Seed macro- and micromorphology in Allium (Amaryllidaceae) and its phylogenetic significance

Macro- and micromorphology of seeds are diagnostic characteristics of importance in delimiting taxa in Allium (Amaryllidaceae). However, there is no consensus on the phylogenetic significance of testa cell characteristics and whether they reflect the different evolutionary levels recognized in Allium.

Seeds of 95 species (98 samples) representing 14 subgenera and 58 sections of Allium were examined using scanning electron microscopy (SEM) for such traits as periclinal wall surface area of ten testa cells, distance between testa cells (macromorphology), testa cell shapes, and arrangement and structure of anticlinal and periclinal walls (micromorphology). The data matrix was subjected to cladistic analysis. The produced phylogenetic tree was examined against the molecular tree obtained from publically available ITS sequences.

The periclinal wall surface area of ten testa cells and the distance between them, examined for the first time, were found useful for delimitation of species in Allium. Based on seed macro- and micromorphology, we present a taxonomic key and a hypothetical reconstruction of the migration routes during the early stages of evolution of Allium.

The ancestors of Allium originated in an area bounded by the Caucasus, Central Asia and Iran. The seed testa morphology-based evolutionary state of a species is determined by two parameters: the shape of the periclinal walls and curvature of the anticlinal walls.