gnetales (Gnetophyta) and Ginkgo (Ginkgophyta) are the five major lineages of the extant seed plant. Of these Angiosperms are the most species 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 fossils? he first seed plant appeared near the end of South-east Asia includes the South-eastern part of the T devonian (ca. 370 Mya). The Angiosperms are Asiatic continent (Burma, Thialand, Indo-China and the dominant land plants which have long fossils Malaya) and the Malayan archipelago (Dobby, records going back to earliest cretaceous (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 Jurassic, more than 140Mya. It phytogeographical reasons we include also Assam appears from fossils record (which includes leaves, and tropical Southern China. wood, pollen, flowers & fruit) that angiosperms South-East Asia and the adjoining parts of North underwent a major radiation starting in the early East India, 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 eudicots 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, Magnoliales, Giunea) is a land of living fossils. Laurales, 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 flowering plant 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 basal branch of under environmental stress, probably as a result of the angiosperm tree 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 forest 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 genus 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 flower 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 inflorescence 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 fossil 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 forests. 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