Seed structure and its taxonomic implications for genus Thlaspi sensu lato sections Nomisma, Thlaspi, and Pterotropis (Brassicaceae)

Abstract

We studied morphological and anatomical characteristics of seeds of 22 taxa in the sections Nomisma, Thlaspi, and Pterotropisof Thlaspi sensu lato from Turkey and the significance of these characters in a taxonomical context. The results show that the taxa differfrom each other in terms of seed shape and color. The seed size ranges from 1.25 mm to 2.99 mm in length and from 0.66 mm to 2.16 mmin width, Thlaspi rosulare and T. tatianae having the largest and T. annuum having the smallest seeds. The seed surface ornamentationis classified into nine types: reticulate-areolate, scalariform, reticulate, reticulate-foveate, ruminate, ocellate, tuberculate, areolate, andcolliculate. The most common type is reticulate-areolate, whereas areolate, colliculate, ocellate, and tuberculate ornamentation typeswere found to be taxon-specific. The testa is typically made up of four layers: the epidermis, the subepidermis, the sclerotic (or palisade)layer, and the parenchyma layer. The sclerotic (or palisade) layer may not be seen in some of the species. The structures and thicknessesof the epidermis, the subepidermis, the sclerotic (or palisade) layer, and the parenchyma layer are highly significant characters thatreveal interspecific relationships within the examined taxa. The results are also compared with Meyer’s findings and classification of1973, 1979, 1991, and 2001, and taxon transfers are questioned. In addition, a key is provided for the identification of the examined taxabased on seed characteristics.