Preserved gum in an Early Cretaceous Welwitschiacean.

A wide variety of vascular plants produce fluid exudates such as resins and gums, with each group differing in chemical definitions. Due to similarity in physical appearance distinguishing exudates based on chemistry is vital, for example gums and resins are visually similar resulting in these terms being used interchangeably. However, their chemical definitions are very different; resins are composed of lipid-soluble terpenoids, while gums are complex, highly branched (non-starch) water-soluble polysaccharides. A common example of this misunderstanding is the Eucalyptus, which is known as a Gum Tree, but nuclear magnetic resonance analysis of the Eucalyptus exudate shows its composition to be polyphenolic and is therefore actually a kino (i.e. neither a gum nor a resin, bt closer in composition to resins). Differences between gum and resin can also be seen in the functional roles within the plant. The main roles of resins are to respond to wounding, as a defence against pathogens and to dissuade herbivory by Insects and other organisms. Gum is involved in food storage, structural support, and also for wound sealing, but there is no common role across taxa. Further confusion arises as some plants, e.g. Boswellia and Commiphora species, even produce exudates with a mixture of polysaccharide and resin components (the gum resins Myrrh and Frankincense respectively). Until now only fossilised plant resin (ambers) and latex filaments have been reported preserved in the fossil record. While the fossilisation of fluid exudates might seem unlikely, the fossilisation of resin is relatively common, and extends back some 320 million years to the Carboniferous, but chemically confirmed gums have never been reported.

In a paper published in the journal Scientific Reports on 25 February 2020, Emily Roberts of the School of the Environment, Geography and Geosciences at the University of Portsmouth, and the Department of Palaeontology at the University of Vienna, Leyla Seyfullah, also of the Department of Palaeontology at the University of Vienna, Robert Loveridge, also of the School of the Environment, Geography and Geosciences at the University of Portsmouth, Paul Garside of Conservation Research, at the British Library, and David Martill, again of the School of the Environment, Geography and Geosciences at the University of Portsmouth, describe the first known incidence of preserved gum in the fossil record, in a preserved Welwitschiacean leaf from the Early Cretaceous Crato Formation of Brazil.

The Early Cretaceous (approximately 120 million year old) Crato Formation utcrops on the northern flanks of the Chapada do Araripe, a plateaux on the border between Ceará, Pernambuco and Piauí States in northern Brazil. In is noted for the exceptionally well preserved fossils from the Nova Olinda Member, which include Dinosaurs, Crocodiles, Fish, Pterosaurs, Crustaceans, Arachnids, Plants and most notably Insects, which are present in large numbers, often showing exceptional preservation hese Insects are of particular interest as they date from a time in the Early Cretaceous when Flowering Plants were rapidly diversifying, and relationships between Insect and Plant groups that would come to dominate the Earth’s terrestrial biology were being formed.. Investigations of different groups of fossilized Animals from the Crato Formation show that they are preserved as various mineral replacements, and their preservation was microbially-mediated.

Stratigraphy of the Crato Formation. Stratigraphy of the Araripe Basin indicating the fossil bearing laminated limestones of the Nova Olinda Member of the Crato Formation. Roberts et al. (2020).

Amber has also previously been reported from the Crato Formation Lagerstätte, inside fossil plant remains and as isolated clasts, and is attributed to Conifers. The fossil leaves occur as compressions showing at least some three-dimensionality. An amber-coloured substance is visible in some of the fossil leaves of Welwitschiophyllum brasiliense from the Crato Formation.

Fossil Welwitschiophyllum leaves from the Crato Formation, Brazil showing three- dimensional preservation. (a) Complete Welwitschiophyllum leaf (UOP-PAL-MC0002). Showing three dimensionality. (b) A magnified view of Welwitschiophyllum (UERJ 14-P1) showing that the leaf is preserved three dimensionally with distinct parallel leaf tissues. Scale bars, (a) 10 mm (b) 5 mm. Roberts et al. (2020).

Welwitschiophyllum is considered a relative of the extant Gymnosperm Welwitschia mirabilis, the sole member of this Gnetalean genus. The Welwitschiaceae have a sparse macrofossil record, fossils assigned to this family, including Welwitschiophyllum, derive solely from the Crato Formation. However, the pollen record shows Welwitschiaceae were once a diverse and prevalent group that saw a decline with increasing Angiosperm pollen. Today, Welwitschia is restricted to the Namib Desert in Namibia and Southern Angola and has chemically confirmed gum in both the cone and in abaxial ducts within leaves.

