Simple, accurate, and nondestructive methods of determining leaf area of pl
ants are important for many experimental comparisons, Determining individua
l leaf area (LA) of sunflower (Helianthus annuus L.) can involve measuring
leaf length (L) and breadth (B). The objectives of this held study were to
compare published and new models to determine the most precise model to pre
dict the area of individual leaves of sunflower plants and to test the appl
icability of these models between sowing times, with three genotypes differ
ing in maturity and stature; and at different times during crop growth. The
best model, which included both the L and B factors (LA = at. + dL + eLB c), accommodated changing leaf shape during crop development. The relation
ship between leaf dimensions and LA was significantly improved when sowing
time and the times of leaf sampling were included in the relationship; howe
ver, no significant differences were found among genotypes. The relative in
crease in precision with more complex models was considered. Both length an
d breadth measurements were needed to attain precision for all leaf sizes,
and given the availability of computer-based statistical packages, the use
of relatively complex models in the assessment of individual leaf areas wou
ld appear to be a practical option.