Burmannia unguiculata Averyanov

Burmannia unguiculata is described in Averyanov (2005) from limestone grounds in northern Vietnam. Together with its closest relative B. coerulea it is endemic to its type locality. B. unguiculata differs from B. coerulea by its smaller size (5 - 10 cm vs. 10 - 20 cm), lighter colour of  stems, scale leaves and flowers (more blueish in B. coerulea) and a dense scale leaf cover at the stem base. Moreover, B. unguiculata has smaller flowers in comparison to B. coerulea (although the latter also has small flowers compared to other Burmannia sp. in Vietnam), and has caudate sepal lobes (not so in B. coerulea, instead, the sepal margins are involute to some extent). Both species have relatively shallow wings at the floral tube, a characteristic feature to discern Burmannia vs. Gymnosiphon. Thus, the author suspects the two new Burmannia spp. as being transitional to the genus Gymnosiphon.
A more recent study (Xiaojuan et al. 2023) suspects, B. unguiculata might be another Campylosiphon species, based on the similarity to the newly described C. saundersii. However, Xiaojuan et al. (2023), focussed on the revision of the genus Campylosiphon, was not able to conduct investigations specific to this issue.