Roberts et al. investigated this amber-coloured substance inside fossil Welwitschiophyllum leaves to test whether Welwitschiophyllum produced a resin (now fossilised as amber), or a gum like its presumed extant relative Welwitschia, using Fourier-transform infrared spectroscopy and Attenuated total reflectance spectroscopy. They report the first geochemical evidence for fossilised gum preserved inside Welwitschiophyllum leaves, and suggest areas for future investigation to understand how a roughly 120 million year old gum may have survived.

Fossils of Welwitschiophyllum occur as long detached leaves up to 850 mm in length with thin bands of an amber-like substance. These are particularly visible where the fossil surface has been abraded or removed. This substance in the Welwitschiophyllum leaves resembles amber in ducts, lying parallel to the long axis of the leaves. These ducts are inferred here as adaxial (upper leaf surface) due to the curvature of the leaf base. However, the absence of preserved cuticle and other anatomical features, means that their precise orientation cannot be confirmed. This constituent arrangement contrasts with the traumatic formation of gum in its presumed relative Welwitschia. Slight compaction of the specimens gives these ducts an ellipsoidal cross section, but they appear to have a repeating pattern showing a principal duct followed by a secondary duct ranging in diameter from 75 μm to 200 μm.

Fossil Welwitschiophyllum leaves with gum ducts from the Crato Formation, Brazil. (a) Complete elongate fossil leaf (UERJ 13-P1) showing a curved base and degraded fibrous apex, with a partially abraded surface (lighter part of fossil) exposing the internal leaf tissue and linear gum duct arrangement. (b) Detail from (a) (UERJ 13-P1) where the gum ducts appear as amber-brown structures within Welwitschiophyllum leaf tissue. (c) Transverse thin section through the fossil leaf (UERJ 14-P1) with arrowheads indicating the orange coloured gum ducts within the brown leaf tissue. The black line of tissue may be compressed remains of vascular tissue (below the leaf is the preserving sediment). (d) An oblique thin section of the leaf (UERJ 14-P1) showing the repeating pattern of the amber-coloured gum ducts. Scale bars, (a) 20 mm (b) 3 mm, (c) and (d) 500 μm. Roberts et al. (2020).

Analysis using Fourier-transform infrared spectroscopy and Attenuated total reflectance spectroscopy are commonly used on both living and fossil plants showing that complex biomolecules survive and are identifiable in the fossil record Fourier-transform infrared spectroscopy analyses compare living and fossil resin and gum samples. Additionally, Attenuated total reflectance spectroscopy analysis confirms that the amber-coloured substance in the fossil leaves, which was extracted and purified for testing, generated a spectrum closely matching those of published gum signatures and is remarkably similar to that of Welwitschia gum.

Thin section of a Welwitschiophyllum leaf. Thin section through the fossil leaf (UERJ 13-P1) showing amber-coloured gum ducts within brown leaf tissue. Scale bar, 500 μm. Roberts et al. (2020).

The discovery of in situ preserved plant gum is unusual because of its solubility in water. This is particularly striking in a formation thought to be deposited in a hypersaline lagoon setting. Solubility experiments were undertaken on Welwitschia gum to determine whether the increased salinity of the lagoon may have affected the solubility of the gum in any way. In the freshwater, brackish, normal marine, and hypersaline water tests the extracted gum dissolved within 49–59 minutes, showing that salinity does not affect solubility, and therefore the preservation (or not) of exposed gum.

Roberts et al.'s analyses of the amber-coloured substance inside the fossil Welwitschiophyllum leaves shows a distinct chemical spectrum that clearly differs from those of ambers and resins, but which closely compares to plant gum spectra. This means that the recovered substance from the Crato Formation fossil Welwitschiophyllum leaves is a preserved gum and not an amber formed from resin. The chemically detected presence of gum in ducts inside two separate fossil leaves confirms that this is not an isolated occurrence within these Crato Formation fossils.

Due to the soluble nature of gum, its preservation in the fossil record is unexpected. This is particularly notable here as the leaves containing gum were firstly deposited in a hypersaline lagoon, then later this deposit was exposed to continental weathering. Thus, water featured in both the formation and weathering of the Crato Formation, yet the gum persisted. The gum solubility experiments showed that in each case of differing salinities the extracted Welwitschia gum dissolved, so saline levels appear to have no bearing on gum preservation.

