Following the classification of Bentham and Hooker if simplest and before to identify any plant, remembering the characteristics of plant parts is much helpful.

The most reliable way to identify a wild plant is (after making sure you have the correct permits/permissions for that country from the landowner and the nature conservation authorities), taking a voucher (small sample of the plant, as many parts -root, stem, leaf, flower, seed) as possible with you to a quality national herbarium and compare it to vouchers there, preferably with help from a specialist in plants from that region. I hear from people in herbaria/botanic gardens that an amazing number of plant vouchers they see are incorrectly identified by people just making their best guess, so checking against authorities is never a bad idea. But you have to be careful with legal issues about picking and moving wild plants and sometimes it may be illegal.

Thanks for adding the valuable information.

One can identify the plant by its ethanobotanical, ethnomedicinal, ethnopharmacological database. Also by discussing the traditional uses of the plant by the tribes of the respective region. Pharmacognostic study also helps in identification of the plants.

Firstly you should have sufficient knowledge about the flora of the area in question. If the plant does not matches with any of the reported species in the area, then it becomes a candidate for further attention. Then you should try to ascertain the identity of the plant by correlating it with other species in the area, it might be a different variety of the available species. If both the things are negative, then proceed for a authentication from the appropriate authority in that area itself because they are the ones who know the best about the flora of that area. If they are also not able to identify the plant, then you can consider it as a wild/ unknown plant form that area only as it might be a major species in some areas nearby also.

Deposit the specimen with the authorities in that area for future reference and further identification at their end. Then proceed and approach higher authentification authorities for proper identification like BSI, NBRI, CIMAP etc.

Firstly it is needed to make a herbarium of that wild species.Then you need to identify this species with the help of Devid Prain's Book " Bengal Plants". if it is matched then it is ok otherwise this herbarium needed to send National Herbarium for cross verification & identification.You will then easily identify this wild species with the database of that National Herbarium .

I've been reading about DNA barcoding as a means of plant identification.

I think one should first try to place the wild plant in a particular family based on the morphological features. After this you can compare the her-barium of your collected wild plant with the available literature.

No one mentioned plant keys. Most areas will have a "bible" of all plant species that exist in that area, and a key (a series of branching, two option questions) that will eventually lead you to the species. At the very least you should be able to key out to the genus level, and then you can ask an expert for the final identification.

If you do a voucher, you'd better make sure to take a fruit and flower as well. Unless it's a common plant most can't be easily identified from the leaves alone.