Succulent leaves are common in drought-tolerant plants from arid environments but they are not a feature of many plants that are native to Britain's cool, wet summers. This plant, biting stonecrop Sedum acre is an exception. Its small but fleshy, water-retentive leaves allow it to survive long periods of drought on wall tops, roofs, gravel and sand. It also regenerates very easily from small pieces of stem or even from single leaves, so can spread quite quickly once it has established itself.
It probably gets some of its water from nocturnal dew formation during long, dry periods (remember those?) and as long ago as 1776 the botanist and doctor William Withering speculated that this is how it obtained water. "This plant continues to grow when hung up by the root," he wrote, "which is proof that it receives its nourishment principally from the air, as is the case with most of the succulent plants".
Withering recommended its use in medicine, with some reservations, noting that " It is very acrid. Applied externally it blisters. Taken inwardly it excites vomiting. In scorbutic cases and quartan Agues it is an excellent medicine under proper management."
The acrid, peppery taste is where the 'biting' part of the common name comes from and in Withering's day it was known as pepper stonecrop.
Biting stonecrop produces a very fine display of starry yellow flowers that are popular with bees and you can cultivate the plant on almost any hard surface where a little dusty humus accumulates. The plant below was growing on bare, rusty metal in the angle of a bridge support and the bottom image shows the plant on a harbour wall in Sunderland.