How the gum came to be preserved is currently not understood and further investigation is needed into the taphonomic and diagenetic processes surrounding these gum-preserving fossil leaves. We can speculate that there are at least two factors involved. Firstly, the nature of the microbially-mediated taphonomy and diagenesis in the Crato palaeo-lake setting has been shown to be critical in the preservation of labile structures in animals from the Crato Formation Konservat-Lagerstätte. Secondly, perhaps only in part, the coriaceous nature of the fossil leaves played a role. Both the surrounding duct tissue and the large amount of resistant embedding leaf tissues would have provided some protection from dissolution in water. In extant Welwitschia the outer walls of the epidermal cells are specialised with three layers, thickening and strengthening the epidermis, but the preservation of the fossil leaves prohibits epidermal comparison. The regular arrangement of ducts in Welwitschiophyllum suggests that they were formed through duct initiation, i.e. constituent, as opposed to the stress initiated response known as gummosis. Their formation was likely to be used for food storage or structural support, signifying that the hydrophilic gum was constituent within the fossil leaves.

Despite the very low preservation potential of a highly water-soluble exudate, the first preserved gum was recovered from the Early Cretaceous. This fossil gum presents a chemical signature remarkably similar to gum in extant Welwitschia and distinct from those of fossil resins. This shows that gum production in plants extends back into the fossil record by at least 120 million years. This is then the first report of a highly soluble biomolecule recovered from the Crato Formation and future work should focus on how this preserved gum survived. Furthermore, fossilised plants with observed internal ‘resins’ should be chemically confirmed in case further instances of gums or other types of plant exudate can be identified from the fossil record.

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Cycas revoluta: Cycads 'flowering' on the Isle of White.

The Ventnor Botanic Garden on the Isle of Wight, southern England, has reported that a species of Cycad, the Japanese Sago Palm, Cycas revoluta, (not actually a Palm) has begun 'flowering' on the island, for the first time in Human history. The 'flower' of a Cycad is not a true flower, it is a modified cone, similar to that of a Pine or other Gymnosperm, but is modified for Insect pollination (typically by Beetles), making it large and conspicuous. Cycads are dioeceous, which is to say each plant is either male or female, and typically produce only one large 'flower' each breeding season. They were a dominant Plant group during the Mesozoic, but today are restricted to warmer climates, with the most northerly populations known in Florida and southern Japan. The youngest fossil Cycads from Europe come from the Oligocene Frauenweiler clay pits of Baden-Württemberg in Germany, deposits dated to between 33.9 and 28.4 million years old. They are widely grown in Europe as introduced ornamentals today, but this appears to be the first instance of them flowering outdoors in Northern Europe recorded. The event has been linked to the exceptional heatwave being experienced in Europe at the moment, with many areas having recorded their hottest ever temperatures this summer. Both male and female plants have been flowering at the Ventnor Gardens, and as the area is not home to pollinating Cycad Beetles, and the plants are too far apart to cross-pollinate by other means, staff at the gardens intend to pollinate them artificially.

A male Cycad flower on the Isle of Wight this year. Ventnor Botanic Garden.

Cycad’s are of particular interest to botanists and horticulturalists due to their unique evolutionary heritage; they are Gymnosperms (non-flowering Seed Plants), members of the group that includes Conifers and Ginkos, but among the closest non-flowering relatives of the Angiosperms (Flowering Plants). They large attractive plants, superficially resembling Palms, but producing large and often brightly coloured strobili, structures intermediate between cones and flowers; these are often pollinated by Beetles or Thrips.  Cycads are thought to have originated during the Permian, and became dominant Plants in many ecosystems during the Jurassic and Cretaceous, but suffered heavily during the End Cretaceous Extinction, and there are about 330 species surviving today, predominantly in the Southern Hemisphere, most of which diversity is thought to have arisen from a post-Cretaceous radiation.

 The approximate distribution of Cycads today. Wikimedia Commons.

