Preserved gum in an Early Cretaceous Welwitschiacean.
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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.