An extensive colony of Asplenium heterochroum was found growing on the 125 year old walls of the Yulee Sugar Mill, Yulee Sugar Mill State Historic Site, Homosassa, Citrus County, Florida. The extremely local and generally rare species normally grows on limestone rocks in woods or grottos and has never been recorded on man-made structures. It was found to be hexaploid (108 pairs at meiotic metaphase) and possessed fronds up to 37 cm in length (twice the stature of previously recorded North America collections).