Arundo donax L. displays unique physiological features whereby it readily absorbs and concentrates toxic chemicals from contaminated soil with no appreciable harm to its own growth and development. However, the potentially invasive reputation of the plant led to its rejection for phytoremediation or plantation largely out of fear of its spread. It is a clonal species believed to spread predominantly asexually by dispersal of fragments as viable seeds or seedlings have never been found and genetic fingerprinting indicated a single genetic clone in the U.S.. The investigation reported here clearly shows that A. donax does not produce pollen or viable seeds. Microspores could be seen with very low frequency, but microgametogenesis to produce the tube and generative nucleus was not observed. Approximately 10% of the ovaries enlarge and take on the character of mature caryopses. All structural features of ovaries and anthers were examined in clearing fluid by median optical sagittal sectioning utilizing a Raj slide modified for this purpose. The single anatropous bitegmic ovule within the enlarged caryopsis contains a massive crassinucellate nucellus with cells of uniform size. The occasional archesporial cell fails to produce a megasporocyte. Enlarged caryopses placed in several standard germination environments failed to produce new plants thus to assure that enlarged ovules do not function as vegetative propagules and the structure is in fact a pseudocaryopsis. The spread of A. donax beyond the margins of the plots could occur only by rhizomatous growth and fragments, which by the application of simple precautions could be impeded. (c) 2012 Elsevier Ltd. All rights