Trees (rukkha) are tall plants usually with a thick woody stem from which branches covered with leaves grow. Being a sensitive and observant person, and spending much of his time in forests, the Buddha developed a great appreciation for and knowledge of trees.
Some of the structural components of trees that he mentioned include the trunk (khandha), the periderm or outer bark (papaṭikā), the phloem or inner bark (taca), the sapwood (pheggu), the heartwood (sāra), branches (sākhā), twigs (pasākha) and leaves (paṇṇa) (M.I,193-6).
He was aware of the different root systems; large woody roots (mūla), tap roots and lateral roots (malāni adhogamāniyāni tiriyaṅgamāni), feeder roots and hair roots (usīranāḷi). He also understood that these roots absorbed moisture and nutrition from the soil, and that the sap (ojā) moves upwards through the trunk into the branches (S.II,87-8).
Many of the Buddha’s discourses also indicate that he had a particular affection for trees. As a young man he had his first deep spritual experience while sitting in the shade of a rose apple tree (M.I,246).
He taught that it is a good deed to plant shade trees along the sides of roads (S.I,33). He considered forests to be good places to meditate in. Very often he would say to his disciples: ‘Here are the roots of the trees, here are the empty places. Meditate! That is my instruction to you.’ (M.I,46).
It was said of him that he ‘seeks lodgings in the forest, in the depths of the jungle, in quiet places.’ (D.III,38). To the Buddha, his Dhamma was so self-evident that on one occasion he pointed to the nearby trees and said: ‘Even these great sal trees would embrace the Dhamma if they could comprehend, how much more so human beings?’ (A. II, 193).
The Buddha said of a kindly, hospitable person that he was ‘like a great banyan tree growing on the side of a road that welcomes weary travellers with its cool shade and soothes their tiredness.’ (Ja.VI,526). The Milindapañha says we should try to be like a tree:
‘As a tree makes no distinction in the shade it gives, like this, the meditator should make no distinction between any beings, but develop love equally to thieves, murderers, enemies and to himself or herself.’ (Mil.410).
Then, when it breaks into blossom in the spring, at the end of winter, you will remember me and say: “Such was my daughter’s beauty.”’ (Ja.V,302). The Buddhacarita compares spiritual practice to a tree ‘whose fibers are patience, whose flowers are virtue, whose boughs are awareness and wisdom, which is rooted in resolution and which bears the fruit of Dhamma.’