Just like cincfoille and quinquefoille the word derives from Latin quinquefolium(with the latter preserving a more Latinate form of numeral) and basically has the same meaning. In this case, the numeral is replaced by the ordinal quintus. FEW, OED and DMLBS treat these as the same word (with the FEW merely acknowledging a ‘von quintus beeinflussten form’), but the forms are sufficiently different to warrant separate articles in the AND).