Plant defense against herbivory in the context of "Thorns, spines, and prickles"

Nectar is a viscous, sugar-rich liquid produced by plants in glands called nectaries, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide herbivore protection. Common nectar-consuming pollinators include mosquitoes, hoverflies, wasps, bees, butterflies and moths, hummingbirds, honeyeaters and bats. Nectar is an economically important substance as it is the sugar source for honey.

Nectar is also useful in agriculture and horticulture because the adult stages of some predatory insects feed on nectar. For example, a number of predacious or parasitoid wasps (e.g., the social wasp species Apoica flavissima) rely on nectar as a primary food source. In turn, these wasps then hunt agricultural pest insects as food for their young.

Medicinal plants, also called medicinal herbs, have been discovered and used in traditional medicine practices since prehistoric times. Plants synthesize hundreds of chemical compounds for various functions, including defense and protection against insects, fungi, diseases, against parasites and herbivorous mammals.

The earliest historical records of herbs are found from the Sumerian civilization, where hundreds of medicinal plants including opium are listed on clay tablets, c. 3000 BC. The Ebers Papyrus from ancient Egypt, c. 1550 BC, describes over 850 plant medicines. The Greek physician Dioscorides, who worked in the Roman army, documented over 1000 recipes for medicines using over 600 medicinal plants in De materia medica, c. 60 AD; this formed the basis of pharmacopoeias for some 1500 years. Drug research sometimes makes use of ethnobotany to search for pharmacologically active substances, and this approach has yielded hundreds of useful compounds. These include the common drugs aspirin, digoxin, quinine, and opium. The compounds found in plants are diverse, with most in four biochemical classes: alkaloids, glycosides, polyphenols, and terpenes. Few of these are scientifically confirmed as medicines or used in conventional medicine.

Coumarin (/ˈkuːmərɪn/) or 2H-chromen-2-one is an aromatic organic chemical compound with formula C₉H₆O₂. Its molecule can be described as a benzene molecule with two adjacent hydrogen atoms replaced by an unsaturated lactone ring −(CH)=(CH)−(C=O)−O−, forming a second six-membered heterocycle that shares two carbons with the benzene ring. It belongs to the benzopyrone chemical class and is considered a lactone.

Coumarin is a colorless crystalline solid with a sweet odor resembling the scent of vanilla and a bitter taste. It is found in many plants, where it may serve as a chemical defense against predators. While coumarin is not an anticoagulant, its 3-alkyl-4-hydroxy derivatives, such as the fungal metabolite dicoumarol, inhibit synthesis of vitamin K, a key component in blood clotting. A related compound, the prescription drug anticoagulant warfarin, is used to inhibit formation of blood clots, deep vein thrombosis, and pulmonary embolism.

Nicotine is an alkaloid found primarily in plants of the nightshade family, notably in tobacco and Duboisia hopwoodii. In addition to extraction from tobacco, it is synthesized. Nicotine is used recreationally for its stimulant and anxiolytic effects. In tobacco leaves, nicotine constitutes about 0.6–3.0% of the dry weight, and smaller, trace quantities occur in other Solanaceae crops such as tomatoes, potatoes, and eggplants. In pure form, nicotine is a colorless to yellowish, oily liquid that readily penetrates biological membranes and acts as a potent neurotoxin in insects, where it serves as a antiherbivore toxin. Historically, it was widely used as an insecticide, and its structure provided the basis for synthetic neonicotinoid pesticides.

In humans, nicotine acts primarily as a stimulant by binding to and activating nicotinic acetylcholine receptors (nAChRs) in the central nervous system and peripheral tissues. This results in the release of neurotransmitters such as dopamine, acetylcholine, and norepinephrine, producing effects including increased alertness, reduced anxiety, and mild euphoria. Nicotine is typically consumed through tobacco smoking, vaping, or other nicotine delivery systems. An average cigarette yields about 2 mg of absorbed nicotine, a dose sufficient to produce reinforcement and dependence while remaining far below toxic levels.

Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrates, or other pests that affect plant health by eating plant tissues and causing injury that may admit plant pathogens. The study of plant disease is called plant pathology.