1. Proceeding from natural feeling or impulse without external stimulus
   - impulsive

See also: self-generated, spontaneous

• genus Simulium
• genus Sinanthropus
• genus Sinapis
• genus Sinningia
• genus Sinornis
• genus Siren
• genus Sison
• genus Sistrurus
• genus Sisymbrium
• genus Sisyrinchium
• genus Sitophylus
• genus Sitotroga
• genus Sitta
• genus Sium
• genus Sivapithecus
• genus Sloanea
• genus Smilax
• genus Smiledon
• genus Smyrnium
• genus Sobralia
• genus Solandra
• genus Solanopteris
• genus Solanum
• genus Solea
• genus Soleirolia