1 23 The Environmentalist ISSN 0251-1088 Volume 31 Number 3 Environmentalist (2011) 31:288-298 DOI 10.1007/s10669-011-9333-x Morphological and anatomical effects of crude oil on Pistia stratiotes Akintunde Abdul-Rasaq Akapo, S. O. Omidiji & A. A. Otitoloju