After Onobrynchis aliacmonia Rech.f. was considered to be extinct due to the construction of a dam in the Aliakmon river that flooded its original site of occurrence, Greuter (1987) found a very similar species in a completely different habitat in the Peloponnese, and reported it as Onobrychis aliacmonia. After studying new collections of individuals from the Peloponnese, Tan and Iatrou (1996) classified this as a new subspecies, Onobrychis aliacmonia subsp. peloponnesiaca. However, in 1999 Greuter and Raus published it as a different species, Onobrychis peloponnesiaca (Iatrou & Kit Tan) Iatrou & Kit Tan, and was finally accepted by Dimopoulos et al. in 2013. Currently, Plants Of the World Online (2019), International Plant Name Index (2020) and Flora of Greece (Dimopoulos et al., 2020) accept both names as different species: Onobrychis aliacmonia for the northern species from Polifitou Lake, and Onobrychis peloponnesiaca for the southern species.

Onobrychis aliacmonia is only known to be present in both lakesides of Polifitou Lake, in the Kozani area, Greek Macedonia (Greece) (Tan and Iatrou 1996). Its area of occupancy (AOO) and extent of occurrence (EOO) are estimated to be 20 km². The main threat for this species are the changes in the water level of the lake, which result to temporary flooding and emergence of parts of the lake shore. The water level is the factor that led the species to near extinction a few decades ago and it remains a threat and is therefore considered a single location. Extreme population fluctuations have been reported for this species (Tan and Iatrou 1996), which has become locally extinct in the past in areas close to the lake due to flooding. There is also pressure on the species due to grazing, but this does not seem to threaten it with extinction. The species may occur in other localities further away from the shores at higher elevations, but this is not confirmed and not known whether these face threats and if they had disappeared in the past. Onobrychis aliacmonia had been declared extinct despite repeated visits in the area to relocate it, but there has never been a thorough study of the species' distribution and its temporal dynamics. Based on the EOO, the low number of locations (one) and the extreme population fluctuations caused by the changes in water level, O. aliacmonia is assessed as Critically Endangered CR B1ac(iv). More research is needed to further evaluate the threats to this species, as well as to determine population trends and its presence elsewhere.

Onobrychis aliacmonia is an endemic species to the Aliakmon valley, in western Greek Macedonia. It was first described as inhabiting the side of the road from Servia to Kozani, north of the bridge that crossed the Aliakmon river (Greuter 1987). Around 1973-1974, the building of a dam in the river created the artificial Polifitou Lake, thus flooding the original habitat of this species, which led to it being classified as Extinct by IUCN in 1982. However, in 1996 it was reported as growing in both sides of the lake, surrounding the road from Servia to Kozani (Tan and Iatrou 1996), therefore leading to the species being removed from the Extinct category. The area of occupancy (AOO) and extent of occurrence (EOO) were calculated using estimated coordinates based on the habitat description by Tan and Iatrou (1996), Flora Hellenica (Strid, A. pers. comm. 2022, Flora Hellenica Database) and observations (Stefanaki and Goula 2014, Goula 2018). The area of occupancy (AOO) is estimated to be 20 km², and the raw extent of occurrence (EOO) value is estimated to be 8 km², adjusted to 20 km² to match the area of occupancy (AOO). All individuals can be considered to occur in a single locality because the changes in lake water level affect the species as a single threat.

After the flooding of the Aliakmon valley due to the construction of the dam in 1976, several attempts to relocate the species during the 1970s and 1980s were unsuccessful (Tan and Iatrou 1996). In 1994 (when this species was still considered extinct), K. Tan and G. Vold collected a specimen of Onobrychis aliacmonia from the southern side of Polifitou Lake, now deposited in the Herbarium of the Natural History Museum of Denmark. In the label, kindly provided for this study by Olof Ryding, collection manager of the herbarium, the population is described to be comprised of more than 20,000 individuals. Tan and Iatrou (1996) describe at least 30,000 individuals from a quick count. Neither of those two estimates specify if the count corresponds to a single or more subpopulations on the sides of the Polifitou Lake. The population of the species has undergone extreme fluctuations in the number of individuals ranging from apparently zero to 20,000-30,0000 due to changes in water level. More detailed surveys will help elucidate the population dynamics of this species.

Onobrychis aliacmonia's grows at Lake Polifitou's shore and hill slopes above it, at 280-300 meters above sea level, and also in the roadside, in ditches and at the edge of agricultural fields. The substrate is described to be a characteristic dry white marly soil, very common in the Aliakmon valley (Tan and Iatrou 1996). Other plant species described for the area by Greuter (1987) were: Salvia candidissima Vahl, Lotus aegaeus (Griseb.) Boiss., Scutellaria orientalis L., Goniolimon collinum (Griseb.) Boiss., Stachys iva Griseb., Bolanthus thymifolius (Sm.) Phitos, Haplophyllum coronatum Griseb., Paronychia macedonica Chaudhri, Centaurea brevispina Hausskn., Thymus atticus Celak., Astragalus cf. stella Gouan, Asperula aristata subsp. nestia (Rech. fil.) Ehrend. & Krendl, and Allium favosum Zahar; from all of these species, only A. favosum has been assessed by IUCN (as Data Deficient - DD). It is worth noting that, while those plants could be present in O. aliacmonia's current habitat, the description in Greuter (1987) corresponds to the first habitat described for this plant, which is currently flooded by Polifitou Lake.

The main threat that Onobrychis aliacmonia faces is the changes in the water level of the lake, which led the species to near extinction in the 1970s and continues to be a threat, affecting the extent of the habitat and number of individuals of the species. These changes are periodical and depend on the use of the lake water for electricity production and irrigation. They also depend on natural factors (rainfall, snow).

There is no use/trade information available for this species.

No conservation actions are known for this species. Its habitat is not included in a protected area.