Seed morphology and endosperm structure of selected species of Primulaceae, Myrsinaceae, and Theophrastaceae and their systematic importance

Abstract

Seed size and shape, seed coat surface pattern, seed coat thickness, and endosperm structure were investigated in Androsace septentrionalis, Cortusa matthioli, Hottonia palustris, Primula elatior, Soldanella carpatica (Primulaceae), Anagallis arvensis, A. minima, Cyclamen purpurascens, Glaux maritima, Lysimachia nemorum, L. vulgaris, Trientalis europaea (Myrsinaceae), and Samolus valerandi (Theophrastaceae). Three seed size categories were distinguished on the basis of biometric measurements. Almost all seeds examined were found to be small with an angular shape classified as sectoroid or polyhedral. A new type of seed shape, suboval, was identified for H. palustris. Cyclamen purpurascens seeds differed from seeds of all other species examined because of their large size, subglobose shape, and concave hilar area. Despite the different shape types, the length/width ratio of the seeds examined was constant, while their hilum length/width ratio was a highly variable feature. Three types of seed surface patterns were observed: (1) reticulate, (2) tuberculate with secondary striations, and (3) poroid-alveolate with the presence of a spongy outer layer. For seeds of Anagallis arvensis, A. minima, Cortusa matthioli, Lysimachia nemorum, and Soldanella carpatica, secondary seed sculpture was described. The seed coats of all species examined were two-layered, and great differences in testa thickness were found (9.9–128.6 μm). In general, seeds of the Myrsinaceae species were more often characterized by thick testa. Different proportions in thickness of the inner and outer testa layers were observed. In seeds with reticulate seed patterns, the inner testa layer was twice to several times thicker than the outer layer, while the opposite proportions were observed in seeds with the tuberculate or poroid-alveolate seed sculpture pattern. In seeds of all species examined, oxalate crystals were present on the surface of the inner testa layer. Thus, the presence or absence of oxalate crystals in testa is not a feature distinguishing species with angular or subglobose seeds. Four types of endosperm structure were identified according to the thickness of the endosperm cell walls and the relief of their inner surface: (1) with evenly thickened and smooth cell walls, (2) with evenly thickened cell walls and circular or helical thickenings on their inside surfaces, (3) with very thick, but not evenly thickened cell walls with constrictions (“pitted”), and (4) with very thin papery and undulate cell walls. There is no rule concerning the seed shape, type of the seed sculpture, testa thickness, or endosperm structure that corresponds to the family affiliation of the species examined.