Medicinal and aromatic plants – industrial profiles

Taxonomic treatment
The species and infraspecific taxa are arranged according to sections. Those whose sectional 
position is uncertain are dealt with at the end. Hybrids have been dealt with under each section
except for intersectional hybrids which are placed after the sections. Keys to the species are
given under each section. Only the most important synonyms are given as appropriate for each
species and placed in brackets 
as appropriate
. Author abbreviations follow Brummitt & Powell
(1992).
Sectional classification
Although the species exhibit a wide variation of morphological characters, it is evident that 
natural groupings of related taxa can be recognised. These groups have been classified as 
sections, of which there are six presently recognised. It seems likely that further groupings need
to be recognised and current work is presently aiming to confirm this. The sections can be 
distinguished by differences in habit, leaf shape, the arrangement of the flowers in the verticils,
bract, calyx and corolla characters (Figures 2.1–2.5).