In 1973 R.S. Irving and R.P. Adams expanded on a major finding in Irving's 1968 dissertation, the correlation between the scent–producing volatile terpenoid components and clearly recognizable freshly collected taxa (recognizing at that time H. reverchonii var. reverchonii and H. reverchonii var. serpyllifolia as distinct from H. drummondii). The basic results were (listing only the major, scent–determining components):
Irving & Adams further note (192):
Although there is quantitative variation found both within and between populations, the overall quantitative and qualitative profile remains invariable.The scent correlation, which has become the basis for recent keys only after Irving's work (and his 1980 key), seems to remain unknown in spite of the difficulties of identification solely based on morphological traits. At times it is not ignored, but isn't used for want of a reliable sense of smell when collections are made. Even labels for early Irving collections failed to note a scent.
I find the work of Irving & Adams on monoterpenes compelling, and it corresponds to my own field experience with these taxa.
If it is correct:
|mint||camphor||lemon||no specific |
In effect only 8 percent of the 443 holdings in TEX/LL have a specific scent noted; and a third of these appear to have the wrong scent for the determined taxon. Less than a third of Irving's 69 collections are accompanied by a scent notation.
Most scent mismatches are for H. drummondii. In my opinion there may be several reasons for this: