Seed morphology and its systematic implication in Noccaea s.l. (Brassicaceae)

The current research work was aimed to determine the macro- and micromorphological characters of seeds in Noccaea s.l. members and evaluate the potential phylogenetic utility of the seed coat character. Forty-two of the ca. 136 Noccaea s.l. species and one species of Thlaspi from 57 different accessions were investigated using light microscopy (LM) and scanning electron microscopy. Phylogenetic analysis was conducted by using internal transcribed spacer (ITS) DNA sequences obtained from NCBI.

SEM studies revealed eight types (areolate, colliculate, ocellate, papillate, reticulate, ruminate, tuberculate and verrucate) of sculpture on the surface of the seeds and these types were found in species across different clades of the phylogenetic tree, indicating that the seed coat patterns of the examined specimens exhibit significant convergence. Our results revealed that the only synapomorphic characteristic for members of Noccaea s.l. is their non-ribbed seed surface, in contrast to the ribbed seed surface found in T. arvense.

This research suggests that macro- and micromorphological characteristics of seeds are typically specific to individual species rather than to entire genera. Therefore, generic classifications based solely on seed characters may lead to inaccurate phylogenetic conclusions.