Cheilocostus was split out of Costus in 2006 based on the cladistic analysis of Dr. Chelsea Specht. She compared the phylogenetic relationships between species and concluded that the Asian Costus were in a separate clade closer to the genus Tapeinochilos and should be classified as a separate genus. This was supported by a number of morphological characteristics such as their tendency to branch the stems and pungent bracts. Cheilocostus species are further distinguished from Costus by having seasonally deciduous leaves (per Specht description) and a bicarinate (two keeled) bracteole as in Chamaecostus and only rarely in Costus. The stigma is a modified cup shape with a small rounded appendage, unlike the two-lobed appendage in Costus.
And of course... now that the name Cheilocostus has finally sunk in, the taxonomists have discovered an earlier name that according to the rules must replace Cheilocostus. In 2013 an article was published in Phytotaxa explaining that the type species selected for the new genus (C. speciosus) was known by an earlier name (Banksea speciosa) which in turn was based on an even earlier genus name, Hellenia, such that the new genus name of Cheilocostus must now be changed to Hellenia. If you want to read the entire convoluted story of this, CLICK HERE. Meanwhile, I am keeping these species listings under Cheilocostus until I am sure the dust is all settled and there is consensus among the taxonomists.
As recently as January 2021, the respected botanist Axel Poulsen co-authored a paper in the Edinburgh Journal of Botany (https://doi.org/10.24823/EJB.2021.337) regarding chromosome counts of Asian Costaceae in which the following statement:
The name Cheilocostus is superfluous because an older name is available: Hellenia Retz. This name, however, is confusing, because Hellenia Willd. nom. illeg. has been used widely for species now placed in Alpinia Roxb. in Zingiberaceae, the sister family to Costaceae. A proposal to conserve the name Cheilocostus, or at least move away from the confusing Hellenia, has therefore been initiated (Leong-Skornickova & Sida, 2016). Because a decision has yet to be made, we adhere in this publication to the use of the generic name Cheilocostus so as not to confuse the situation further or to establish the use of Hellenia.
Cheilocostus is very much in need of further study by taxonomists as there are only a few accepted species, two of which are quite widespread and variable (C. speciosus and C. globosus) and are treated as complexes that may eventually be divided into separate species or subspecies. Further discussion of this issue will be found by following the links below.
SHOWN IN PHOTO: Cheilocostus globosus