Common Hawthorn (Crataegus monogyna Jacq.)
Family: Rosaceae

The Common Hawthorn is a shrub or small tree 5–14 m tall, with a dense crown. The bark is dull brown with vertical orange cracks and the younger stems bear sharp thorns, 1 to 1.5 cm long. The leaves are 2–4 cm long, obovate and deeply lobed, sometimes almost to the midrib, with the lobes spreading at a wide angle. The upper surface is dark green above and paler underneath.
The hermaphrodite flowers are produced in late spring (May to early June in its native area) in corymbs of 5-25 together; each flower is about 1 cm diameter, and has five white petals, numerous red stamens, and a single style; they are moderately fragrant. The flowers are pollinated by midges, bees and other insects and later in the year bear numerous haws. The haw is a small, oval dark red fruit about 1 cm long, berry-like, but structurally a pome containing a single seed.

Geographic Distribution. Hawthorn is native to Europe, northwest Africa and western Asia. It has been introduced in many other parts of the world where it can be an invasive weed.
 

Habitat. It spreads readily by seed into woodlands and open fields, often creating a dense, thorny thicket.  Its abundant red berries are attractive to birds and other animals, which help spread this tree far beyond where it is planted.
 

Chemical composition. Hawthorn fruits, leaves, and flowers contain a number of chemical constituents, such as flavonoids (0.1%-1% in fruits, 1%-2% in leaves and flowers), oligomeric proanthocyanidins (OPCs, 1%-3% in fruits or leaves with flowers), triterpene acids (0.5%-1.4% in fruits), organic acids (2%-6%), sterols, and trace amounts of cardioactive amines.
Hawthorn berries acuumulate such macro- and microelements as: Ca, K, Mg, Fe, Mn, Cu, Zn, Cr, Se, I.
The chemical composition of flowers and fruits is quite different, but nonetheless both are used for treating cardiovascular system diseases.

Medicinal use. Hawthorn is an extremely valuable medicinal herb. It is used mainly for treating disorders of the heart and circulatory system. Western herbalists consider it a 'food for the heart', as it increases the blood flow to the heart muscles and restores normal heart beat. This effect is brought about by the presence of bioflavonoids in the fruit, these bioflavonoids are also a strong antioxidant, helping to prevent or reduce degeneration of the blood vessels. The fruit is antispasmodic, cardiac, diuretic, sedative, tonic and vasodilator. Both the fruits and flowers of hawthorns are well-known in herbal folk medicine as a heart tonic and modern research has borne out this use. The fruits and flowers have a hypotensive effect as well as acting as a direct and mild heart tonic. They are used in the treatment of a weak heart combined with high blood pressure,.  Additionally they can be used to treat a heart muscle weakened by age,  inflammation of the heart muscle, arteriosclerosis, and for nervous heart problems.
Animal and laboratory studies report hawthorn contains antioxidants, including oligomeric procyandins (OPCs, also found in grapes) and quercetin. Antioxidants are substances that destroy free radicals -- compounds in the body that damage cell membranes, tamper with DNA, and even cause cell death. Free radicals occur naturally in the body and grow in number as we age. Environmental toxins (including ultraviolet light, radiation, smoking, some medicines, and air pollution) can also increase the number of these damaging particles. Free radicals are believed to contribute to the aging process (such as wrinkling), as well as the development of a number of health problems, including cancer and heart disease. Antioxidants found in hawthorn may help stop some of the damage from free radicals, especially when it comes to heart disease.

More information from University of Maryland Medical Center about hawthorn can be found here