1 Introduction
The tribal people of Khammam district of Andhra Pradesh are still practicing herbal remedies for the treatment of their common diseases and disorders. Khammam district lies between 16⁰ 45’ and 18⁰ 35’ N latitude and 79⁰ 47’ to 81⁰ 47’ E longitude occupying a forest area of 7, 594.38 sq km. The largest river of South India, the Godavari passes through this district. The Khammam district has the highest tribal population (26.47% as per 2011 census) in the state with six tribal communities, viz., Koya, Lambad, Gond/Naikpod, Yerukula, Nayak and Konda Reddi. 

2 Material and Methods
Ethnobotanical survey was conducted once in every two months from 2008 to 2012 in a duration of 10-15 days. About 4-7 days were spent during each field trip with different tribal communities at their dwellings. After establishing good rapport with them, the utility of plants and detailed methods of uses were documented. The plant species collected were identified with the help of International Code of Botanical Nomenclature and also by referring them to the herbarium collections maintained in the department of Botany, Andhra University, Visakhapatnam (Gamble and Fisher, 1957). The voucher specimens of the present study were also deposited there.

3 Enumeration
The plants are enumerated and presented in a tabular form with Vernacular name, followed by Latin name, Voucher No., Ethnomedicinal uses, Parts used, and Method of preparation. Plants and practices marked with an asterisk (*) are considered to be new or less known.

4 Results and discussion
The present study yielded 77 species of plants covering 68 genera and 37 families used for common skin diseases by the tribals of Khammam district of Andhra Pradesh. Caesalpiniaceae is the dominant (9 sps) family followed by Fabaceae (6 sps), Euphorbiaceae (5 sp), Zingiberaceae (4 sps), Mimosaceae, Poaceae, Asteraceae, Lamiaceae (with 3sps each), Cucurbitaceae, Verbenaceae, Annonaceaee, Rutaceae, Myrtaceae, Boraginaceae, Tiliaceae, Apocynaceae, Combretaceae (2 sps each) and the rest of the families with one species each. Habit-wise analysis showed the dominance of herbs (33) followed by trees (29), shrubs (12) and climbers (3). Morphological analysis showed maximum utilization of leaf in 37 practices followed by whole plant (11), fruit, seed (7 each), stem bark, root (6 each), flower (4), rhizome, stem (3 each) and tuber (1).They are used either in the form of paste, powder, juice, decoction or ash and applied either with water, castor oil, coconut oil, cheese, turmeric powder, salt, or pepper powder. Caesalpinia sappan, Caralluma umbellata, Clerodendrum paniculatum, Grewia flavescens, Leucas aspera, Merremia aegyptia and 41 practices were found to be new (Jain, 1991; Kirtikar and Basu, 2003).

