Nettle seed

Stinging Nettle is a perennial that is not easily forgotten by anyone who has come across its path.  As the name suggests, it inflicts an itchy sting when brushed against.  The stems of the plant are covered with tiny hairs, many of them capable of injecting a chemical mixture of serotonin, acetylcholine and formic acid.  It also releases histamine, which explains the itchy side effect.  Most would consider the sting tolerable, although possibly quite a nuisance if inflicted unexpectedly.  To some, it may even be considered a sort of novelty entertainment.