I suggest you to investigate species of the genus Parthenium, such as Parthenium rollinsianum, Parthenium argentatum, Parthenium cineraceum, Parthenium confertum, Parthenium fruticosum, Parthenium schottii, since these species contain high amount of mucilage.
You may go for Cocculus hirsutus, seeds of all varieties of Tulsi , Aloe vera ,Lepidium sativum, Plantago ovata. I hope the information may be useful for you. Wish you all the best for your research work.
but theas days, the major problem is preparation of them from natural lands, in the latest years crises such as drought has had destructive effect on seed dispersal and plant population in Iran, especially medicinal plant and it has made it difficult for me to collect their seeds i needed.
As you have mentioned you need different species from single genus, so you may go for ocimum species, however I would have suggested some more plants if you had cleared your purpose.
I have defined a project to assay salt and drought tolerance in different species of single genus (or different genotypes of single species) and finally,I'm going to investigate the effect of mucilage to improve germinablity under thease Stressful situations.