Short rotation biomass production for energy has become increasingly important. Of all the tree species in European temperate climate zone poplars are really the most promising species for biomass production because the are distinguished by fast growth and very simple, vegetative propagation. In the scope of a wider selection program, Poplar Research Institute tends to create new fast growing cultivars of poplars which can be used in plantations for biomass production. In this sense, one of the main objectives is the speeding up of selection procedure, i.e. the shortening of the period between the creation of the clone and beginning of production. In this aim, various anatomical and physiological characteristics of plant organs are researched, i.e. their structural-physiological relations, so as to recognize the fast growing genotypes. The paper deals with the results of the investigation of net photosynthesis, leaf area, stomata number, as well as diameter, height, and biomass production of rooted cuttings of poplar clones (Populus nigra L., Populus x euramericana (Dode) Guinier, and Populus deltoides Bartr). The obtained results show that there was high interclonal variability and statistically highly significant differences between the parameters under consideration. The highest values of rate of photosynthesis, stomata number, leaf area, diameter, and height, as well as biomass, on the average, were obtained with clones of eastern cottonwood (P. deltoides), then euramerican poplar (P. x euramericana), whereas the smallest in common black poplar (P. nigra). Also, high correlation coefficients between rate of photosynthesis and biomass production, number of stomata on adaxial epidermis and biomass production, as well as leaf area and biomass, pointing to the possibility of employment of these parameters in early selection for luxuriant growth and biomass production were obtained. The results of hierarchical cluster analysis (Euclidean distance) point to a high tendency of grouping of clones according to species to which they belong. A considerable variability between investigated clones within species was observed. Therefore, a possibility of employment of certain parameters in the individual selection genotypes, as well as in choosing parent pairs in breeding by hybridization is present.