Medicinal plants as a group comprise approximately 8000 species and account for around 50% of all the higher flowering plant species of India. The largest number of medicinal plants are known to occur in dry deciduous forest as compared to the evergreen or temperate forests.

Macro analysis of the distribution of medicinal plants show that they are distributed across diverse habitats and landscapes across the country.  Around 70% of them are found in tropical areas mostly in the various forest types spread across the Western and Eastern Ghats, the Vindhyas, Chotta Nagpur plateau, Aravalis & Himalayas.  Although less than 30% of the medicinal plants are found in the temperate and alpine areas and higher altitudes they include species of high medicinal value. A smaller number is also seen in aquatic habitats and mangroves.

In order to have a broad picture of the medicinal plant diversity of the country, an attempt has been made to enlist them under different bio-geographic zone or region. The 'Trans Himalayan' bio-geographic zone is estimated to harbour approximately 700 known medicinal plant species.  Some of the well known ones, existing in the very cold and desert like conditions of this region are Ephedra gerardiana Wall., Hippophae rhamnoides L., Arnebia euchroma (Royle) John etc. The 'Himalayan' zone consists of North-West Himalayas, West Himalayas, Central Himalayas and East Himalayas biotic provinces. The North-West and West Himalayas region is estimated to have approximately 1,700 known medicinal plant species.  Some of the well-known species of these regions are Aconitum heterophyllum Wall. Ex Royle, Ferula jaeschkeana Vatkeand Saussurea costus (Balc.) Lipsd.  S. costus (syn. S. lappa C. B. Clarke) is in fact confined to only the Himalayan region of Jammu & Kashmir state and is cultivated elsewhere, including Lahaul district of Himachal Pradesh. This critically endangered variety, in the wild, is enlisted in Appendix I of CITES (Convention on International Trade in Endangered Species of flora and fauna).  The Central and Eastern Himalayan biotic provinces, put together, are estimated to harbour around 1,200 known medicinal plant species.  A few of the well known ones are Nardostachys grandiflora DC., Taxus wallichiana Zucc., Rhododendron anthopogon D.Don and Panax pseudoginseng Wall.  While Panax pseudoginseng is seen only in the Eastern Himalayas, Nardostachys grandiflora DC and Taxus wallichiana Zucc have already been included in Appendix II of CITES.

Despite the fact that the 'Desert' bio-geographic zone consisting of Kutch and Thar biotic provinces support only sparse vegetation, it is a haven for almost 500 known medicinal plant species.  Some of the well-known ones of this region are Convolvulus microphyllus Seib ex Spreng (Syn C. pluricaulis Chois), Tecomella undulata (Sm.)Seem, Citrullus colocynthis (L.) Schraderand Cressa cretica L.

The 'Semi-Arid' zone consists of biotic provinces of Punjab and Gujarat - Rajwar and is estimated to be a home for around 1,000 known medicinal plant species. Commiphora wightii (A.) Bhandari, Caesalpinia bonduc (L.) Roxb., Balanites aegyptiaca (L.) Delile and Tribulus rajasthanensis Bhandari & Sharma are some of them. Tribulus rajasthanensis is almost endemic to this region in India while extending into adjoining areas of Pakistan.

Known for its rich bio-diversity, the "Western Ghats" bio-geographic zone consisting of Malabar coast and Western Ghats is one of the eighteen hot spots of bio-diversity recognized across the globe. Approximately 2000 known medicinal plant species, many of these are endemic to this region, are seen here.  Among its endemic species are Myristica malabarica Lam., Garcinia indica (Dup.) Choisy, Utleria salicifolia Bedd.and Vateria indica L. These species have been assessed to be under varying degree of threat of extinction ranging from Vulnerable (VU) in case of Vateria indica L. to Critically Endangered (CR) Utleria salicifolia Bedd.

The 'Deccan Peninsula' covers the largest chunk of land mass amongst all the ten bio-geographic zones consists of five biotic provinces - Deccan Plateau South, Central Plateau, Eastern Plateau, Chhota Nagpur and Central Highlands.  This zone has the highest proportion of India's entire medicinal plant diversity and the total number of known species is estimated to be around 3000.  The well known endemic species of this region are Pterocarpus santalinus L.f., Decalepis hamiltonii Wight & Arn., Terminalia pallida Brandisand Shorea tumbuggaia Roxb of which Pterocarpus santalinus L.f is already included in Appendix II of CITES.

The 'Gangetic Plain' consisting of Upper Gangetic Plain and Lower Gangetic Plain biotic provinces is estimated to have around 1000 known medicinal plant species. A few of the well known ones of this region are Holarrhena pubescens (Buch-Ham.) Wallich ex DC., Mallotus philippensis (Lam.) Muell.-Arg., Pluchea lanceolata C. B.Clarkeand Peganum harmala L.

The 'North-East India' with an estimated 2000 medicinal plant species population is yet another high bio-diversity region of the country. Like the Western Ghats, this zone is also one of the eighteen hot spots with high levels of endemism.  It consists of two biotic provinces namely Brahmaputra Valley and Assam Hills. Aquilaria malaccensis Lam., Smilax glabra Roxb., Ambroma augusta  (L.) L.f. and Hydnocarpus kurzii (King) Warb are some of the well-known medicinal plants found here. Out of these, A. malaccensis Lam., is already included in Appendix II of CITES.

Andaman, Nicobar and Lakshadweep Islands form the 'Island' bio-geographic zone. Calophyllum inophyllum L., Adenanthera pavonina L., Barringtonia asiatica (L.) Kurzand Aisandra butyracea (Roxb.) Baehni are some of the important medicinal plants of this zone which is estimated to have around 1000 species.

The 'Coasts' bio-geographic zone comprising West Coast and East Coast is estimated to harbour around 500 plant species of known medicinal value.  A few of the well known ones amongst these are Rhizophora mucronata Lam., Acanthus ilicifolius L., Avicennia marina Vierh and Sonneratia caseolaris  (L.) Engl.

Studies show that a large percentage of the known medicinal plants occur in the dry and moist deciduous vegetation as compared to the evergreen or temperate habitats.  This is perhaps due to more intensive human (anthropological) interaction with plants in the deciduous tracts as compared to evergreen forests and also there is a greater degree of speciation in tropical forests as compared to the temperate vegetation.

Life forms:

Majority of the medicinal plant are higher flowering plants. Of the known plants of medicinal value little more than one third are trees and an equal portion shrubs and climbers. While herbs constitutes around one third of the total population, medicinal species are also found in lower plants like algae, fungi, lichens, bryophytes, pteridophytes, gymnosperms and angiosperms.

Families:

Of the 386 families and 2200 genera recorded, the families Asteraceae, Euphorbiaceae, Lamiaceae, Fabaceae, Rubiaceae, Poaceae, Acanthaceae, Rosaceae and Apiaceae share the larger proportion of medicinal plant species, with the highest number of species (419) falling under Asteraceae.