One of the most confusing groups of plants in the Rubiaceae family would be the Hedyotis-Oldenlandia complex [1-2] which comprises of a large number of generic names with approximately 500 to 600 species [2] of plants. This complex is part of the tribe Spermacoceae.

In 2015, a publication by Neupane proposed a 13-genera system for Asia-Pacific taxa of the Hedyotis-Oldenlandia complex [2]. Subsequently, a publication by Hsu adopted this new system in their 2017 publication that listed 17 species of the Hedyotis-Oldenlandia complex in Taiwan [3]. Nevertheless, in another recent publication from Australia in 2017 by Westaway [4], it noted 20 Oldenlandia and 4 Hedyotis species distributed across the northern half of Australia based on a review done in 1992 but did not adopt the new system by Neupane. In Singapore, there are 13 members in this complex were listed in the 2009 Singapore flora checklist. A species not listed but may be available here based on my encounter in a park in April 2016 is Oldenlandia tenelliflora. It will be of interest to know whether this new system will be adopted in the future revision of this flora checklist.

An example of a common species in this complex that is found in Singapore that will be affected by this new naming system is Oldenlandia biflora. Based on the new system, its name should be Leptopetalum biflorum while the current name Oldenlandia biflora will become one of its synonyms. Oldenlandia biflora looks very similar to Oldenlandia corymbosa, another very common weedy plant here.

To date, the accepted names in the Plant List website has yet to adopt the system proposed by Neupane.

References:

[1] Guo X, Wang RJ, Simmons MP, But PP, Yu J. Phylogeny of the Asian Hedyotis-Oldenlandia complex (Spermacoceae, Rubiaceae): evidence for high levels of polyphyly and the parallel evolution of diplophragmous capsules. Mol Phylogenet Evol 2013;67(1):110-122. | Abstract |

[2] Neupane S, Dessein S, Wikstrom N, Lewis PO, Long C, Bremer B, Motley TJ. The Hedyotis-Oldenlandia complex (Rubiaceae: Spermacoceae) in Asia and the Pacific: Phylogeny revisited with new generic delimitations. Taxon 2015;64(2):299-322. | Read article |

[3] Hsu TC, Chen ZH. Scleromitrion sirayanum (Rubiaceae: Spermacoceae), a new species of the Hedyotis-Oldenlandia complex in Taiwan. Taiwania 2017;62(2):151-156. | Read article |

[4] Westaway JO. Oldenlandia pinifolia (Wall. ex G.Don) Kuntze (Rubiaceae), a new addition to the flora of Australia. Austrobaileya 2017;10(1):93-101. | Read article |