Some interesting plants that might be worth researching in relation to dreaming/lucid dreaming include: mugwort, damiana, valerian, khat, calea zacatechichi, wild lettuce, passion flower, yohimbe, ephedra, clary sage, salvia divinorum, hops, kava kava and many more.
There is a particular paperback on the subject titled Drugs of the Dreaming: Oneirogens: Salvia divinorum and Other Dream-Enhancing Plants by Gianluca Toro and Benjamin Thomas. However, I found it particularly lacking. There is certainly oodles of information in relation to dreaming and plant substances. However, I have yet to see it in satisfactory book form.
In addition to simply taking a substance, there is the issue of when a substance is taken and under what circumstances. In the case of a more stimulating plant, one possible route is for an individual to only engage in the practice after four hours of deep sleep. This may allow the said individual to be tired enough to fall back asleep while the stimulant slowly started working its effects. However, if one partook of the plant simply before bed, then one might not be able to sleep at all until the effects wore off. By that point, one’s body might be so exhausted that any chance of lucidity would be dreadfully cut short.
In other words, finding a correct plant substance that facilitates lucid dreaming is not as simple as ingesting a pill and expecting results. Not only that, but every individual’s chemical makeup ensures that different plants will not affect everyone in the same manner. Nonetheless, it is certainly an interesting topic and one that warrants further investigation.