Hinduism and six traditional sacred trees

In Hinduism  there exists a close relationship with tress and plants. As a matter of fact in this religion all living things are believed to be sacred in their own ways.  Besides the fact that some trees have medicine values,  because of their association with the deities in the Hindu mythology, people consider them holy or unique and worship them. The following are the trees or plants that have some links with the almighty.
Banyan Tree  www.reddit.com
The Banyan tree, (in Tamil: Arasa maram; name comes from Gujarati Baniya) is one of the  most important trees  in Hindu religion and one can find them in many Hindu temples.  The Gujarati traders used to do business with the European merchants  centuries ago under the Banyan tree; hence the name. Ficus religiosa or sacred fig is a species of fig native to Indian subcontinent, south-west China and Indochina. Frequently referred to as ashwattha tree (in India and Nepal).

As a matter of fact in any rural areas, particularly in Tamil Nadu one can find a small stone idol of  God Ganesa or some other goddess under the banyan tree. The goddess is supposedly the village deity, guarding  the village and the people living there.   The tree, as a whole, is also widely worshiped  by people as, it is  believed, to be  the abode of Lord Krishna.  In the Bhagavad Gita, Krishna says, "I am the Peepal tree among the trees, Narada among the sages, Chitraaratha among the Gandharvas, And sage Kapila among the Siddhas." Young women seeking fertility worship the tree regularly for a particular period of time and pregnant women also offer prayers regularly for event less and  safe  delivery of the baby.  The tree offers  a large area of shade to weary travelers and villagers especially in the summer time. More often than not, the local village council or Panchayat members meet and discuss the affairs of local village administration as well as fringe areas in the cool shadows of the huge banyan tree to redress the civic problems being faced by the villagers.  The Ficus religiosa tree is considered sacred by the followers of Hinduism, Jainism and Buddhism. 
Parijat tree at Kintoor, Barabanki, UP, India. en.wikipedia.org
The Parijaat Tree, is believed to be a sacred baobab tree in the village of Kintoor, near Barabanki, in the state of Uttar Pradesh.  It is a male tree of the baobab genus. This tree  is mentioned in the great epic Mahabarata and is purported to have been brought from heaven by the great archer Arjuna. Kunti Devi used to offer the flowers from the tree to Lord Shiva as part of her regular prayer. The tree is believed to be  a Kalpavriksha - a unique  wish granting tree that fulfills the wishes and aspirations of the  people who come and pray before it with reverence. 

The Ashoka tree, considered to be holy in Hinduism,  Buddhism and Jainism, is a small evergreen rain-forest tree that produces  beautiful and fragrant red and yellow flowers. One can find this tree in many gardens in India  The tree used to be a centre piece in every palatial garden in India.   The Hindu temples and Buddhist monasteries have the symbol of the Yakshi, a female deity standing with her foot on the trunk and her hand holding the branch of an Ashoka tree. It is found  in Central and Easter Himalayas and in the Western Ghats. In the great Epic Ramayana the messenger of Sri Rama great Hanuman saw, for the first time, the consort of the  lord Sri Sita (who was in exile) under the Asoka tree in the Asoka Vanam of Lanka kingdom.  Ashoka  tree is a well-known tree of India. In Sanskrit, Ashoka means without grief or the one who gives no grief.

The Sandalwood tree (the genus Santalum) is widely used in Buddhism and Islam besides  Hinduism. In Sufi tradition, sandalwood paste is applied on the Sufi’s grave by the disciples as a mark of devotion. It is widely practiced particularly among the Indian Subcontinent Muslim disciples. This fragrant tree is closely associated with  Lord Dharukavaneshwara. Sandal paste is widely used in all Vaishnava temples, in particular, Sri Krishna temples of Kerala. The wood is sacred in all temples of  Subramaniya or Karthkeya as well. Santhana Abiskegam - anointing using sandalwood water is common in many temples of Tamil Nadu.  At temples, preparation of the paste is entrusted only with the priests, as part of their religious duty. Because the paste will be applied on the main idol, and it should be prepared with utmost care, devotion or bakthi. 

According to some Buddhist traditions, sandalwood is considered to be of the padma (lotus) group and attributed to Amitabha Buddha. Sandalwood scent is believed by some to transform one's desires and maintain a person's alertness while in meditation.

Many devotees after tonsuring their head as part of their prayer, at temples like Tirupathi (Andhra), Palani Thiruchendur (Tamil Nadu), etc., apply the sandalwood paste with water on the  freshly shaved head. Sandalwood paste has medicinal properties and is good to cool the body heat and give relief to skin rashes and skin pricks.  Devout Hindus use the sandal paste as a mark on the  foreheads.
Ficus religiosa (peepal tree), Leaves and trunk of a sacred fig.
Note the distinctive leaf shape.

A huge Peepal tree in Mirzapur, Uttar Pradesh,en.wikipedia.org
The Peepal tree, also known as  the Sacred Fig or the Bodhi Tree is  yet another tree of much significance in Hinduism. It was under the a Peepal tree, King Siddartha  (Lord Buddha) had meditated and gained enlightenment. Later he chose the path of of renounciation, giving up his princely, luxurious life for the sake of humanity and their sufferings. Hence it is more sacred to the Buddhists than others. The leaves, etc have extensive medicinal value and are widely used in traditional Ayurvedic medicine to treat  Jaundice,  epilepsy, gastric problems, asthma, diabetes, diarrhea, inflammation and infections and sexual disorders. It is also  used to cure certain  sexual disorders.
Tulsi madam or vridavan. ykantiques.com

The Tulsi or Tulasi (Ocimum tenuiflorum) plant or Holy basil is a widely used sacred plant in Hindu belief. Hindus regard it as an earthly manifestation of the goddess Tulsi; she is regarded as a great worshiper of the god Vishnu.  Shri-Tulsi is  synonymous with  Lakshmi Goddess of wealth and a consort of Lord Vishnu. The offering of its leaves is mandatory in ritualistic worship of Vishnu and his forms like Krishna and Vithoba or Rama. In Hindu mythology, the Tulsi plant
Tulsi plants. www.remedyspot.com

(Tulsi known as-Vaishnavi -"belonging to Vishnu,"or Vishnu Vallabha - "beloved of Vishnu")   is regarded  as the holiest of all plants and is found at a  point between heaven and earth.

Hindu homes  have Tulsi plants growing in front of or in the rear of their home. Some people have Tulsi Madam (also called Vrindavan)  in the central courtyard.  It is a common feature in all Brahmin homes  in the Agraharams of South India in those days. The plant is kept in the houses  for religious and medicinal purposes.  Sacred places where they are grown are also known as Vrindavan - grove of Tulsi.

Tulsi is sacred to Sri Krishna and Sri Rama, avatars of Sri Vishnu. Garlands made of hundreds of  tulsi leaves are offered to  main deities in Vaishnava temples. So is  Tulsi Thertham (holy water mixed with Tulsi leaves) by the temple priest to the devotees. According to Vaishnava tradition,  use of Japa malas (a string of Hindu prayer beads) made from Tulsi stems or roots called Tulsi Malas (important symbol of the initiation). Such Tulsi  

An altar with tulsi plant for daily worship in a courtyard in India.en.wikipedia.org
Set of Japa mala(payer mala), made from Tulasi wood, with head bead in foreground.en.wikipedia.org
alas are believed  to be auspicious for the wearer,
because  Vishnu or Krishna  will protect him in times of trials and tribulations. As for the deities, such Malas enhance the sanctity of the main shrines.