Meswak at Nizamuddin Basti, Delhi

If you go to Nizamuddin during the month of Ramzan, you will always spot the meswak sellers doing brisk business:

Meswak / Miswak / Siwak, Nizamuddin, Delhi
Spotted on the Delhi Magic Heritage Walk through Nizamuddin: 
http://delhimagic.com/heritage-walk-nizamuddin.html

Meswak is a traditional way of cleaning teeth and is widely used among Muslims in India. It is sometimes spelt as miswak, and it's also called siwak. 

Sales of meswak shoot up during Ramzan, because during fasting, you are not allowed to brush your teeth with toothpaste (as the fast will be considered broken). Meswak is "sunnah" (approved way of life), so you can use it to clean your mouth. Meswak triggers the flow of saliva. Swallowing this saliva is considered ok (whereas there are usually restrictions on swallowing saliva during fasting). 

Cutting implements used to shape the Miswak and scrape off the bark..
If the twig is whitish, it means it is fresh and good for use

The meswak is a shrub / small tree. Its natural habitats in India are near mangroves, in saline lands, thorn shrubs, desert flood plains and along drainage lines in arid zones. It can tolerate lots of salinity.  

The scientific name is Salvadora Persica; this fancy name was bestowed upon the tree by Dr. Laurent Garcin (1683-1751), a French naturalist working with the East India Company. In choosing the name "Salvadora" Dr. Garcin was honouring a 17th century apothecary from Spain, Juan Salvador i Bosca (1598-1681). The "Persica" refers to Persia, where the "true specimen" of the tree is said to be from.

To me the Salvadora Persica looks very much like a tree which is native to India, because it is widespread and has names in several Indian languages, including Samskrit. Some examples below:

Hindi: मेस्वाक meswak, पिलु pilu 

Kannada: ಗೊನಿಮರ gonimara 

Marathi: khakan, पिलु pilu

Sanskrit: गुडफल gudaphala, पिलु pilu

Tamil: உகா uka

Telugu: గున్నంగి gunnangi

Here is a photo of the plant in its natural settings, from Salem Al Shekaili's flickr page. Looks like a very uninspiring and ordinary shrub, doesn't it? But it is a valuable resource - the leaves are used as food (they have a mustardy flavour), the bark has medicinal properties, and it is being widely planted in Kutch as part of reforestation attempts.

Salvadora Persica, by Salem Al Shekaili

In fact, to check to the versatile plants of the desert, you should head over to Salem Al Shekaili's really fabulous page to see his full collection of halophytes (plants which grow in saline environments).