AMERICAN MISTLETOE (PHORADENDRON LEUCARPUM SSP. LEUCARPUM, VISCACEAE) OCCURRENCE IN HOST TREES WITHIN THE CITY OF CAIRO, ALEXANDER COUNTY, ILLINOIS, AND ITS INCIDENCE IN ILLINOIS, U.S.A

A comprehensive survey of American mistletoe [Phoradendron leucarpum (Raf.) Reveal & M.C. Johnston ssp. leucarpum, Viscaceae] occurrence in host trees was conducted within the incorporated city limits of Cairo, Illinois, from 2011–2013. An extensive herbaria search for Illinois mistletoe specimens was completed in 2012, and a mistletoe reconnaissance was also made in 2013 to verify its present occurrence within 14 southern Illinois counties. Cairo, a historic river city and the county seat of Alexander County, is the southernmost city in Illinois, near the confluence of the Ohio and Mississippi Rivers. In Cairo, Phoradendron leucarpum ssp. leucarpum was observed in 547 host trees among 13 tree species (9 native, 4 introduced exotics). The two predominate host trees documented were Acer saccharinum (304 trees) and Ulmus americana (111 trees). The mistletoe occurrence value of Cairo is 13.41 host trees per km, the highest incidence of American mistletoe and greatest number of host species for a city of its size in Illinois. A statewide assessment of 19 southern Illinois counties resulted in 225 mistletoe specimens examined: 52 specimens collected in Cairo, 97 annotated from herbarium searches, and 76 additional specimens collected during the 14 county mistletoe host tree survey. Twenty-one host tree species were documented among those herbarium specimens. The top three host tree species by Illinois counties were Ulmus americana (16), Acer saccharinum (8), and Nyssa sylvatica (8). New North American mistletoe host trees documented were Acer palmatum, Betula utilis ssp. jacquemontii, and Styphnolobium japonicum. Duration of low winter temperatures has been the determining factor in the northern extension of mistletoe in southern Illinois over time. Un estudio exhaustivo de la ocurrencia de muérdago americano [Phoradendron leucarpum (Raf.) Reveal & MC Johnston ssp. leucarpum, Viscaceae] en los árboles hospedadores se llevó a cabo dentro de los límites incorporados de la ciudad de Cairo, Illinois, entre 2011-2013. Se completó una extensa búsqueda para especímenes de herbario de muérdago de Illinois en 2012, y también se hizo un reconocimiento secundario de muérdago en 2013 para verificar su ocurrencia actual en 14 condados del sur de Illinois. Cairo, una ciudad ribereña histórica vieja y el asiento del Condado de Alexander, es la ciudad más meridional de Illinois, cerca de la confluencia de los ríos Ohio y Mississippi. Phoradendron leucarpum ssp. leucarpum se ob