"Leaves of three, let it be" is the old proverb concerning Poison Ivy (Toxicodendrens radicans). This specimen is in the poisonous plants section at the South London Botanical Institute. That saying is good advice: brushing against Poison Ivy can result in a nasty and painful rash.

 T. radicans is native to North America. I remember chatting to a hiker on the Pacific Crest Trail who was in a good deal of discomfort after coming into contact with it.

 The one at the SLBI was starting to expand beyond its designated area so I was asked to thin it out. Gloves and well covered up were the order of the day- no shorts or t-shirt for dealing with this task. Poison Ivy is an example of a vine developing adventitious roots as it climbs and scrambles.