Genetic and morphological differentiation within Euphorbia japygica (Euphorbiaceae) suggests divergence of populations from the south-eastern Apennine Peninsula.

This article focuses on the phylogeographic patterns and taxonomic relationships within the Euphorbia nicaeensis species complex in the Apennine Peninsula and adjacent regions, specifically examining Euphorbia adriatica and Euphorbia japygica. Using an integrative approach that includes nuclear ITS sequencing, amplified fragment length polymorphisms (AFLP), relative genome size (RGS) estimation, chromosome counting, and morphometric analyses, the study finds weak genetic differentiation between these taxa that only partially corresponds to morphological differences, such as fruit indumentum. The data support recognizing a single species, Euphorbia japygica, with two subspecies: E. japygica subsp. japygica in southern Italy (Puglia and Basilicata) and E. japygica subsp. prostrata (formerly E. adriatica) distributed more broadly across the Apennines, southern Alps, and north-western Balkan Peninsula. The study highlights the phylogeographic distinctiveness of southern Italian populations and calls for further in-depth investigations into the diversification of Italian flora.