Pollen morphological studies revealed the occurrence of the characteristic spinulose pollen type ofKoenigianot only in the three species earlier recognized in the genus (K. islandica,K. nepalensisandK. pilosa) but also in three additional species earlier treated underPolygonum, viz.K. delicatula(Meisn.) Hara,K. forrestii(Diels) Mesı́cek & Soják, andK. nummularifolia(Meisn.) Mesı́cek & Soják. Further studies of flower morphology, fruit and petiole anatomy, basic chromosome number, etc., revealed additional similarities between those species, which led to a taxonomic revision of the genusKoenigia. This genus seems to be most closely related toPersicariaMill. sectionsCephalophilon(Meisn.) Gross andEchinocaulon(Meisn.) Gross, withKoenigia delicatulaas a connecting link. There are also interesting similarities with the genusAconogonon(Meisn.) Rchb.Koenigiaexemplifies the derivation from montane ancestors of a high mountain-dwelling genus displaying adaptive radiation to fit diverse alpine niches. Five species out of six are confined to high mountain areas in southeastern Asia, primarily in the Himalayas, whereas the sixth has spread to Arctic and alpine areas in the northern hemisphere and even penetrated to southern South America. The latter species shows progressive reduction in size in combination with adaptation to a very short summer under severe climatic conditions.