(3135) Proposal to conserve the name <i>Ammannia prostrata</i> ( <i>Nesaea prostrata</i> ) against <i>A. debilis</i> ( <i>Lythraceae</i> )

(3135) Ammannia prostrata Buch.-Ham. ex Dillwyn, Rev. Hortus Malab.: 47. 2 Apr 1839 [Angiosp.: Lythr.], nom. cons. prop. Typus: [icon] “Beli-tsjira” in Rheede, Hort. Malab. 9: t. 84. 1689. (=) Ammannia debilis Aiton, Hort. Kew. 1: 163. 7 Aug–1 Oct 1789, nom. rej. prop. Lectotypus (see Prasanth & Sardesai in Rheedea 35: 249. 2025): [United Kingdom, London, Richmond upon Thames,] Kew, Royal Botanical Garden, 1778 (BM barcode BM001122163!). The taxonomic circumscriptions and generic boundaries of Ammannia L. (Sp. Pl.: 119. 1753) and Nesaea Comm. ex Kunth (in Humboldt & al., Nov. Gen. Sp. 6, ed. fol.: 151. 1823), nom. cons. have long been debated, as the two genera are distinguished based on irregular dehiscence (Ammannia) and initial circumscissile dehiscence (Nesaea) (Graham in Kubitzki, Fam. Gen Vasc. Pl. 9: 236. 2007). Ammannia debilis Aiton (Hort. Kew. 1: 163. 1789) was described based on a specimen cultivated along the Thames River, London, with “East Indies” stated as the native range, with the plants having been introduced by Sir Joseph Banks in 1778. A century later, Clarke (in Hooker, Fl. Brit. India 2: 570. 1879) published the name Ammannia lanceolata B. Heyne ex C.B. Clarke. Thereafter, Koehne (in Bot. Jahrb. Syst. 3: 325. 1882) transferred A. lanceolata to Nesaea as N. lanceolata (B. Heyne ex C.B. Clarke) Koehne, based on initial circumscissile dehiscence capsule and persistent style. This treatment was maintained in the monograph of Lythraceae by Koehne (in Engler, Pflanzenr. IV. 216 (Heft. 17): 226. 1903), and followed by later Indian revisions and floras (Blatter & Hallberg in J. Bombay Nat. Hist. Soc. 26: 210–218. 1918; Gamble, Fl. Madras 1: 506–515. 1919; Mathew, Fl. Tamil Nadu Carn. 3: 605–610. 1983; Saxena & Brahamam, Fl. Orissa 2: 705–724. 1995; Saldhana, Fl. Karnataka 2: 14 1996; Pullaiah & Chennaiah, Fl. Andhra Pradesh 1: 391–398. 1997; Mathew & al., Fl. Pl. India: Ann. Checkl. (Dicot.) 1: 557–562. 2020). In the meantime, Dillwyn (Rev. Hortus Malab.: 47. 1839) validly published the name Ammannia prostrata Buch.-Ham. ex Dillwyn based on Van Rheede's plate “Beli-tsjira” (Hort. Malab. 9: t. 84. 1689), on which it was effectively typified by Mabberley (in Taxon 26: 531, 533. 1977). Suresh (in Nicolson & al., Interpr. Van Rheede's Hort. Malab.: 168. 1988) transferred A. prostrata to Nesaea as N. prostrata (Buch.-Ham. ex Dillwyn) Suresh, asserting the priority of the epithet ‘prostrata’ over ‘lanceolata’, and treated N. lanceolata as a heterotypic synonym. Subsequently, several authors followed Suresh's treatment in their work (Verdcourt in Dassanayake & al., Rev. Handb. Fl. Ceylon 9: 202–228. 1995; Cook, Aquat. Wetl. Pl. India: 252. 1996; Almeida, Fl. Maharashtra 2: 287. 1998; Sunil & Sivadasan, Fl. Alappuzha: 301. 2009; Chowdhury & al. in N. Bengal Univ. J. Pl. Sci. 9: 73. 2015). However, Graham & al. (in Bot. J. Linn. Soc. 166: 1–19. 2011) concluded that the genera Hionanthera and Nesaea are congeneric with Ammannia, based on morphological, karyological, and molecular evidence and recovered a monophyletic lineage. Consequently, the transfer of names from Nesaea and Hionanthera to Ammannia was accomplished by Graham & Gandhi (in Harvard Pap. Bot. 18: 80. 2013), in which the name A. prostrata was accepted, considering its priority over A. lanceolata. Also, a specimen (“Wallich Cat. No. 2106”) at K herbarium was designated as lectotype for the name A. lanceolata. However, a specimen at BM (Thwaites 2796: barcode BM000944558) had already been effectively designated as lectotype by Panigrahi (in Bull. Bot. Surv. India 18: 186. 1979), which makes the first- and second-step lectotype (K barcode K001115171) designated by Graham & Gandhi (l.c.) and Prasanth & Sardesai (in Phytotaxa 660: 246. 2024), respectively, superfluous. Following the work of Graham & Gandhi (l.c.), the name A. prostrata has been recognized as an accepted name in recently published literature and online databases (Britto, Fl. Centr. N. Tamil Nadu 2: 1233–1249. 2019; Plants of the World Online [POWO, 2025]; World Flora Online [WFO, 2025]). In the recent taxonomic study of the genus Ammannia in India, based on morphological characters like oblong to linear-lanceolate leaves with attenuate base, axillary cyme, hypanthium 1.5–2 mm long, hirsute calyx lobes, and petals up to 1 mm long, it was concluded that A. debilis is conspecific with A. prostrata (Prasanth & Sardesai in Rheedea 35: 249. 2025). Although the name A. debilis has nomenclatural priority over A. prostrata, the name has been inconsistently applied, as a synonym of A. baccifera L. (l.c.: 120) by Clarke (l.c.: 569), and as A. multiflora Roxb. (Fl. Ind. 1: 447. 1820) tentatively by Koehne (l.c. 1903: 48). Subsequently, Miquel (Fl. Ned. Ind. 1(1): 615. 1856) proposed the combination Ditheca debilis (Aiton) Miq. based on Zollinger's collection from Java (Moritzi, Syst. Verz.: 12. 1846), without seeing the specimen. Recently, De Wilde & Duyfies (in Blumea 59: 13. 2014), in a study of Malesian species, recognized A. debilis as a distinct taxon from South India, but the study did not include consideration of other related taxa from that region. They also identified a specimen from the Banks Herbarium, now at BM (barcode BM001122163), annotated “Ammannia debilis MS”, allegedly in Banks's handwriting, and “Hort. Kew 1778”, that has been designated by Prasanth & Sardesai (in Rheedea 35: 249. 2025) as lectotype. As mentioned above, although Ammannia debilis has nomenclatural priority, the name has long been misapplied and has not been consistently used. The name A. lanceolata was used for a long time following Koehne's (l.c. 1882) work, but Suresh (l.c.) adopted Nesaea prostrata because its basionym A. prostrata has priority over A. lanceolata. Subsequently, following Graham & Gandhi (l.c.), usage of the name A. prostrata has become standardized in recent literature and databases. Therefore, to preserve nomenclatural stability, we propose to conserve the name A. prostrata over A. debilis. This will help prevent unwanted changes that could impact taxonomic and floristic studies. We thank John McNeill and Mayur Nandikar for the valuable discussion and advice. We also acknowledge the curators of BM and K for granting permission and extending support to consult the Lythraceae specimens during a visit, and IAPT for supporting the research trip to the U.K. herbaria.