There are over 330 known living species of Cycads, the majority of which are listed on the International Union for the Conservation of Nature’s Red List of Threatened Species, with more than 75% of known species currently thought to be threatened with extinction. Cycads are threatened by habitat loss and invasive species (particularly Insects), but are considered to be most at risk due to over-collecting for horticulture. The distinctive evolutionary history of the plants, combined with their attractive appearance and drought tolerance, makes them highly sought after by plant collectors, however they are slow growing and difficult to raise from seed, resulting in a high market value for mature plants, which leads to many being taken from the wild. Four species of Cycad are considered to be extinct in the wild, and it is not thought it will be possible to reintroduce them to their former environments, as Cycads are usually co-dependent on single species of pollinators, typically Weevils, with neither species able to survive in the absence of the other.

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Tobleria bicuspis: The earliest cone-producing Conifer?

Modern Conifers bear their seeds in cones, structure in which the seeds are attached to scales arranged spirally on a central bract. A similar situation is seen in Conifers from Mesozoic and Cainozoic deposits, but the earliest, Carboniferous Conifers, placed in a group called the Voltziales, are somewhat different, with seeds found in the axils of fertile leaf shoots (the angle between the base of the leaf shoot and the stem), which are arranged in a loosely radial pattern on a stem. The first seed cones appear in the Voltziales towards the end of the Early Permian.

In a paper published in the journal PhytoKeys on 25 March 2019, Isabel Van Waveren of the Naturalis Biodiversity Center discusses the peasence of cones in Tobleria bicuspis, a Voltziales Conifer from the Earliest Permian Jambi Palaeoflora of Jambi Province in Sumatra, Indonesia.

The Jambi Palaeoflora comprises a number of coalified plant fossils excavated from outcrops of the Mengkarang Formation along tributaries of the Merangin River. These deposits are thought to be between 296.77 and 296.14 million years old, and were laid down in a tropical forest about 15° north of the Equator. Eighteen samples were used in the study, seventeen of which were collected in 1925 by Wilhelmus Jongmans and Walther Gothan, plus one specimen collected from the same area in 2006.

Map of the Bangko area showing the outcrops of the Mengkarang Formation along the distributaries of the Merangin River where Tobleria bicuspis was found. Van Waveren (2019).

Examination of the samples found that they had cones made up of tightly packed bicuspid (double tipped) scales (typical for cone-bearing members of the Voltziales). The most intact of these (from sample 45311, a slab of light beige, finely banded, tuffaceous mud collected along the Karing River by Jongmans and Gothan) is 24 mm long, and 8-9 mm wide at the base, tapering to about 4-5 mm, although this is not a complete cone, with the base being broken so that it would have originally been somewhat longer.

The three cones from sample 45311: (A) cone C1, (B) Tobleria bicuspis right edge of cone C2 fragment showing bicuspid scale and seeds (C) Tobleria bicuspis cone C3 fragment showing bicuspid scale. Arrows 1–4 in Figure (A) indicate scales in side view, arrow 5 indicates the cone axis. The arrow in Figure (C) indicates a bifid scale. Scale bars: 10 mm (A); 2,5 mm (B); 5 mm (C). Van Waveren (2019).

Each of the scales is about 3 mm wide and 5 mm long, and has two, linked 'fertile utits' (seeds) on its inner surface. These 'fertile units' vary somewhat in shape, from adpressed hemispheres, to heart-shapes attached at the central and narrowest points, to paired almond shapes. These vary in length between 0.6 and 2.6 mm, and in width between 0.4 and 1.6 mm.

Details of dispersed seeds, scales and fertile scales: (A) paired seeds with double wall (sample 45311C) (B) paired seeds with triangular micropylar protrusion (sample 45311 E) (C) detail of triangular micropylar protrusion from paired seeds (sample 45311 E) (D) heart shaped paired seeds/ovules (sample 45311 D) (E) heart shaped paired seeds/ovules (sample 45311 B) (F) juxtaposed almond shaped seeds/ovules (sample 45311 B) (G) bicuspid scale (sample 45311 Aa) (H) bicuspid scale (sample 45311D) (I) bicuspid scale (sample 45471) (J) bicuspid scale with contour of two seeds/ovules (sample 45315) (K) bicuspid scale with darker organic contour of seed (sample 45310) (L) bicuspid scale with heart shaped contour of seeds/ovules (sample 45471). Van Waveren (2019).

