Cordaiteans in cordaite-dominated permineralized peat from Pennsylvanian coals in Iowa have been reconstructed as mangroves using root anatomy, peat taphonomy, and geochemical data. Macrofloral, palynofloral, and conodont biostratigraphy indicate that these peats come from the latest Atokan Blackoak coal and earliest Desmoinesian Cliffland coal (mid-Moscovian), both in the Kalo Formation. Thus, their depositional setting can be used to evaluate the mangrove hypothesis. In Recent mires, thick mangrove peats have accumulated in tropical to subtropical carbonate systems; in contrast, thick tropical freshwater peats have accumulated in siliclastic systems. Kalo Formation coals, which we interpret as freshwater deposits, formed in siliciclastic depositional settings, similar to those of modern tropical freshwater peat, and to other Pennsylvanian coals in North America interpreted as freshwater deposits. In the late Atokan and earliest Desmoinesian (mid-Moscovian), cordaiteans and tree ferns predominated in the Western Interior and Illinois Basins; lycopsids and cordaiteans predominated in the Appalachian and Donets Basins. The scarcity of lycopsid-only mires in North America during the late Atokan-earliest Desmoinesian (mid-Moscovian) suggests drier climates than during the mid-to-late Desmoinesian (late Moscovian). Rather than indicating mangrove swamps, cordaite-dominated peat may indicate climates with a low-rain' season. Although most plants in cordaite-dominated peat probably grew in freshwater, coastal mires in climate zones with seasons of low-rain' may harbor mangrove taxa. The Changuinola Swamp of Panama, a modern peat-accumulating wetland that has a low-rain' season, is a possible analog of ancient cordaite-dominated mires. In Changuinola, most plants require freshwater; however mangroves. sustained by salt-water influx into the swamp, grow along the seaward edge and along blackwater creeks. The low-rain' season hypothesis has implications for understanding rainfall amount and continuity during Pennsylvanian cyclothem deposition. The floral succession in diverse cordaite coals, from cordaiteans to tree ferns to lycopsids, suggests increasingly wet climate during coal accumulation. The position of these coals immediately above the sequence boundary suggests humid climate during early glacial melting for these cyclothems. (C) 2009 Elsevier B.V. All rights reserved.