Apios carnea (Wallich, 1830) Bentham ex Baker, 1876

Egan, Ashley N. & Pan, Bo, 2015, Pueraria stracheyi, a new synonym to Apios carnea (Fabaceae), Phytotaxa 218 (2), pp. 147-155 : 150-151

Similarities to Apios carnea

A key feature that stands out on the holotype of Pueraria stracheyi ( Fig. 1 ) is the distinct curvature of the flowers in bud. Author A.N. Egan first saw flower buds with a similar shape whilst collecting legumes in Thailand in 2013 where she collected Apios carnea (Wallich 1830: 50) Bentham ex Baker (1876: 188) . The same distinct curvature was observed by author B. Pan during his collection of Apios carnea in Menghai County, Yunnan, China, a photograph of which is shown in Figure 3 . Upon further investigation, both authors concluded that P. stracheyi is actually an Apios . In the same volume where he described P. stracheyi, Baker also described Apios carnea , therein attributed to Bentham. Apios Fabricius (1759: 176) is a genus of about eight species. Like a number of other East Asian genera, Apios has a disjunct distribution with six species in East Asia and two species endemic to North America (Sa and Gilbert 2010a). Apios is easily distinguished by its large, usually strongly curved keel with highly reduced wing petals relative to the standard and keel petals. It also has a curved staminal column with a circular style. These features coupled with leaves having (3–)5–9 leaflets place the genus as somewhat uncharacteristic within Phaseoleae . Phylogenetically, Apios is suggested to be the sister to remaining phaseoloid legumes (Egan et al, unpublished data).

Apios carnea is distinct from its Asian congeners by having red, reddish purple, or orange flowers coupled with leaflets longer than 5 cm (Sa and Gilbert 2010b). In addition, it is the only Asian species with inflorescences commonly longer than 30 cm (B. Pan, personal observations; Sa and Gilbert, 2010b). Apios carnea shares similar flower color with its American congeners, A. americana Medikus (1787: 355) and A. priceana B.L. Robinson (1898: 451) , but is differentiated by its longer calyx lobes: the top two fused calyx lobes are 4–5 mm long in A. carnea whereas the American species exhibit a top calyx lobe that is almost truncate, with a length of less that 1 mm (Woods 2005). The longer calyx lobes are markedly evident in Figure 3 . Furthermore, A. carnea has a long, lax inflorescence that often exceeds 30 cm whilst those of A. priceana and A. americana are densely flowered with inflorescence lengths usually less than 16 cm long.

The holotype of Pueraria stracheyi ( Fig. 1 ) fits well within the description of Apios carnea . Although the flowers on the holotype are not quite open, the largest shows the distinctly curved keel petal ( Fig. 1 ). Pueraria stracheyi is described as being a scandent herb with red flowers that was found flowering in August (Strachey 1906), a description that fits perfectly with that of Apios carnea (Sa and Gilbert 2010b) . Pueraria stracheyi shares a number of leaf features with Apios carnea , including obovate-oblong leaflets with a caudate apex and darker green coloration above with a paler coloration below ( Table 1). In addition, flower features also unite the two: P. stracheyi has a flower length exceeding 2 cm, pedicel length of 5 mm, a calyx of ~ 1 cm with distinct calyx lobes, the upper two lobes entirely connate, 4–5 mm long, the shorter, lateral lobes deltoid, 2–3 mm, and the lower lobe lanceolate, 4–6 mm long. Lastly, according to collection records collated by the Global Biodiversity Information Facility (www.gbif.org), Apios carnea is distributed throughout southeast Asia and is prevalent across the Himalayas. The collection that was later described as Pueraria stracheyi fits easily into the range described for Apios carnea ( Fig. 4 ). The conglomeration of matching features leaves no doubt that P. stracheyi is actually Apios carnea . We here designate Pueraria stracheyi as a synonym of Apios carnea . A key to species is also presented.

Figures

FIGURE 1. Holotype of Pueraria stracheyi Baker collected by Strachey & J.E. Winterbottom s.n. (K). Photographed with permission by Ashley N. Egan while on loan to the U.S. National Herbarium (US).

FIGURE 3. Flowers and buds of Apios carnea. Note the caudate leaf apex in the upper left hand corner. Locality: Hesong, Menghai County, Xishuangbanna, Yunnan, China. Photographed by Bo Pan.

FIGURE 4. Distribution of Apios carnea in Asia (yellow dots); probable locality for Pueraria stracheyi (red dot). Data collected from the Global Biodiversity Information Facility.