Digestive agents

Throughout the ages, plants have proved to be precious sources to relieve and aid digestion. Thanks to their eupeptic,  antispasmodic or antacid properties, they are conducive to appetite, relieve cramp or counter acidity caused by anxiety or eating excesses.  
Angelica (Angelica archangelica L.) is the main plant for digestion and intestinal spasms. Also appreciated as a general tonic and to combat fatigue, its properties are said to have been revealed to man by an angel. Also, candied angelica stems are delicious sweets. Balm (Mellissa officinalis L.), which is more widely known, relieves spasms and settles the stomach.  

Respiratory agents

Many plants in this category are rich in aromatic substances providing essential oils and are suitable for the entire respiratory tract. The demulcent properties of other plants will alleviate disorders of the throat or the skin.
Plantain (Plantago major L.), a common garden plant whose Latin name means "plant that acts", relieves throat ache, alleviates skin disorders, conjunctivitis and pain caused by insect bites. It is almost always found near colonies of stinging nettle whose itch it soothes.
The Romans used thyme (Thymus vulgaris L.) to purify their homes. In the Middle Ages, it symbolised courage.  Appreciated as a condiment, it is a natural antiseptic that is used to prevent winter illnesses and also has relaxing properties.
Lavender (Lavendula officinalis L.) is effective to counter respiratory infections and its properties will also smooth burns and muscle cramp.  

Circulatory agents

Any human activity, whether physical, spiritual, emotional or creative, puts a greater or lesser strain on the heart. Since the days of antiquity, physicians such as Pliny, Galen and Hippocrates prescribed plants to regulate blood circulation.
Hawthorn (Crataegus monogyna L.), which etymologically means white thorn, has many medicinal cardiac properties, in particular to alleviate palpitations and hypertension. It is said that its thorns served to form Christ's crown prior to his crucifixion. 

Yarrow (Achillea millefolium L.) owes its Latin name to a legend according to which Achilles, on the advice of the Centaurs, used it to treat his wounded warriors. Up to the 19th century, soldiers benefited from its scarring and disinfecting properties, hence its name "the military herb".   
Circulatory agents also include hop (Humulus lupulus L.) and woodruff (Galium odorata L.), both of which are in fact well known in these parts as they are included highly appreciated beverages: beer and maitrank. 

Neurological agents

The vegetable kingdom brings forth great treasures but extreme caution is in order to appreciate all its benefits. Herbal medicine calls for considerable preparation and exact dosages. Certain components of one and the same plant will be usable whereas others must be avoided. For instance, simple contact with a poisonous species may sometimes cause serious disorders.
Purple foxglove (Digitalis purpurea L.), also known as Lady's Glove, is a highly efficient cardiac tonic thanks to its extract digitalin, but proves highly toxic in its natural state. Ingestion of its fresh leaves will lead to serious poisoning and may at times be fatal. 

The leaves of common ivy (Hedera helix L.) are beneficial when used externally against ulcers and corns and they are also considered to be beneficial against respiratory tract infections. However, skin contact leads to allergies in some sensitive people and ingestion of ivy leaves in high doses causes destruction of the red corpuscles.  Its berries are even more dangerous, in particular for children who will suffer digestive problems with vomiting and diarrhoea. 
The golden rule to avoid any adverse effect is therefore to stay away from using medicinal plants and always have recourse to the opinion of a medicinal plant specialist.