Millettia penduliformis Gagnepain (1916b: 200)

Song, Zhu-Qiu, Li, Shi-Jin, Vu, Quang Nam & Khang, Nguyen Sinh, 2022, Taxonomic notes on the genus Millettia (Fabaceae: Millettieae) in Vietnam, Phytotaxa 571 (2), pp. 169-185 : 175-177

8. Millettia penduliformis Gagnepain (1916b: 200) .

Type: — LAOS. plateau d’Attopeu , 500 m, March 1877, F. J. Harmand 1408 (lectotype: P02141845 image!, designated by Lôc & Vidal 2001: 146; isolectotypes: P02141846 image!, P02141847 image!) ; VIETNAM. Pho-qua, dans la prov. de Bien-hoa, March 1877, L. Pierre s.n. (remaining syntype: P02753872 image!) .

Millettia penduliformis was originally described on the basis of two flowering collections, i.e. F. J. Harmand 1408 from Laos ( Fig. 4A ) and L. Pierre s.n. ( Fig. 4B ) from Vietnam ( Gagnepain 1916b). In the protologue, the author considered that the species can be distinguished from M. pendula Benth. ex Baker (1876: 105) by its larger and acute leaflets, caducous stipules, elongated inflorescences, a standard petal without basal callosities and auricles, and a single ovule. Millettia pendula is a superfluous and illegitimate name because M. leucantha Kurz (1873: 68) was cited as its synonym when published (Art. 52.2 of ICN, Turland et al. 2018). Recently, M. leucantha was transferred to the genus Imbralyx with unique characters within Millettieae , which is quite different from the genus Millettia (Song 2021) .

Our examination of literature and specimens showed that M. penduliformis may be conspecific with M. pachyloba , because both share very similar morphological features. But it may be reasonable to conduct more investigations before this is formalised. In Flore générale de l’Indo-Chine ( Gagnepain 1916a), M. pachyloba was placed in the section IV with diadelphous stamens, and M. penduliformis was placed in section VI with monadelphous stamens. However, Mattapha (2020) clearly described M. penduliformis with diadelphous stamens. The shape of the pods and number of ovules per ovary were also used to identify M. pachyloba and M. penduliformis ( Mattapha 2020: 3–6 vs. 1–2 ovules, cylindrical vs. subglobose pods; Lôc & Vidal 2001: 4–6 vs. 1 (–2) ovules, ellipsoid or subcylindrical vs. elliptical pods). But Hô (1999) pointed out that M. penduliformis has 3-seeded pods. In fact, the pod of M. pachyloba also bears subglobose pods with one seed, as shown in its syntype ( Fig. 4D ). Many authors described M. pachyloba with 1–4 seeds per fruit ( Wei 1994, Li et al. 2001, Sun 2006, Wu et al. 2006, Wei & Pedley 2010). Mattapha (2020) also provided several other differences between M. pachyloba and M. penduliformis in their descriptions, such as shape of the leaflet apex (obtuse, sometimes with apiculate tip ca 2 mm long vs. acute), number of lateral veins (10–15 vs. 13–24 pairs), and length of the stipels (5–9 vs. ca 3 mm). But these features are inconsistent with those reported in Lôc & Vidal (2001), who indicated no significant differences in these aspects (abruptly acuminate, mucronate or obtuse vs. abruptly and shortly acuminate, mucronate or obtuse, 9–15 vs. 10–17 pairs, and 3 vs. 3 mm). Our examination of the type specimens ( Fig. 4C–D of M. pachyloba , Fig. 4A–B of M. penduliformis ) also suggested no significant differences between them (acuminate to obtuse vs. acuminate or shortly acuminate, 13–20 vs. 11–17 pairs, and 1.7–2.6 vs. 1.6–2.3 mm). Until to now, we just observed that they are markedly different in the size of the flowers (14–17 mm long for M. pachyloba vs. 7–10 mm long for M. penduliformis ). We are not sure whether it is resulted from the unopened flowers of specimens of the latter species, as the mature material is not available to us.

In addition, some studies indicated that the two species have a standard petal with two basal callosities ( Dunn 1912, Lôc & Vidal 2001, Mattapha 2020), but this is inconsistent with the descriptions by other authors (e.g. Gagnepain 1916a, Sun 2006, Wei & Pedley 2010) who described them with no callosities. Based on living material, we also did not observe basal callosities for M. pachyloba (living material of M. penduliformis was not available to us). Morphologically, M. penduliformis and M. pachyloba are very similar to M. rubiginosa Wight & Arnott (1834: 263) ; they share a unique combination of characters, including woody climbers, stipellate leaflets with non-silvery lower surfaces, distinct brachyblasts, a standard with sericeous hairs outside, wings with two patches of golden hairs, diadelphous stamens, and tomentose pods. But the two former species have rather inflated (vs. compressed) mature pods and a different distribution. M. penduliformis and M. pachyloba are distributed in China, Thailand, Laos, Cambodia and Vietnam, while M. rubiginosa is endmic to South India.

Figures

FIGURE 4. Millettia penduliformis Gagnep. (A–B) and M. pachyloba Drake (C–D). A. isolectotype of M. penduliformis (F. J. Harmand 1408, P02141847, https://science.mnhn.fr/institution/mnhn/collection/p/item/p02141847); B. syntype of M. penduliformis (L. Pierre s.n., P02753872, https://science.mnhn.fr/institution/mnhn/collection/p/item/p02753872); C. isolectotype of M. pachyloba (B. Balansa 2306, K000848750, http://specimens.kew.org/herbarium/K000848750); D. syntype of M. pachyloba (B. Balansa 2308, P02753729, https://science.mnhn.fr/institution/mnhn/collection/p/item/p02753729). A, B & D ©copyright of Muséum national d’Histoire naturelle. C ©copyright of the Board of Trustees of the Royal Botanic Gardens, Kew.