This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
A South European wiry and spiny-stemmed shrub 3 to 5 ft. high, with roundish glistening leaves, and white flowers 2 in. across. It can only be grown in the mildest and warmest parts of Britain. There is also a form without spines. The flower buds, known as "Capers", are gathered when as large as peas, and are pickled in vinegar.
This plant must not be confused with the "Caper Spurge" (Euphorbia Lathyris), a milky-juiced British biennial, 3 to 4 ft. high, with ovate-oblong blue-green leaves, and roundish fruits which are often taken for real "Capers". The seeds yield an extremely acrid oil, resembling croton oil in its properties, and sometimes substituted for it. The plant is very common in some cottage gardens.