26 Parthenium hysterophorus and Bidens pilosa, two new records to the invasive weed flora of the United Arab Emirates Tamer Mahmoud 1* , Sanjay Gairola 1 , Ali El-Keblawy 2 1 Sharjah Seed Bank and Herbarium, Sharjah Research Academy, Sharjah, UAE 2 Dept of Applied Biology, Faculty of Science and Sharjah Research Academy, University of Sharjah, Sharjah, UAE *Corresponding author: tamer_mahmed@yahoo.com | Received: 26 January 2015 | Accepted: 19 February 2015 | ABSTRACT Parthenium hysterophorus L. and Bidens pilosa L., two species of Asteraceae, are recently recorded for the first time in the United Arab Emirates (UAE). This information is based on our recent field work and critical evaluation of the existing literature. P. hysterophorus is a highly invasive alien weed of global significance and is now present in more than 30 countries of its invasive range alone. In many parts of the world this weed has been reported to reduce the crop and pasture production, native plant biodiversity and human and animal health. The presence of these cosmopolitans under the hyperarid climates of UAE indicates their great tolerances to the harsh climatic conditions. Both species are considered as good colonizers; they have explosive reproductive potential and ability to thrive in diverse habitats. The population dynamics of the P. hysterophorus L. and B. pilosa L. should be monitored in order to assess their future spread. All known populations of these two invasive weeds need to be eradicated and cleared sites needs to be continuously monitored for the presence any soil seed bank. Plant specimens of P. hysterophorus and B. pilosa are deposited to the Sharjah Seed Bank and Herbarium (SSBH), UAE. Descriptions and photographs of these species are provided. Key Words: Parthenium hysterophorus, Bidens pilosa, Invasive weeds, Asteraceae, UAE, New record. INTRODUCTION Asteraceae is the largest family of flowering plants, with over 1600 genera and 23,000 species (Jeffrey, 2007). In the United Arab Emirates (UAE), it is represented by 36 genera and 59 species (Jongbloed, 2003; Karim and Fawzy, 2007; El- Keblawy et al., 2005). During the floristic studies (2013-2014) in Sharjah and Ras Al Khaimah of UAE (Fig. 1), the authors collected two invasive weed species, Parthenium hysterophorus and Bidens pilosa belonging to family Asteraceae. The comparisons of the morphological characteristics with similar species in the UAE and floras, mainly Saudi Arabia, Egypt, India, Pakistan, Australia, indicated that these species are new records for the flora of the UAE. Dr Samia Heneidak, a key taxonomist in the regional flora of the Middle East, also confirmed the identification of the two species as P. hysterophorus L. and B. pilosa L. The review of literature further confirmed that these two Journal on New Biological Reports JNBR 4(1) 26 – 32 (2015) ISSN 2319 – 1104 (Online) Published by www.researchtrend.net