The present study on fossil plants comprising well-preserved leaf and fruit impressions from the Siwalik sediments exposed near Koilabas in western Nepal is the first detailed and systematic work. The floral assemblage recovered from these sediments is impoverished both in quality and quantity as constituted by 25 species belonging to 22 genera and 15 dicotyledonous families of angiosperms. This assemblage adds significant data to the Siwalik Palaeobotany. On the basis of present assemblage as well as already known data from the area, the palaeoclimate, palaeoecology, and phytogeography of the area during the Mio-Pliocene in the Himalayan foothills have been deduced. The significance of the physiognomic characters of the fossil leaves in relation to climate has also been discussed.

In the present paper some more angiospermous leaf-impressions recovered from Ghish River, Lish River and Sevok Road section in Darjeeling District, West Bengal have been described, These are-Flacourtia tertiara Prasad & Awasthi 1996, Alsodeia palaeoracemosa sp. nov. (Flacourtiaceae), Shorea bengalensis sp. nov. (Dipterocarpaceae), Zizyphus palaeoapetala sp. nov., Ventilago tistaensis sp. nov. (Rhamnaceae), Syzygium palaeocuminii Prasad & Awasthi 1996 (Myrtaceae) and Homonoia mioriparia sp. nov. (Euphorbiaceae). Out of these seven taxa, five are new records to the Siwalik flora. The dominance of evergreen and moist deciduous elements in the assemblage further confirms the prevalence of warm and humid climate during the deposition of the Himalayan foreland sediments.

The fossil leaves belonging to the extant genera Dipterocarpus Gaertn. and Shorea Roxb. of the family Dipterocarpaceae have been described from the Middle Siwalik sediments exposed in Ghish River near Oodlabari in Darjeeling district, West Bengal. The occurrence of both these genera in the Siwalik sediments is phytogeographically significant and suggests the prevalence of warm humid climate during the deposition of Siwalik sediments in this region.

In the present paper five well-preserved leaf-impressions collected from the Siwalik sediments of Sevok Road cutting and Ramthi River sections in Darjeeling District, West Bengal have been described. These are Xanthophyllum mioflavescens sp. nov., Pterospermum siwalicum sp. nov., Swintonia miocenica Awasthi & Prasad, Millettia oodlabariensis sp. nov., and Glochidion (=Phyllanthus) palaeohirsutum sp. nov. showing close resemblance with the extant taxa Xanthophyllum flavescens Roxb., Pterospermum semi-sagittatum Ham., Swintonia floribunda Griff., Millettia albiflora Prain and Glochidiom birsutum Muell., of the families Xanthophyllaceae, Sterculiaceae, Anacardiaceae, Fabaceae and Euphorbiaceae, respectively. The presence of these elements in the Siwalik sediments further suggests the prevalence of tropical humid climate in the region during sedimentation.

A floral assemblage consisting of leaf-impressions recovered from the Lower Siwalik sediments of Seria Naka, about 30 km north-west of Tulsipur town in Gonda District of Uttar Pradesh, India has been described and discussed in the present paper. The assemblage comprises 10 taxa belonging to seven dicotyledonous families - Anonaceae, Flacourtiaceae, Polygalaceae, Sapindaceae, Anacardiaceae, Fabaceae and Ebenaceae. An analysis of the floral assemblage with respect to the distribution pattern of modem equivalent taxa reveals the prevalence of warm and humid climates in the region during the deposition of these sediments. The fossil flora also indicates that tropical evergreen forests with few moist deciduous plants were flourishing around Seria Naka in the Himalayan foot-hills during Middle Miocene in contrast to the mixed deciduous type of present-day forests. Further, the presence of some Malayan elements like Goniothalamus meboldii, Mitrephora macrophylla and Nephelium glabrum is phytogeographically important supporting the view of the migration of some taxa from Southeast Asia to the Indian subcontinent during the Neogene.