Trichome characters distinguish morphological groups
A PCA of all assessed morphological characters (Tables S2 and S3)
separates the specimens rather well. The first component (PC1) separated
the cultivated M. spicata from the other mints, while PC2
separates the two native mints (M. longifolia and M.
suaveolens ) with the hybrid M. × rotundifolia (M.
longifolia × suaveolens ) falling intermediate (Figure 1a). However, the
separation between M. longifolia and M. ×rotundifolia is not very clear (Figure 1a). Five specimens were
identified as M. × villosa (M. suaveolens ×spicata ), one as M. × villosa-nervata (M.
longifolia × spicata ), and one as M. capensis , a
South-African close relative of the EurasianM.longifolia /M.spicata (Figure 1). Although the clustering
of specimens in the morphological space is overall consistent with
current taxonomic assignment, the distinction of M. spicata is
largely driven by trichome characters and when these are removed there
is a much more cloud-like projection (Figure 1b). There is however, a
tendency for the taxonomic units to roughly separate on the first PC
with M. × rotundifolia intermediate to M.
longifolia and M. suaveolens (Figure 1b). The importance
of trichome morphology is particularly evident when only characters of
indumentum are considered which results in a projection of specimens
resembling that of the overall analysis and where the first PC explains
as much as 53.3% of the variation among specimens (Figure 1c).
Distribution analyses of the indumentum characters show that the two
wild taxa have large variations in characters of indumentum, withM. longifolia generally being more ‘hairy’ than M.
suaveolens , and branched trichomes are almost exclusively found in the
latter (Figure S1 and S2). However, while the hybrid M. ×
rotundifolia show large variation in indumentum with distributions
mostly resembling that of M. longifolia , the widely cultivatedM. spicata shows less variation and is less hairy, mostly with
distributions outside of the ranges of the native taxa (Figures S1 and
S2).