Summary. A comparative study of the leaf outline morphometrics of Monstera adansonii var. klotzschiana, M. adansonii
var. laniata and M. praetermissa was carried out. The study focused on populations in isolated montane humid
(brejo) forests of Ceará state in Northeast Brazil and compared them with populations from Amazonia and the
Brazilian Atlantic Forest. Digitised outlines were prepared from a total of 1,695 field-collected leaf images from 20
populations, and elliptic Fourier analysis was used to generate matrices of coefficients, from which six shape
variables (principal components) were extracted using Principal Components Analysis. Intra-population variability
and inter-population differences were analysed with multivariate distance methods. Separate analyses were carried
out for each of three leaf size classes (juvenile, submature, mature) because of the strong heteroblasty typical of
this genus. Juvenile leaves were the least variable size class within populations of M. adansonii var. klotzschiana. The
shape variables expressed very similar types of variation in all three size classes. The Ceará brejo populations of M.
adansonii var. klotzschiana showed significant differences between mature leaf outlines in all pairwise comparisons;
the Pacatuba population was the most distinct. The Ceará populations did not cluster together exclusively. In all
three size classes, populations clustered together into their taxonomic groups, most clearly so in mature leaves. No
correlation between morphological and geographic distance matrices was found, nor between morphological and
molecular distance. The study showed that leaf outline shape is a practicable and useful quantitative trait for
studying morphological variability at species, varietal and population levels.