Seed surface ultrastructure as an efficient tool for species delimitation in the Allium ampeloprasum L. alliance (Amaryllidaceae, Allioideae).

Seed surface ultrastructure shows a wide variation among different species of the genus Allium that could potentially provide valuable characters in inferring the relationships. In order to evaluate inter- and intraspecific variation of testa microsculpturing in the leek alliance, 33 seed samples of Allium representing its two subgenera, six sections, and 23 species were studied. Seed testa surface was analyzed using both SEM and Stereomicroscopy. Minor differences in testa cell arrangement were observed between members of sect. Allium and sect. Avulsea (both of subg. Allium), but major contrasts were discerned between them and members of subg. Cepa. Significant similarity was distinguished in anticlinal walls of the members of sect. Allium and sect. Avulsea: they were variously undulated (U-, to ±Ω-like). Testa cells in members of subg. Cepa, and some of subg. Allium (sect. Caerulea, sect. Codonoprasum, and sect. Longivaginata) showed ribbed anticlinal walls suggesting a close relationship between them. The periclinal walls were concave, flat to convex with testa cells densely granulose at margins in sect. Caerulea; flat to convex, irregularly granulose-verrucose in sect. Codonoprasum; concave, densely granulose at margins and center in sect. Longivaginata; and convex, densely irregularly granulose, sometimes centrally verrucose in subg. Cepa. Irregularly polygonal cells were present in most species, but elongated polygonal cells in two species, A. iranicum and A. wendelboi (sect. Allium). We found significant micromorphological similarity in seed surface features between A. abbasii and A. fuscoviolaceum; A. esfandiarii and A. atroviolaceum; and A. longipapillatum and A. rotundum, corroborating close relationships.