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Selection at the seedling stage in grass breeding would be useful if seedling traits were correlated to desired agronomic traits of mature plants. Objectives of this study were to determine if seedlings from big bluestem (Andropogon gerardii Vitman) and switchgrass (Panicumvirgatum L.) populations that differ genetically in seedling tiller num- ber differ in mature plant (i) morphological characteristics, (ii) forage yield managed by a three-cut harvest system or a single end-of-season harvest, and (iii) leaf elongation rate. Field experiments were conducted on a Kennebec silt loam soil (fine-silty, mixed, superactive, mesic Cumulic Hapludolls). In addition, greenhouse studies were con-ducted in 1999 through 2001. Seedlings from big bluestem and switchgrass populations that differed for seedling tiller numbers were transplanted into spaced-planted field nurseries and greenhouse pots for study. Leaf width, leaf length, plant height, number of tillers per plant, yield, and leaf elongation rate were measured. Mature plant morphological characteristics differed between multiple-tiller and single-tiller plant types for both big bluestem and switchgrass. There were no differences in forage yield for big bluestem plant types. Switchgrass single-tiller plant types yielded 200 g plant-1 more than multiple- tiller types when harvested only once. Leaf elongation rate was 22 and 28% greater for single-tiller types vs. multiple-tiller types for big bluestem and switchgrass, respectively. Selection at the seedling level for tiller number appears to be an effective method to develop genotypes differing in yield per tiller, which has been shown to affect herbage yield when grown in swards.