Despite the synonym
Opium Lettuce it is not related to: Opium Poppy
Related to: ordinary
Garden Lettuce. If lettuces are allowed to grow then they 'bolt' producing a long stalk and prickly leaves much like as here.
Some similarities to : Prickly Lettuce, but that has much a finer pitch of the teeth on the edge of the leaves, and the mid-rib of the leaves is not purple as in Great Lettuce, but white. Prickly Lettuce also has lighter green leaves, a green stem, and smells slightly foetid.
Possibly confusable with: Rough Sow-thistle and Smooth Sow-Thistle.
Uniquely identifiable characteristics
Distinguishing Feature :
Great Lettuce has a very stout and reddish stem, with long flexible prickles on it. The leaves are darkish green with reddish tinges and wavy edged and teeth sharpish teeth on the periphery and on the underside of the red mid-rib. The stem exudes a milky liquid when broken (but so does Prickly Lettuce).
Great Lettuce is one of the few Daisy & Dandelion Family members that has a red stripe on the rear of the outer ray florets. Others include Cat's-ear, Smooth Hawk's-Beard, Mouse-Ear-Hawkweed and Beaked Hawk's-beard.
It inhabits disturbed and waste ground, especially near the sea.
The milky sap which exudes from broken stems is not called laudenum as has been suggested elsewhere, and despite that name of Opium Lettuce being one of its synonyms, it does not contain any opiates, but rather several lactones with pharmacological properties only similar to that of opium. The latex that can be prepared from the milky sap is called Lactucarium; it was prescribed as a tincture in the 1800's for use in cough medicines and lozenges. All lettuces contain some amount of this narcotic liquor, even garden lettuce, although the consumer may have to eat considerable quantities of lettuce before any harmful effects become apparent.
The native American Hopi tribe used to smoke the dried resinous sap from the broken stems. It induced dream-like trances and lucid dreaming.
The milky sap contains the lactones Lactucin and two derivatives, Lactucopicrin and 11-,13-dihydrolactucin. Lactucopicrin has acetylcholineesterase inhibitory actions, whilst Lactucin is an agonist against the Adenoside receptors. These extracts can help induce sleep, but are also poisonous in excess, death can result.
OTHER CHEMICAL CONSTITUENTS
Great Lettuce also contains flavonoids, coumarins and
NMPEA), which is chemically similar to the manufactured pharmacological drug
NMPEA occurs naturally in humans in trace trace amounts and acts as a neuromodulator. Like the derivative
PhenylEthylAmine (PEA) it is an alkaloid. It acts similar to
Adrenaline) but exhibits only 1/350th the potency. It has similar pharmacological and toxicological properties as
PhenylEthylAmine and other Methyl-PhenylEthylAmines (or at least it does in rats, which have similar, but not identical, biological mechanisms to humans).