Van Waveren notes that four Conifer groups were producing cones by the end of the Permian, the Cordaitanthales, the Ferugliocladales, the Dicranophyllales, and the Voltziales, as well as three non-Conifer groups, the Cycadalean, the Gnetaleans, and the Peltaspermaleans. The first Cycad cones appear in the Early Permian, but are quite distinct from Conifer cones, with their seeds located laterally to (sideways of) their cones, the earliest known Gnetalean cones appear in the Late Permian of China, and are spear-shapes, with single seeds, and the Peltaspermaleans have very rounded scales. The scales and seeds of the Cordaitanthaleans form a distinct wing shape, while the seeds of the Ferugliocladales are attached to the cone axis rather than the scales, while the scales of the Cheirolepidiales are triple in form, but encase a single seed. The cone-bearing Voltziales, in contrast typically have bicuspid cone-scales and double seeds, leading Van Waveren to conclude that the placement of Tobleria bicuspis in this group is quite safe taxonomicaly.

Reconstruction of Tobleria bicuspis. Scale bar is 1 cm. Van Waveren (2019).

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Zamia paucifoliolata: A new species of Cycad from the Pacific coastal forests of Valle del Cauca, Colombia.

Cycad’s are of particular interest to botanists and horticulturalists due to their unique evolutionary heritage; they are Gymnosperms (non-flowering Seed Plants), members of the group that includes Conifers and Ginkos, but among the closest non-flowering relatives of the Angiosperms (Flowering Plants). They large attractive plants, superficially resembling Palms, but producing large and often brightly coloured strobili, structures intermediate between cones and flowers; these are often pollinated by Beetles or Thrips. Cycads are thought to have originated during the Permian, and became dominant Plants in many ecosystems during the Jurassic and Cretaceous, but suffered heavily during the End Cretaceous Extinction, and there are about 330 species surviving today, predominantly in the Southern Hemisphere, most of which diversity is thought to have arisen from a post-Cretaceous radiation. Members of the genus Zamia are found from the southern United Stated though Central America and the Caribbean as far south as Bolivia. Zamias are deciduous shrubs, often growing from a subteranean rhizome (horizontal stem).

In a paper published in the journal Phytotaxa on 28 December 2018, Michael Calonje of the Montgomery Botanical Center, and Cristina López-Gallego and Jonatan Castro of the Universidad de Antioquia, describe a new species of Zamia from the Pacific coastal forests of Valle del Cauca, Colombia.

The new species is named Zamia paucifoliolata, in reference to the small number of leaflets on its leaves (no more than 18 on leaves up to 285 cm in length). The plant grows from an underground rhizome (buried horizontal stem) which produces erect leaves, singularly or in pairs, at regular intervals. Zamia paucifoliolata was found growing in a coastal forest with an average annual rainfall of 7000-7700 mm, making it one of the wettest terrestrial environments on the Earth. The species was found growing at only two localities, roughly 5 km apart, with a total known range of less than 3 km², for which reason Calonje et al. consider it to be Endangered under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species.

Zamia paucifoliolata in its natural habitat at the type locality. (A) Middle leaflets collected from plants at different stages of development. (B) Juvenile plant. (C) Adult plant with seed strobilus, showing yellow clay soils in which the species grows. (D) Adult plant in habitat with Jonatan Castro (left) and Michael Calonje (right). (E) The largest leaf yet observed for this species, measuring 285 cm long and carrying 18 leaflets. Calonje et al. (2018).

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Understanding the extraordinary success of Pines.

Gymnosperms (Non-flowering Seed Plants) first arose in the Devonian, and by the Mesozoic had come to dominate almost all terrestrial ecosystems. Angiosperms appeared some time in the Jurassic or Early Cretaceous, and appear to have initially been minor components of the terrestrial flora, but began to rapidly diversify in the Middle Cretaceous, and by the end of that period had become the dominant group of Plants on Earth, leading to the extinction of formerly successful groups such as the Bennettitales and Seed Ferns, while other groups, such as the Gingkoes, Cycads, and Tree Ferns underwent huge declines, and only survive as relict groups with a few remotely scattered populations today. One Gymnosperm group, however, has done remarkably well in an Angiosperm-dominated world. The Conifers, and in particular the Pines, Pinus spp., underwent a significant diversification at the same time as the Angiosperms, and apparently thrived in the environment that these Plants created. Pines have continued to be a success story in the post-Cretaceous world, and have undergone a series of extra expansions as terrestrial ecosystems became dominated by first Grasses and then Humans.

