It has been pointed out that fungi can act as aids to higher plant classification. The results of inoculation tests with the rust fungus Puccinia paullula f. sp. monsterae are examined in relation to the placement of the taxa in the classifications of the taxonomic and molecular botanists. Out of 72 plant taxa inoculated over a period of years, 64 were immune and eight showed various degrees of susceptibility. Of these eight, seven (Monstera deliciosa, M. standleyana 'Variegata', M. adansonii var. laniata, M. obliqua, M. subpinnata, Stenospermation sp. and Epipremnum pinnatum) are all in the tribe Monstereae of the subfamily Monsteroideae. The eighth, Typhonodorum lindleyanum, the giant swamp taro of Madagascar and East Africa, which is placed in the tribe Peltandreae of a different subfamily (Aroideae), was also found to be moderately susceptible. These eight taxa belong to four genera with present natural geographic distributions in Africa, America, Asia and Australia. Apart from the seeming anomaly of Typhonodorum which may be further evidence of ancient aroid germplasm distribution- the taxa with various degrees of susceptibility to the Monstera rust fungus do reflect affinities as given by the taxonomic and molecular botanists.