Toxic compound, morphology, biology, and phenology of the calcinogenic plant Nierembergia rivularis Miers (Solanaceae).

Enzootic calcinosis caused by Nierembergia spp. (Solanaceae) poisoning causes important economic losses for sheep and cattle production in South America. This study aims to provide a comprehensive description of N. rivularis Miers, focusing on its morphological characteristics, biomass distribution, dry matter content, phenological cycle, floral biology, environmental growth preferences, and the presence of potentially toxic compounds. The results revealed that N. rivularis is a perennial, small-sized plant whose stems are modified into underground rhizomes. These subterranean structures feature nodes from which adventitious roots emerge, functioning as the primary mechanism for clonal asexual reproduction. Its white, pentamerous flowers display capitate trichomes in the corolla throat and a long, firm corolla tube that positions the corolla semi-parallel to the soil. Two insect species were observed interacting with flowers of N. rivularis, both during the spring season: Astylus quadrilineatus (Melyridae) and a small bee from the family Apidae, subfamily Apinae, tribe Tapinotaspidini. The plant exhibited a belowground biomass (rhizomes and roots) up to 15 times greater (dry weight based) than its aerial structures (leaves and flowers). The greater presence of N. rivularis in the fields was associated with high soil humidity, direct sunlight exposure, mixed soil texture, and low competition from rhizomatous species for underground space. Hydroxylated vitamin D derivatives were detected by HPLC in all structures of N. rivularis, suggesting this species' capacity to accumulate calcinogenic substances. Knowledge about the toxic compounds, morphology, biology, and phenology of N. rivularis will contribute towards the prevention and control of poisoning by this plant.