The specimens of Wenchengia from Vietnam were discovered during preparatory work for the Flora of Thailand Lamiaceae account, and examination of specimens of Scutellaria L. and indetermined Lamiaceae housed in P. The description below is based on the Vietnam material and the detailed observations of Li et al. (2014), Li et al. (2012), Cantino and Abu-Asab (1993), material in MO from Hainan, and on an isotype of Wenchengia alternifolia also identified in the herbarium in Paris, which was previously determined as Scutellaria sp. The text in parentheses in the description below identifies the slight morphological differences between the Vietnam material and that from Hainan.

It is perhaps not surprising that Wenchengia is not endemic to Hainan. Francisco-Ortega et al. (2010), reporting seven endemic genera, anticipated that many species endemic to Hainan would lose their endemic status once the floras of Vietnam and South China were better studied, and Zhu et al. (2003) report a similarity coefficient at generic level of 90.8% between the flora of Vietnam and Hainan. What is more surprising is that the three collections all predate the collection of the type and paratype from Hainan, but no record of Wenchengia in Vietnam has been documented (Phuong 2000). The Clemens specimens were collected in 1927. The P.A. Eberhardt collection has no collection date, but he is known to have collected in Vietnam between 1906 and 1920 (Lecomte 1944).

This discovery of Wenchengia in Vietnam suggests that the Hainan populations are a relict of a once, and perhaps still, wider distribution. Wenchengia lies at the base of a clade including Holmlskioldia Retz. which is in turn is sister to Tinnea Kotschy & Peyr., Renschia Vatke and Scutellaria. Whereas Scutellaria is subcosmopolitan, Tinnea is African, Renschia endemic to N. Somalia, and Holmskolidia is found from the Himalaya to Myanmar (Cantino 1992, Harley et al. 2004).

The Vietnamese populations are morphologically similar to those from Hainan, the main differences being vegetative. The character variation is similar to the sorts of infraspecific variation seen in species of Scutellaria. The populations in Hainan are small, and given the few collections in Vietnam, any populations there are likely also to be small. A level of genetic drift between the populations might be expected, but genetic study of the populations is required to further investigate this. It is not known whether the Vietnamese populations are still extant, and the exact localities of the collections are unclear. There has been a lot of recent development in the tourist industry in the Ba Na Hills, Da Nang Province, which has had a tourist resort since 1919 and now hosts the worlds longest cable car system (Anon. 2016). The Eberhardt locality, 'Hoi-Mit' in Thua Than-Hue Province has not been traced. It is possible that the locality is now in, or close to, the Bach Ma National Park, close to Ba Na, from where recently a new species of Callicarpa, Callicarpa bachmaensis Soejima & Tagane, was discovered growing in a similar habitat to Wenchengia (Soejima et al. 2016). Efforts to search for extant populations could focus in Bach Ma in addition to the Ba Na Hills, in rocky river or path banks within forest.