Thousands of species grow well in the different climatic zones of India but some species do not take kindly to root cutting and pruning. Yet others have peculiar growth habits that make it difficult to create convincing bonsai.Plants with the greatest potential are those with naturally small leaves, fruits and flowers, for these look automatically in scale in small bonsai pots.

Its best to start with trees that commonly grow in the area and climate you live in. Such trees need less effort to keep healthy and are forgiving of intensive training. Moreover their full grown kin around can act as models and sources of inspiration.

Most tropical trees that are hardy in more humid coastal areas can be classed as trees of medium difficulty in Delhi. They need protection in the hot dry summers and during the coldest part of winter.
Trees hardy in the mountains also require summer protection. We are fortunate to have cold winters that help some of these to survive.

In general with a rare tree let it survive in a large flower pot till its health convinces you it's ready for bonsai.

The king of flowering trees is the Bougainvillea in all its varieties and colours. It is hardy and can survive most mistakes. Repot in the monsoons and if wire is felt necessary, use it only on green branches as the wood is very brittle.Full sun keeps the growth compact and watering should be restricted, especially when its flowering.It should be pruned drastically after flowering. In the young state pruning for taper and ramifications is necessary even if it means losing the flower buds.
Lantana is another interesting tree that flowers easily. Its branches are extremely brittle so wire should never be used. Calliandra with its powder-puff flowers and strawberry buds is very attractive. The short-lived flowers should be removed as soon as they wither. Malphigia Coccigera has small crinkled flowers with a delicate smell. Lagerstroemia indica flowers in the monsoons and comes in three interesting colours.
Other flowering trees that may be tried are Murraya, Carmona, Braaya, Carissa or jangli karaunda, and gardenia.

In Delhi, and in general in the northern plains, the following trees are usually hardy for Bonsai:

Ficus varieties

Ficus virens, religiosa (which also has a cousin called the paras pipal that reduces its leaf size quite dramatically), benjamina, retusa, nuda, nitida, benghalensis (though it doesn't show quick reduction in leaf size), panda, longisland etc.

Morus or mulberry

There is a wild variety with attractive indented leaf margins and a trunk that is almost orange.

Acacia varieties

Subabul, kikar, jhand etc.Compound leaves,some with thorns.Suitable for groups.

Others

Diospyros montana or basendu and the Pithocellobium dulce or jangal jalebi.

Here's a list of fifty trees suitable for bonsai in the plains of North India for you to print out.Be aware that not all are hardy.

Casurina

Top growth must be kept under strict check. Has a tendency to lose branches suddenly.

Celtis australis

Difficult to find. Also puts out spindly branches which need tackling at the right time.

Ficus varieties

Ficus carica, the edible fig, and Ficus glomorata or gular which prefer slightly cooler climes. Ficus Tseila has a tendency to lose branches suddenly.

Some shrubs

Duranta, Calliandra and Malphigia that need careful repotting and pruning.

Juniperus prostrata

Very slow growing.Needs protection from the hottest summer sun and careful repotting with minimum root disturbance.

The choice of fruiting trees is limited because of the size of most fruits and also because trees do not fruit happily in pots. However there are two popular choices in the Citrus japonica or China orange and the punica granatum nana or miniature pomegranate. Fruiting requires a large and exhausting effort from the tree so it is advisable to remove some of the fruit if it is too profuse.
Hardy Ficus varieties are also fruiting trees as many of them bear bright red figs, as is the mulberry, which can look extremely elegant with its fresh green spring fruit.