According to Jataka Tales (the stories that tell the life history of Gautama Buddha), Jeevaka, the legendry physician treated Buddha. He also treated King Bindisara, the father of Emperor Ashoka.
As Jeevaka completed his studies at the Ashram of his Guru, Aatreya, he was asked to present a plant with no medicinal value as his Guru Dakshina. Gurudakshina is the gift of offering a disciple gives to his teacher when his education is completed.
Jeevaka searched the whole of Sarlaka Mountain to find such a plant with no medicinal value. He returned to his teacher empty handed and told his guru that he was not able to give him a guru dakshina. He also said to his teacher that not only the plants, but also the smell, sunlight, and sound originating from the stream that passes mildly by are filled with medicinal power. Some heal physical ailment of humans, while others cure ailments of animals or plants. Some are good for curing any mental condition.
Then Guru Aatreya smiled at him and said “everything in this world has its own significance”.
This is the basis of Ayurveda. When you think about Ayurvedic medicinal plants, think that every plant on earth is a medicinal plant.
The thing is to identify the method to identify and extract that medicinal power for appropriate use.
Same species of plants growing at different places can have different medicinal values. For example the plants growing in Himalayas will not be the same as the ones growing in Agastya hills of Kerala. The natural habitat, climate, available minerals, presence of other plants and trees, etc have influence on the medicinal properties of plants. This may not be primarily identifiable, but it is a fact there is at least a minor difference in the medicinal property of same species plants growing in different locations.
Cultivation of medicinal plants has picked up speed. In India and in places outside India there is large-scale cultivation of medicinal plants. Using of chemical fertilizers is a strict no-no for medicinal plant cultivation. It is also to be noted it is not possible to recreate the natural surroundings at which a medicinal plant grows in a different location.
Keep the story of Jeevaka and his Teacher, Guru Aatreya in mind, whenever you hear the term Ayurvedic medicinal plants or Ayurvedic medicinal herbs.
The following is a (naturally) incomplete list of medicinal plants and herbs used in Ayurvedic treatment.