Salvia, with over 900 species from
both the Old and New World, is the largest genus in the Lamiaceae.
Unlike most members of the subfamily Nepetoideae to which it belongs.
Only two stamens are expressed in Salvia. Although the structure
of these stamens is remarkably variable across the genus, generally
each stamen has an elongate connective and divergent anther thecae
which form a lever mechanism important in pollination.
In a preliminary investigation of infrageneric relationships within
Salvia, the monophyly of the genus and its relationship to other
members of the subfamily Nepetoideae was investigated using the
chloroplast DNA regions rbcL and trnL-trnF. This project will be
significantly expanded both in sampling of taxa, to include most
genera of the Mentheae, and genomic regions. Some of the preliminary
results are presented here:
Salvia Clade I:
With the exception of those species included in Clade III, all Old
World Salvia form a monophyletic lineage sister to Rosmarinus and
Perovskia. Included in this clade are four New World species of
sect. Heterosphace and three species in subgenus Salviastrum.
New World members of Clade I:
In the New World, there exist four lineages of Salvia. Subgenus
Audibertia, subgenus Calosphace, section Salviastrum, and section
Heterosphace. Salviastrum, consisting of three species native to
Texas and northern Mexico, was originally placed by Scheele (1849
Linnaea 22:584) in its own genus. Although expressing the elongate
connective diagnostic of Salvia, Scheele elevated Salviastrum to
its own genus based on a dense annulus in the calyx. Torrey (1859)
soon thereafter noted the close affinities of Salviastrum and Salvia
sect. Heterosphace and included Salviastrum as a section within
Salvia. Bentham (1876) however, agreed with Scheele and maintained
Salviastrum as its own genus. The most recent treatment of Salviastrum
(Whitehouse 1949) agrees with Torrey’s treatment and states,
“except for the dense ring of hairs in the calyx throat…there
are no common differences with will separate them from other species
of Salvia. If the species included in Bentham’s section Heterosphace
are included in Salvia, then undoubtedly the Salviastrum section
should be included, for they are closely linked by their similar
calices which are alike in form and accrescence…”
The molecular data, supporting a monophyletic lineage consisting
of Heterosphace + Salviastrum clearly support the suggestions of
Whitehouse. The molecular phylogeny suggests a single dispersal
event from the Old World to the New, with subsequent diversification
to the four species of Heterosphace and three species of Salviastrum
in the New World. It is of interest to note that remaining members
of Heterosphace are southern African. The molecular analyses suggest
a close relationship between Heterosphace, Salviastrum and southern
African taxa, although the exact relationship between these groups
awaits further analyses.
Salvia penstemonoides Kunth et Bouche is a narrowly endemic species
native to south-central Texas, thought to be extinct until its rediscovery
in 1987 (Clebsch 1997). Originally described as belonging to Bentham’s
section Eusphace (Kunth et Bouche 1848), its rbcL sequence is exactly
the same as Salvia texana, clearly suggesting its affinities with
sect. Salviastrum. Its calyx (although lacking an annulus) and leaf
morphology are more similar to Salviastrum than any other New World
Salvia. If Salviastrum is maintained as its own section (albeit
a paraphyletic taxon), S. penstemonoides should be included within
it.
Salvia Clade II:
Audibertia – Calosphace relationships. Whereas Bentham (1876)
included Calosphace as part of Salvia, he treated Audibertia as
an entirely separate genus. Epling, whose revision of Calosphace
(1939) remains the most complete treatment of the subgenus, felt
that Audibertia and Calosphace were closely related (Epling 1938).
Kurt Neisses (1983), who investigated relationships within Audibertia
based on morphological, chemical and pollen characters suggested
Audibertia not allied with Calosphace and more closely related to
Rosmarinus and Old World groups of Salvia included in Bentham’s
subgenus Leonia. An analysis of megagametophyte types in Salvia
(Carlson & Stuart 1936) also suggests Old-World affinities of
Audibertia, as do chromosome studies on the genus (Epling et al.
1962).
Our molecular data clearly demonstrates a monophyletic Calosphace,
sister to either Audibertia, or the monotypic Asian genus Dorystoechas.
Dorystoechas/ Audibertia/ Calosphace is well supported as monophyletic,
and most likely sister to an eastern Asian group of Salvia (Salvia
clade III).
Salvia Clade III:
One of the more surprising results of this project is the existence
of what is potentially a third clade of Salvia. Each of the species
in this clade are east Asian plants corresponding to Bentham’s
section Drymosphace. Drymosphace is defined by being large, herbaceous,
glutinose plants with hastate leaves, the upper lip of the calyx
short tridentate, a falcate, often compressed corolla and connivent
posterior anther thecae, stretched forward. An expanded rbcL analysis
suggests this clade likely includes additional species outside Drymosphace.
Future inclusion of these taxa in a combined analysis will hopefully
illucidate the conscription and help to define both the morphological
characters defining the clade, as well as the relationship of the
clade to the remainder of Salvia and Mentheae.
Molecular Systematics |