It coincides with part of the much longer Beestonian stage in Britain.
Its name is derived from a major branch of the Rhine delta, the Waal.
[6][7] The Waalian Interglacial is also distinct from later interglacial periods in that the migration of tree species during this period did not follow a clear pattern of succession (i.e., most of the species that were present at the end of the Waalian were there at the beginning).
[5] In addition, though earlier research indicated that the forest species assemblage of the Waalian period mirrored that of the Tiglian,[6] more recent research into pollen records show that there was a marked decrease in the number of arboreal taxa from earlier Pleistocene periods.
[8] Common arboreal taxa from the Waalian period included Tsuga, Eucommia, Celtis, and Pterocarya.