This paper is a part of the outcome of a systematic study of unnamed specimens in
the family Labiatae accumulated in recent years. The genus, Microtoena, was established
by Prain in 1889. The first species published, M. cymosa Prain should be designated as
the type of this genus, but the name was antidated by Clarke’s Plectranthus patchouli, so
that the new combination M. patchoulii (C. B. Clarke) C. Y, Wu et Hsuan should now
replace M. cymosa as the type. Up to date, Microtoena consists of 20 species and 5
varieties confined to tropical and subtropical regions of southeastern Asia. With regard
to the distribution, Yunnan has the greatest concentration of species. 10 species and 4
varieties so far having been found in that province, totalling more than half of the known
constituents of this genus accredited to our region. The genus has no representative
beyond latitude 32° North.
Microtoena patchoulii (C. B. Clarke) C. Y. Wu et Hsuan and Microtoena mollis
Lévl. are closely related with Microtoena insuavis (Hance) Prain and were reduced into
the latter by many authors, but according to their morphological characters (according to
the original descriptions) and distribution they are distinct from that species.
Based upon the characters of calyx lobes and the shape of the middle lobe of the
lower labium of the corolla, we arrange the species in this paper into 5 series.
We are of the opinion that Microtoena? coreana Lévl. is possibly a species of another
genus, while Microtoena urticifolia var. subedentata Hand.-Mazz. is perhaps another
species of the genus.
