First record of long-lost Ruellia bella reported in Myanmar

Ruellia is a very large genus of chiefly tropical American herbs and shrubs (family Acanthaceae) that have showy solitary or paniculate flowers with the simple or two-lobed style recurved at the apex and the two-cell ovary.

During the botanical exploration in Yinmabin District, Sagaing Region Myanmar in June 2020, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) and Monywa University collected a flowering Ruellia specimen.

After a meticulous examination of its morphology and comparison with protologues and relevant literature as well as digitized type specimens of the genus Ruellia from Myanmar and neighboring countries, the researchers confirmed it as Ruellia bella, a long-lost species known to be endemic to Thailand.

Ruellia bella was described by William Grant Craib on his "Contributions to the Flora of Siam," based on specimens collected by Arthur Francis George Kerr in 1915 in Thailand.

In a study published in Feddes Repertorium, the researchers presented the rediscovery of R. bella after a lapse of 105 years, as the species was recently found in Yinmabin District of Sagaing Region which also corresponds to its first record in Myanmar.

R. bella is a subshrub of about 10 cm tall. It is a member of the section Dipteracanthus characterized by having solitary flowers in the axils with two foliaceous bracteoles.

According to Craib, R. bella is similar to R. suffruticosa from Bangladesh and India and R. macrosiphon from lower Myanmar. However, it differs in having a longer corolla and wider leaves.

In Myanmar, the species is found growing in tropical dry forest with shaded environment at 60 m above sea level. In Thailand, it is growing in deciduous forest at 300 m above sea level.

It is observed flowering and fruiting in the wild in the month of May and June. The flowers open at night.

Following the Red List criteria of the IUCN Standards and Petitions Subcommittee, the researchers considered the conservation status of R. bella as "Data Deficient" (DD).