In a paper published in the journal Ecology and Evolution on 21 September 2018, Surendra Singh of the Central Himalayan Environment Association, Inderjit of the Centre for Environmental Management of Degraded Ecosystems at the University of Delhi, Jamuna Singh of the Department of Botany at Banaras Hindu University, Sudipto Majumdar, also of the Centre for Environmental Management of Degraded Ecosystems, Jaime Moyano and Martin Nuñez of the Grupo de Ecologia de Invasiones at the Universidad Nacional del Comahue, and David Richardson of the Centre for Invasion Biology at Stellenbosch University, examine the reasons for the extraordinary rise of the Pines, and their continued success in modern, Human-dominated landscapes.

Pines in the Northern (native) and Southern (nonnative) Hemispheres. (a) Pinus longaeva in the White Mountains, California, USA; (b) Pinus contorta, southern California, USA; (c) Pinus halepensis, southern France; (d) Pinus pinaster, Andalucía, Spain; (e) Pinus contorta, colonising subalpine meadow, Sequoia National Forest, California, USA; (f) Pinus roxburghii in the Himalaya, Uttarakhand, India; (g) Pinus contorta invading Patagonian steppe vegetation, near Bariloche, Argentina; (h) Pinus pinaster invading fynbos shrubland, Western Cape, South Africa. David Richardson and Inderjit in Singh et al. (2018). 

The rise in Angiosperms during the Cretaceous was associated with a changed fire regime; put simply forests of Angiosperm trees were able to survive frequent forest fires while most Gymnosperms were not, so that any Gymnosperm living in an Angiosperm-dominated woodland had a good chance of being killed by each fire cycle, while the Angiosperms surviving it simply grew back. Pines, however, did not suffer this problem, with the genus splitting into two subgenera with different strategies for surviving fire early in the group’s history.

Members of the subgenus Diploxylon, sometimes known as ‘Hard Pines’, are fire adapted, having evolved in a number of ways that help them cope with frequent fires. Firstly these trees have thick, fire resistant bark, which protects the vascular tissues of the trunk (cambium) from heat damage; a 15 mm thick bark layer can protect the interior of the tree against external temperatures as high as 400°C for as long as 3 minutes (generally long enough for any available fuel to be consumed at these temperatures). Secondly these Pines produce a large number of long, flammable needles, which drop to the ground around the trees, causing any fires to burn rapidly and intensely, i.e. in a way that the Pine can cope with, but any competitor Plants nearby might find challenging. In some Pine species these needles are retained on the branches, resulting in an intense fire in the canopy, something which again is likely to prove challenging to competitors. In such trees the Pine seeds are typically also retained in cones within the canopy, with the cones only opening and shedding the seeds after being exposed to fire, presenting the new seeds with soil enriched by the forest fire and cleared of competitors.

Pines of the subgenus Haploxylon (or Strobus), sometimes known as ‘Soft Pines’, in contrast, survived the evolution of new fire regimes in the Cretaceous by simply avoiding Angiosperm forests completely, evolving traits that enabled them to survive in areas such where Angiosperms could not. These Pines also have thick bark, though in this instance it is used as an insulator against the cold, with such trees able to survive temperatures as low as -90°C, and have closable stomata which enable them to survive in very dry conditions. These Pines developed an ectomycorrhizal relationship (relationship in which the root is surrounded by a sheath of Fungi) with Basidiomycete Fungi by the Middle Eocene, giving them an additional advantage in colonising cooler northerly and high altitude environments, as these Fungi are more tolerant of such conditions than the arbuscular mycorrhizal relationship (relationship in which Fungal fibres penetrate the root) most other Plants form with Ascomycete Fungi; to date only one group of Angiosperms have formed a similar relationship with the Basidiomycetes, the Fagales (Beeches, Oaks etc.).

These adaptations have enabled Pines to survive a number of new conditions that have arisen in the post-Cretaceous world, such as the evolution of savanna ecosystems, grasslands with an annual fire cycle, impossible to colonise for trees without adaptations to fires, or the Pleistocene glaciations, during which cold-adapted Pines were able to survive in refugia unavailable to less hardy Plants, giving them a considerable advantage when the glaciers cleared, opening up large areas for colonisation by the surviving tree species.

