https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:119000-1
M. discolor s.s. is an hexaploid taxa derived from diploid M. dubia
Therefore dubia can't be considered as subsp. of discorlor s.s. and following POWO treatment as distinct species is appropriated.
See also https://www.arb-idf.fr/fileadmin/DataStorageKit/ARB/Publications/arb_cytotaxonomie_complet.pdf p.41