Acalypha indica, Aegle marmelos, Annona squamosa, Cynodon dactylon, Lawsonia inermis, Leucas aspera, Limonia acidissima, Moringa oleifera, Psidium guajava, Tamarindus indica  are also used against skin diseases in Bargarh district of Orissa (Sen and Behera, 2003). Cassia fistula, Lantana camara, Luffa acutangula, Piper nigrum, Pongamia pinnata, Tagetes erecta are also used for curing various skin ailments by the tribals in different parts of India (Kirn et al., 2003). Aegle marmelos, Anacardium occidentale, Curcuma aromatica, Cynodon dactylon, Euphorbia hirta, Lawsonia inermis, Madhuca indica, Pongamia pinnata are also used against skin diseases in traditional treatment of skin diseases in South Travancore, southern peninsular India (Jeeva et al., 2007). Anacardium occidentale, Cardiospermum halicacabum, Cassia fistula, Jatropha curcas, Lawsonia inermis, Myristica fragrans, Phyllanthus amarus, Piper nigrum, Syzygium cumini, Terminalia chebula and Vernonia cinerea are also used for curing a variety of skin diseases by the tribas of Wayanad district of Kerala (Nisha and Sivadasan, 2007). Cassia fistula, Lantana camara, Lawsonia inermis, Tamarindus indica are also used for curing various skin diseases by the rural folk of Bidar district, Karnataka (Prashantkumar and Vidyasagar, 2008). Aegle marmelos, Anacardium occidentale, Curcuma aromatica, Cynodon dactylon, Euphorbia hirta, Lawsonia inermis, Madhuca indica, Pongamia pinnata are also used for treating skin diseases in Kanyakumari district of Tamil Nadu (Kingston et al., 2009). Acalypha indica, Cassia tora, Cynodon dactylon, Lawsonia inermis, Leucas aspera, Madhuca indica, Pongamia pinnata, Sphaeranthus indicus, Vernonia cinerea are also used for curing skin diseases in Karnataka (Shiddamallayya et al., 2010). Aegle marmelos, Anacardium occidentale, Cassia fistula, Lawsonia inermis, Phyllanthus amarus, Piper nigrum and Tabernaemontana divaricata are also used for curing a variety of skin diseases by the people of Thiruvananthapuram district of Kerala (Arya et al., 2015).The same plant may not be used for curing the same skin disease in different parts of India but it may be used to cure some other skin ailment. Sometimes even if it is used for the same disease the plant part may be varying. The present study represents a contribution to the existing knowledge of folk remedies that are in current practice for treatment of skin diseases, which happens to be the most common ailment amongst tribal population because of their unhygienic living conditions. Once the efficacy of these herbal drugs in treating skin diseases is scientifically established, the popularization of these remedies can be recommended in Indian healthcare system for wider application, since these plants are well within the reach of the tribal masses.

5 Conclusions
There is a need for scientific validation of these practices and their efficiency, credibility and applicability need to be established through phytochemical, pharmacological and clinical screenings. Thus, the information presented here provides an opportunity to study their active secondary metabolites in terms of searching new herbal drugs for preparing better remedies for skin diseases in future.

Acknowledgement
The authors are grateful to the tribals of Khammam district for their help in field work and sharing their valuable knowledge on common skin diseases.

References
Arya S., Adarsh G., Anand S.K., Kumar N.S., and Santoshkumar R., 2015, Selected medicinally and economically important plants growing in Aruvippuram area of Thiruvananthapuram district, Kerala, India, Journal of Tropical Medicinal Plants, 15: 19-31

Jain S.K., 1991, Dictionary of Indian Folk Medicine and Ethnobotany, Deep Publications, New Delhi

Jeeva G.M., Jeeva S., and  Kingston C., 2007, Traditional treatment of skin diseases in South Travancore, southern peninsular India, Indian Journal of  Traditional Knowledge, 6: 498-501

Kingston C., Jeeva S., Jeeva G.M., Kiruba S., Mishra B.P., and Kannan D., 2009, Indigenous knowledge of using medicinal plants in treating skin diseases in Kanyakumari district, Southern India, Indian Journal of  Traditional Knowledge, 8: 196-200

Kirn H.S., Kapahi B.K., and Baleshwar, 2003, Ethnobotanic medical treatment of skin diseases in India, Journal of  Non-Timber Forest Products, 10: 172-181

Kirtikar K.R., and Basu B.D., 2003 (Reprinted), Indian Medicinal Plants, Oriental Enterprises, Dehra Dun, Uttaranchal

Nisha V.M., and Sivadasan M., 2007, Ethnodermatologically significant plants used by traditional healers of Wayanad district, Kerala, Ethnobotany, 19: 55-61

Prashantkumar P., and Vidyasagar G.M., 2008, Traditional knowledge on medicinal plants used for the treatment of skin diseases in Bidar district, Karnataka,  Indian Journal of Traditional Knowledge, 7: 273-276

Sen S.K., and Behera L.M., 2003, Ethnomedicinal plants used against skin diseases in Bargarh district in Orissa, Ethnobotany, 15: 90-96

Shiddamallayya N., Yasmeen A., and Gopakumar K., 2010, Hundred common forest medicinal plants of Karnataka in primary healthcare, Indian Journal of Traditional Knowledge, 9: 90-95