Plants native to the western coasts of Europe (from northern Spain to northwest Germany, north Ireland, and Great Britain) are treated as Asparagus officinalis subsp. prostratus (Dumort.) Corb., distinguished by its low-growing, often prostrate stems growing to only 30–70 centimetres (12–28 in) high, and shorter cladodes 2–18 mm (3⁄32–23⁄32 in) long.[5][11] It is treated as a distinct species, Asparagus prostratus Dumort, by some authors.[12][13]

Chemistry

Asparagus foliage turns bright yellow in autumn.
Certain compounds in asparagus are metabolized to yield ammonia and various sulfur-containing degradation products, including various thiols and thioesters,[14] which following consumption give urine a characteristic smell.

Some[15] of the volatile organic compounds responsible for the smell are:[16][17]

methanethiol
dimethyl sulfide
dimethyl disulfide
bis(methylthio)methane
dimethyl sulfoxide
dimethyl sulfone
Subjectively, the first two are the most pungent, while the last two (sulfur-oxidized) give a sweet aroma. A mixture of these compounds form a "reconstituted asparagus urine" odor. This was first investigated in 1891 by Marceli Nencki, who attributed the smell to methanethiol.[18] These compounds originate in the asparagus as asparagusic acid and its derivatives, as these are the only sulfur-containing compounds unique to asparagus. As these are more present in young asparagus, this accords with the observation that the smell is more pronounced after eating young asparagus. The biological mechanism for the production of these compounds is less clear.[citation needed]

The onset of the asparagus urine smell is remarkably rapid while the decline is slower. The smell has been reported to be detectable 15 to 30 minutes after ingestion[19][20] and subsides with a half-life of approximately four hours.[21]