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A detailed description of grass seedling root morphology is essential to understand the differences in the establishment process among grasses. A repeated greenhouse study using a 1:1 mixture of Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) and coarse sand was conducted to determine root morphology differences at the third-leaf stage among nine cool-season forage grasses, creeping foxtail (Alopecurus arundinaceous Poir., reed canarygrass, (Phalaris arundinacea L.), smooth bromegrass (Bromus inermis Leyss.), tall fescue (Festuca arundinacea Schreb.), orchardgrass (Dactylis glomerata L.), russian wildrye (Elymus junceus Fish.), crested wheatgrass [Agropyron cristatum (L.) Gaertn.], intermediate wheatgrass [A. intermedian (Host) Beauv.], and western wheatgrass (A. smithii Rydb.); and nine warm-season forage grasses, sideoats grama [Bouteloua curtipendula (Michx.) Torr.], blue grama [B. gracilis (H.B.K.) Lag. ex. Steud.], sand lovegrass [Eragrostis trichodes (Nutt.) Wood], big bluestem (Andropogon gerardii var gerardii) Vitman, sand bluestem [Schizachyrium scoparium (Michx.) Nash], caucasian bluestem [Bothriochloa caucasica (Trin.) C.E. Hubb.], indiangrass [Sorghastrum nutans (L.) Nash], and switchgrass (Panicum virgatum L.). These grasses were selected as representative forage grasses of the northern USA. Andropogoneae species reached third leaf emergence 3 to 5 days earlier than other warm-season grasses and 3 to 15 days earlier than cool-season grasses. Most cool-season grasses had no or little subcoleoptile internode elongation except Aveneae species. Aveneae species and warm-season grasses, except Chlorideae species, had root development from the subcoleoptile internode. Sand bluestem had less subcoleoptile internode root development than big bluestem. Seminal root development was greater in species of the Triticeae tribe. Adventitous root development occurred by the three-leaf stage on species of all tribes except for Andropogoneae members. Most grasses were in a juvenile period of root growth at third leaf emergence. Stage of root development did not coincide with stage of shoot development among species.