"Floral odor composition in Asclepiadoideae" (in cooperation with Sigrid Liede-Schuhmann and Ulrich Meve).

In some Stapelias flies are attracted by odors that are very unpleasant to the human nose but these odors seems to be very attractive to flies. For example, the floral odor of Desmidorchis flava can be described as "reminiscent of decaying urine" or "foul and urinous"

Some informationon the taxonomy of the Gentianales, especially Apocynaceae - Asclepiadoideae:

Tribe Asclepiadeae

Tribe Stapelieae

Objectives

The aim of this study is to investigate the pollination ecology and floral scent chemistry of those plant species that emit unpleasant odors (frequently equated to the odors of rotting fish, carrion, or dung), which serve as important chemical attractants for insects within the orders Coleoptera and Diptera. 

Some compounds that we have found so far in the floral odor of foetid Stapelias:

Analysis of these odors through headspace adsorption and thermo desorption (MicroSPE) followed by capillary GC and GC-MS analysis reveals the presence of indole, skatole, p-cresol, 2-heptanone, and polysulfides which impart the fecal characters in the flower scent. Acids like hexanoic acid, and heptanoic acid are responsible for the urinous character of the floral odor in Desmidorchis flava.

Polysulfides (rotten-egg, not a very nice smell)

dimethyl disulfide	dimethyl trisulfide	dimethyl tetrasulfide

Nitrogen containing compounds (dung-note, fecal, dogs know this)

indole	3-methylindole (skatole)

Acids (urinous, main compounds of Desmidorchis flava, "the yellow flower color fits to the smell")

butanoic acid	hexanoic acid
heptanoic acid	nonanoic acid

_{Andreas Jürgens}