LINDQVIST, CHARLOTTE* and VICTOR A. ALBERT. Biodiversity and Systematics, Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL 35487-0345. - The Hawaiian endemic mints are derived within North American Stachys (Lamiaceae).
The three Hawaiian endemic mint genera, Haplostachys,
Phyllostegia, and Stenogyne (Lamiaceae), had been
thought to be closely related to East Asian members of tribe Prasieae
because of the fleshy nutlets borne by the latter two genera.
Phylogenetic analyses of chloroplast rbcL and 5S nuclear
ribosomal non-transcribed spacer (5S-NTS) sequences supported the
monophyly of the Hawaiian mints and indicated that a North American
Stachys species was a closer relative. We present further
refinement of this hypothesis based on a phylogenetic survey of North
American Stachys 5S-NTS sequences. As previously found, the
Hawaiian clade consists of Haplostachys sister to
Phyllostegia plus Stenogyne, which are unresolved with
respect to each other. However, the Hawaiian taxa, which are
characterized by chromosome number 2n=64 or 66, are deeply nested
inside North American Stachys, their closest relative being
Stachys rigida, a strictly western North American species with
2n=66. Stachys rigida plus the Hawaiian mints are related to a
larger clade of Stachys species, some of which are found mainly
in the southeastern part of the United States and have 2n=34 and/or
68, whereas others are endemics of western North America with 2n=66.
In turn, this larger group is sister to two clades representing taxa
from Texas through Mesoamerica, one of which has chromosome number
2n=32, the other 2n=80-84. The relationships between North American
and Eurasian Stachys taxa are still unclear but preliminary
rbcL data suggest that they may represent separate lineages.
The chromosome number 2n=66 recorded for Stachys rigida, other
western Stachys, and some Hawaiian mints has previously been
explained by centric fusion from 2n=68, but could instead be
indicative of allopolyploidy between n=32 and n=34, which in turn
could help explain the radiative evolution of morphological features
in the Hawaiian endemic mints.
Key words: Hawaiian mints, molecular systematics, morphological radiation, polyploidy, Stachys