  In this study, we investigate the problem of comparing gene trees reconciled
with the same species tree using a novel semi-metric, called the Path-Label
Reconciliation (PLR) dissimilarity measure. This approach not only quantifies
differences in the topology of reconciled gene trees, but also considers
discrepancies in predicted ancestral gene-species maps and
speciation/duplication events, offering a refinement of existing metrics such
as Robinson-Foulds (RF) and their labeled extensions LRF and ELRF. A tunable
parameter {\alpha} also allows users to adjust the balance between its species
map and event labeling components. We show that PLR can be computed in linear
time and that it is a semi-metric. We also discuss the diameters of reconciled
gene tree measures, which are important in practice for normalization, and
provide initial bounds on PLR, LRF, and ELRF. To validate PLR, we simulate
reconciliations and perform comparisons with LRF and ELRF. The results show
that PLR provides a more evenly distributed range of distances, making it less
susceptible to overestimating differences in the presence of small topological
changes, while at the same time being computationally efficient. Our findings
suggest that the theoretical diameter is rarely reached in practice. The PLR
measure advances phylogenetic reconciliation by combining theoretical rigor
with practical applicability. Future research will refine its mathematical
properties, explore its performance on different tree types, and integrate it
with existing bioinformatics tools for large-scale evolutionary analyses. The
open source code is available at: https://pypi.org/project/parle/.
