Systematics of Pogostemon Desf. (Labiatae) and related genera.
A systematic study of the genus Pogostemon Desf., and related genera, Colebrookea
Smith, Leucosceptrum Smith, Eurysolen Prain, Rostrinucula Kudo and
Comanthosphace S.Moore in subfamily Pogostemonoideae sensu Cantino, Harley and
Wagstaff, is reported. The genus Anisomeles was also included in the analysis as a
sister group to the above. A systematic account, including several new species, and with
keys is provided. A detailed morphological survey of 90 species has been carried out,
amounting to over 95% of all species of these genera. The survey, which included a
scanning electron microscope survey of nutlet surface morphology and trichome
variation, has resulted in the discovery of several taxonomically useful floral characters:
the distribution of hairs in the calyx and on the stamens, the presence of glands on the
ovary, and the shape and size of the calyx and corolla. Cladistic analysis and phenetic
analysis (cluster analysis and principal components analysis) has been carried out. A
majority rule consensus cladogram, which is supported in some respects by phenetic
results, has been used to establish a new classification of the subfamily. Anisomeles is
shown to be unrelated to the subfamily. Colebrookea Smith, Leucosceptrum Smith,
Eurysolen Prain, Rostrinucula Kudo and Comanthosphace S.Moore are shown to be
related but are placed in two tribes, the monotypic Colebrookeae and the
Leucosceptreae containing the others. A new genus Coroanthonucula ined., intermediate
between Rostrinycula and Comanthosphace, has been erected. The genus Pogostemon
is shown to be monophyletic by the possession of moniliform staminal hairs. A
subgeneric classification of Pogostemon has been established by dividing it into 4
sections; sect. Pogostemon, sect. Decaneryi, sect. Yerticillati and sect. Dysophylla.
Data is presented that suggests that the first three may be natural/monophyletic groups
but sect. DysopbyUa is a paraphyletic group of species intermediate between sect.
Verticillati and sect. Pogostemon.