Flora of the Southeastern United States
2022 Edition

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Key to Taxodium

1 Plant essentially evergreen; branches of male cones long and slender, open, composed of single cones or tight cluster of several cones; plant without knees; [s. TX]
1 Plant deciduous; branches with male cones short and crowded, the cones commonly in short compact secondary branches; plant with knees; [c. TX eastwards].
..2 Larger knees short, rarely > 4 dm tall, usually columnar or broad and mound-like, with thick, compact bark on top; leafy branchlets ascending from the twigs, secundly erect (the base often curving, the apical portion of the branchlet borne in a vertical plane), except on juvenile trees (which mimic T. distichum); leaves subulate, spirally arranged, not spreading laterally and featherlike (except on juvenile trees), ascending or appressed; leaves mostly 3-10 mm long (to 15 mm long on juvenile trees); bark thick (1-2.5 cm thick), furrowed, dark-brown, not exfoliating; [trees mainly of fire-maintained habitats: isolated depressions (clay-based Carolina bays, depression ponds), wet pine savannas, pocosins and other wet peaty habitats, domes and stringers in wet prairies, and, less commonly, blackwater swamps and natural lakes]
..2 Larger knees often tall, often > 4 dm tall, usually narrowly conical, with thin, shreddy bark on top; leafy branchlets spreading laterally from the twigs, except in the crowns of mature trees (which sometimes mimic T. ascendens); leaves linear, flat, spirally arranged but by twisting of their basal portions spreading laterally and featherlike (pseudo-distichous), appressed only on drooping branches of the crown, if at all; leaves mostly 8-20 mm long (sometimes less on crown branches); bark thin (< 1 cm thick), exfoliating in shreddy, orange-brown strips; [trees of brownwater swamp forests, blackwater swamp forests, natural lakes, and millponds]