It appears that the research on the subject is still quite active, and pretty much inconclusive.
For example, I present the case of the studies regarding the Tribulus terrestris :
Aphrodisiac properties of Tribulus Terrestris extract (Protodioscin) in normal and castrated rats -
K Gauthaman, P.G Adaikan, R.N.V Prasad - 9 August 2002
However, this study provides additional information as regards to
androgens and its regulation of penile erection and that the plant
Tribulus terrestris is found to exert similar properties to that of
androgens. Results of this study provide evidence for the claimed role
of this plant as an aphrodisiac in the traditional medicine.
The aphrodisiac herb Tribulus terrestris does not influence the androgen production in young men
V.K. Neychev, V.I. Mitev - 3 October 2005
Altogether, the findings in the current study anticipate that chronic
ingestion of either 10 or 20 mg/kg body weight of Tribulus terrestris
extract influence neither directly nor indirectly androgen production
in young males.
Aphrodisiac activity of Tribulus terrestris Linn. in experimental models in rats Surender Singh, Y.K. Gupta - April 2011
Oral administration of 100 mg/kg of test drug has proven anabolic
effect as evidenced by body weight gain in the body and reproductive
organs. Improvement in sexual behavior of male rats was characterized
by increased amount and intromission frequency.
In any case, the most comprehensive study I was able to find is
Pharmacologically screened aphrodisiac plant-A review of current
scientific literature Patel DK, Kumar R, Prasad SK, Hemalatha S - 28 June 2011
which reviews the studies about 30+ plants a and concludes with :
Many of the plant materials showed positive aphrodisiac activities in
animals. For the determination of the safety and effectiveness of
these substances for sexual enhancement it is necessary to test
pre-clinically in animals and clinically in human being before
consuming the drug. Further studies are also needed to check the
mechanism that underlie behind such activity