Tibouchina /ˌtɪbuːˈ Aubl. Is a Neotropical flowering plant genus in Melastomataceae Juss. that contains approximately 240 species. Species of this genus are herbs, shrubs or trees and typically have purple flowers. They are native to Mexico, the Caribbean, and South America where they are found as far south as northern Argentina. Members of this genus are known as glory bushes, glory trees or princess flowers. The name Tibouchina is adapted from a Guianan indigenous name for a member of this genus. A recent systematic study has shown that this genus is paraphyletic.
Members of Tibouchina sensu lato are diagnosed by a number of traits including pentamerous flowers with anthers having developed pedoconnectives (the connective tissue below the anther locules) and anther appendages that are ventrally bi-lobed. These traits are likely plesiomorphic in the core Melastomeae. The magenta or purple flowers are often showy, and the stamens may be dimorphic. Members of Tibouchina have simple leaves that lack stipules with the conspicuous ladder-like venation that is characteristic of most melastomes. As a member of Melastomeae, Tibouchina also has capsular fruit and cochleate seeds.
Distribution and invasive potential
All 240 species of Tibouchina s.l. are native to the Americas as far north as Mexico, with a large proportion found in Brazil. Many species of Tibouchina s.l. are found in the Mata Atlantica in eastern Brazil, while many others are found in the cerrado and campos rupestres. Members of Tibouchina sensu stricto tend to be found in lowland savannas and on the lower slopes of the Andes. All Tibouchina species are considered noxious weeds in Hawaii because of their high potential for being invasive species. Within Tibouchina s.s., many species, such as T. papyrus, T. araguaiensis, T. nigricans and T. mathaei, have narrow distributions, being known from only a handful of locations, while a few other species, including T. aspera, T. barbigera, and T. bipenicillata, have broader distributions.
Several species are cultivated for their large bright flowers. As tropical plants they are rather cold-sensitive, and should be raised in a greenhouse wherever temperatures fall below 8 °C to 10 °C. One species, Tibouchina lepidota ('Alstonville'), known for its brilliant display of flowers in late summer and autumn is common in many parts of Australia. In Australia, both this species and Tibouchina grandiflora and cultivars are commonly known as Lasiandra. They are closely related to a native shrub Melastoma affine also known as Native Lasiandra. All these plants are featured and celebrated in the annual Lasiandra Festival held in the small country town of Wauchope, which is situated in the hinterland of the Central New South Wales Coast, City of Port Macquarie. Bright purple, the colour of the flowers, forms the central theme of the festival.
Over 30 species of Tibouchina s.l. have chromosome counts published. There is evidence for polyploidy in this group as the haploid number tends to fall in one of three classes: n=9, n=18 or n=27. This series of x=9 is quite consistent within Tibouchina although there are three documented deviations from this pattern. T. lepidota (Bonpl.) Baillon has been reported to have 2n =122 and n=62 in different studies, while T. semidecandra (DC.) Cogn has 2n =54 and T. urvilleana (DC.) Cogn has 2n =56. For species with chromosome counts, tetraploidy is most common (16 species) while 10 species are diploid and 4 species are hexaploid.
A phylogenetic analysis based on molecular data (2 plastid and 1 nuclear regions) determined that the traditional circumscription of Tibouchina is paraphyletic. Four major clades were resolved within the genus which are supported by morphological, molecular and geographic evidence. The type species, Tibouchina aspera Aubl. Was first described in 1775 based on a specimen from French Guiana. Based on the traditional code of nomenclature, the clade that the type species falls in retains the name of the genus; therefore, the clade containing Tibouchina aspera is called Tibouchina sensu stricto. A taxonomic revision of the other clades of Tibouchina s.l. and related genera has not been published.