This study provides the first complete taxonomic revision for one of the five
subgenera of Tradescantia, proposed by Pellegrini (2017). A taxonomic revision
for T. subg. Austrotradescantia is presented, based on extensive field,
cultivation, and herbaria studies. Thirteen species are recognized, most of them
being widely distributed and presenting considerable morphological variation. The
observations on dried and living specimens suggest that most variation in the genus
might be ecologically related, with some changes being also putatively controlled by
epigenetics and cytology. Out of the 13 accepted species, three of them (i.e., T.
atlantica, T. hertweckii, and T. tucumanensis) are described as
new. An identification key, distribution maps, descriptions, comments, conservation
assessments, and illustrations for all species are provided. Tradescantia
subg. Austrotradescantia as a whole seems to be in need of little
conservationist attention. Most species possess wide native distribution, with only
T. atlantica, T. chrysophylla, T. hertweckii, and T.
seubertiana possessing narrower distributions, and thus meriting some
conservationist attention. The troublesome weed T. fluminensis has its
specific limits clarified and its native range is presented so it can serve as a
basis to better understanding its ecological requirements and to help control it
throughout its invasive range. After careful examination of herbarium specimens
collected outside the groups’ native distribution range, it has been concluded that
several records of T. fluminensis as a invasive weed actually represent
misidentified specimens of T. mundula, or more rarely specimens of T.
cymbispatha and T. crassula. Tradescantia mundula might also
represent a troublesome weed worldwide. This species has been widely introduced in
cultivation under the name T. albiflora and seems to have also escaped from
cultivation. However, due to the hitherto poorly understood specific limits of T.
fluminensis, T. mundula has been regarded as a mere cultivar of T.
fluminensis s.s. Tradescantia cerinthoides is also widely cultivated
worldwide, especially its pink and lilac-flowered morphs. Despite not having observed
any unquestionable records that indicate that T. cerinthoides has escaped from
cultivation, this species also possesses intense vegetative growth, and thus a great
potential to become an invasive species if not properly monitored. All invasiveness
accessions done do far for T. fluminensis must urgently be redone in order to
properly understand the extension of this species’ invasion, discount records now
known to represent other species from the subgenus, and appropriately access the
threat of invasiveness of the other species of T. subg. Austrotradescantia
which also possess records outside their native range.