Aphrodisiacs: Chemical agents or odors that stimulate sexual desires. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Tribulus: A plant genus of the family ZYGOPHYLLACEAE. Members contain steroidal saponins. Ingestion by grazing animals causes PHOTOSENSITIVITY DISORDERS called geeldikkop (yellow thick head) in South Africa.Lepidium: A plant genus of the family BRASSICACEAE growing in Peru mountains. It is the source of maca root.Myristica fragrans: A plant species in the MYRISTICACEAE family. The seed is used as a spice and used for antimicrobial and psychoactive effects. Myristicin, SAFROLE, and methyleugenol are key components.Penile Erection: The state of the PENIS when the erectile tissue becomes filled or swollen (tumid) with BLOOD and causes the penis to become rigid and elevated. It is a complex process involving CENTRAL NERVOUS SYSTEM; PERIPHERAL NERVOUS SYSTEMS; HORMONES; SMOOTH MUSCLES; and vascular functions.Plant Extracts: Concentrated pharmaceutical preparations of plants obtained by removing active constituents with a suitable solvent, which is evaporated away, and adjusting the residue to a prescribed standard.Sexual Behavior, Animal: Sexual activities of animals.