The appearance of Humans has created a number of new opportunities for Pines, firstly through the spread of slash-and-burn agriculture, which sweeps away other tree species, creating opportunities for fire-adapted Pines, and then by the active planting of Pines for their long, straight trunks and excellent timber. Humans have carried Pines to many new environments, particularly in the Southern Hemisphere, where they have often become highly invasive in ecosystems unused to them. Pines have been able to invade a number of Southern Hemisphere ecosystems that were formerly treeless, such as the arid Patagonian steppe, South African fynbos, and the grasslands and shrublands of New Zealand, where dry conditions and periodic fires had excluded native tree species. The ability of Pines to survive at high altitudes has also given them a novel advantage in the Southern Hemisphere, where no other trees are adapted to do this, for example in the native treeline is found at 1950 m above sea level in Chile, and in New Zealand it is even lower at 1350 m, but in both areas Pines can climb as high as 4000 m above sea level, giving them the opportunity to colonise large areas of mountainside formerly free of trees.

Key drivers and responses during the evolution of pines. Gymnosperms originated in the Devonian (350 Myr ago), but Pines originated ~150 Myr ago. Oval shapes indicate environmental filters, red ovals for Diploxylon and blue ovals for Haploxylon Pines. The presence of different groups is represented by numbers: (1) Gymnosperms; (2) Pines prior to diversification; (3) Diploxylon; (4) Haploxylon; (5) Angiosperms; (6) C3 Grasses; (7) C4 Grasses. Solid red ovals indicate fire as a driver, and solid blue ovals denote extreme environments as drivers. Dashed red or blue ovals indicate the impact of humans. Angiosperms, mainly shrubs and herbs, appeared as understorey ruderals in the Late Cretaceous (65–145 Myr ago) and later proliferated in response to novel fire regimes. This resulted in the shift of community structure as slow-growing Gymnosperms were replaced by fast-growing Angiosperms, resulting in the decline of Gymnosperms except Conifers. Changes in the climate in the Miocene (5–24 Myr ago) led to the replacement of woodlands with grasslands dominated by C4 species. Highly flammable C4 grasses became abundant in open areas with higher light availability. Pinus has shown remarkable adaptability to highly flammable ecosystems, including frequently burned C4 grasslands. The timing of Angiosperm evolution overlaps with the origin and diversification of pines into Diploxylon and Haploxylon taxa. Haploxylon taxa are fire-avoiding and occur in drier and colder regions, whereas Diploxylon taxa are fire-adapted and occur in more productive environments at subtropical and temperate latitudes. Diploxylon Pines evolved to adapt to fire and codominate with Angiosperms in some more productive regions outside tropical rain forests. Singh et al. (2018). 

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Ginkgo hamiensis: A new species of Ginkgoalean from the Middle Jurassic of eastern Xinjiang, China.

Ginkgoes, Ginkgoales, are Gymnospermous Plants (plants which produce seeds without coverings), with distinctive bilobed leaves. They first appeared in the Permian, but did not become an important group until the Middle Jurassic, when they became a dominant group in many parts of the world, before being replaced in most areas by Flowering Plants in the Middle Cretaceous. Only a single genus, Ginkgo (which first appeared in the Triassic) survived the End of the Cretaceous, with a single species Ginkgo biloba, surviving today.

In a paper published in the journal Acta Geologica Sinica in February 2017, Wang Zixi, Sun Fankai, Jin Peihong, Chen Yingquan, Chen Jingwei, Deng Peng, and Yang Guolin of the School of Earth Sciences & Key Laboratory of Mineral Resources in Western China at Lanzhou University, and Sun Bainian, also of the School of Earth Sciences & Key Laboratory of Mineral Resources in Western China at Lanzhou University, and of the Key Laboratory of Petroleum Resources of the Chinese Academy of Sciences, describe a new species of Ginkgo from the Xishanyao Formation of the Turpan–Hami Basin in eastern Xinjiang, China.

The new species is named Ginkgo hamiensis, meaning 'from Hami' in reference to the location where it was found, the Sandaoling Coal Mine in Hami.The species is described from a single specimen, comprising two pollen (male) cones and a number of leaves. Male cones are extremely rare in the fossil record, with only three previously described specimens assigned to the genus Ginkgo. These cones are long and cylindrical in shape, and provide an insight into the genus at an important time in its evolutionary history.

Pollen cones of Ginkgo hamiensis (arrows). Scale bar is 1 cm. Wang et al. (2017).

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