It's not what you may think: it's a rough botanical sketch of a fungus, not you-know-what. This did not deter Henry David Thoreau from railing about it's alleged indecency:"Pray, what was Nature thinking of when she made this? She almost puts herself on a level with those who draw in privies." Even the scientists who named it called it "Phallus impudicus" (the shameless phallus).
This says much more about the mindset of those who responded to the picture in horror, than it does about the moral standing of "Nature". I was immediately reminded of an observation I heard a few days in a BBC radio broadcast I regret I cannot recall the program, the full context, or the speaker's name).
The speaker was reflecting on the modern fuss over parents who dress their children in inappropriately suggestive clothing early age - for example, by putting young girls into padded bras. He observed that the Romans were far less concerned about such matters, and stated that in some (recent?) archaeological finds, some gold rings had been discovered,clearly intended to adorn the fingers of children, which used as deooration - images of penises