Cnidoscolus stimulosus

Todays Botany Photo of the Day comes courtesy of Bruce Vanderveen aka duneaster@Flickr (original via UBCBG BPotD pool). Check out his collection of native plant photos from Florida.

Who could suspect this dainty member of the Euphorbiaceae of being such a menace? A flower has never looked so appetizing, bearing such close resemblance to a piece of floral confectionary from some wedding cake. However, with such suggestive common names as finger rot and tread softly, it''s no surprise that this plant isn''t found on cakes or in bouquets. As can be seen from today''s image, Cnidoscolus stimulosus is covered in trichomes. In the case of Cnidoscolus stimulosus, these small hairs will irritate the skin upon contact. Regarding tread softly and other plants which possess such weaponry, Nancy C. Coile writes,

"The urticating hair or trichome has a bulbous and very fragile tip which breaks off at an angle and results in a perfect tool for piercing skin. Basically, the shaft of the hair resembles a glass tube due to the deposition of silica in the cell wall during formation (Thurston 1974). When the urticating hair tip is broken, it has the action of a hypodermic needle and injects the urticating substances which cause the intense pain and result in irritated skin rashes." (from Florida''s Department of Agriculture - Urtica chamaedryoides Pursh: a Stinging Nettle, or Fireweed and Some Related Species - PDF).

Cnidoscolus stimulosus is often mistaken for the true stinging nettle, Urtica dioica. The latter has a near world-wide distribution while finger-rot is confined to the southeastern United States. As far as the urticating substances in Cnidoscolus stimulosus are concerned, I can only guess that they might include those found in Urtica dioica such as histamine, acetylcholine, and serotonin (from the previously mentioned article). Posted by: Daniel Mosquin    Source