wall ruen. A small, delicate fern (Asplenium ruta-muraria) that grows on rocks or in rocky crevices.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.wall rue n (Plants) a delicate fern, Asplenium ruta-muraria, that grows in rocky crevices and walls in North America and Eurasia Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014wall? rue` n. a small fern, Aspleniumrutamuraria, family Polypodiaceae, having fan-shaped leaflets and growing on walls and cliffs. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.