Phylotranscriptomics and genome size evolution in <i>Leucaena</i> (Fabaceae): Paleotetraploid genomic stability overshadows diploidization and environmental effects

The phylogenetic results illustrate the complex interplay of intrinsic and external factors that impact speciation, including ancient whole-genome duplication (WGD), cladogenesis, secondary contact, and allopolyploidy. A weak relationship between genome size and environmental variables suggests that other factors, including paleotetraploid genomic stability, have constrained genome size variation following a WGD 16+ million years ago. The findings are consistent with a small but growing number of studies identifying groups with ancient WGDs that resist diploidization associated with gene and DNA loss.