When considering fruits known to be dangerous due to their toxicity, the list is relatively short compared to other plant categories. These include fruits that are inherently toxic, those that can become toxic under certain conditions, and those that are part of plants where other parts are toxic. An approximate number of such well-known dangerous fruits would be around 10 to 15 species.

This estimation includes fruits like:

• Ackee (toxic when unripe)
• Certain wild berries (like some species of nightshade)
• Unripe or inedible parts of otherwise edible fruits (like apple seeds, which contain amygdalin)

Remember, this is a rough estimate, focusing on fruits that are widely recognized for their potential dangers. The exact number can vary depending on the specific criteria used for inclusion.