Introduction

Macroptilium gracile (Poepp. ex Benth.) Urb. is distributed in Central and South America, and is an extremely variable species. Ever since Bentham (1837) described its basionym Phaseolus gracilis Poepp. ex Benth., the species has been the subject of controversy. This situation has created confusion among botanists and non-botanists working with this important forage species (Cook et al. 2020).

On the basis of morphological, molecular and biogeographic data (which included revision of vouchers from the herbaria ABH, HERZU, IRBR, K, M, MY, NY, PORT, S, UOJ, VEN and W; acronyms according to Thiers 2021, continuously updated), Berlingeri et al. (2020) concluded that there is enough evidence to separate the Macroptilium gracile species complex into two distinct species: M. gracile and M. campestre (Mart. ex Benth.) Berlingeri, M.B.Crespo & Calles (= Phaseolus scolecocarpus Piper). The former is widely distributed in Central and South America, and exhibits broad morphological variation. For this reason, Berlingeri et al. (2020) described one infraspecific taxon based on the earliest legitimate name at the same rank (i.e. Phaseolus longepedunculatus var. subcoriaceus Benth.) as sanctioned by the International Code of Nomenclature for algae, fungi, and plants (hereinafter referred to as the Code) (Art. 11.4, Turland et al. 2018). This also generated an autonym (i.e., Macroptilium gracile var. gracile) as sanctioned by the Code (Art. 26.1, Turland et al. 2018). Unfortunately, this solution is in conflict with the Code because according to Article 11.6 (Turland et al. 2018) “an autonym is treated as having priority over the name or names of the same date and rank that established it”.

In the present contribution, we discuss nomenclatural issues concerning the Macroptilium gracile species complex and explore ways to overcome shortcomings of the publication Berlingeri et al. (2020). As a result, a new combination is established.

Historical Background

Bentham (1837) described the species Phaseolus longepedunculatus Mart. ex Benth. and three new varieties: a) var. latifolius Benth. nom. nud. (associated with: in sylvis Catingas ad Joazeiro provinciae Bahia, Martius s.n. [M-0174112!]); b) var. angustifolius Benth. nom. nud. (associated with: in pascuis herbidis planitierum provinciae Piauhi, Martius s.n. [M-0174109!, M-01741010! & M-01741011!]); and c) var. subcoriaceus Benth. (type: ad Ribeirao Catinga, Pohl s.n. [K-000189691!]). The varieties latifolius and angustifolius do not have any description or diagnosis, and neither was accompanied by reference to any previous one; therefore, they were not validly published and must be considered nomina nuda. However, the varietal name subcoriaceus was validly published because it was accompanied by a description (Art. 38.1, Turland et al. 2018), and it is a legitimate name since it was established in accordance with the Code rules (Art. 6.5, Turland et al. 2018). Furthermore, Phaseolus longepedunculatus vars latifolius and angustifolius do not appear in the database of the International Plant Name Index (IPNI — https://www.ipni.org/), whereas var. subcoriaceus does. Additionally, the detailed Latin description placed just below that name in the protologue matches the characteristics of the voucher Pohl s.n. deposited at the Royal Botanic Gardens (K-000189691!); which is original material used by Bentham (1837) and was designated as lectotype of the taxon in question by Berlingeri et al. (2020).

Nomenclatural Treatment

Berlingeri et al. (2020) have already clarified the status of the so-called Macroptilium gracile species complex; therefore, we will only address the nomenclatural issue regarding the correct name of the infraspecific taxa of M. gracile established by Berlingeri et al. (2020).

Bentham (1837) validly published the name Phaseolus longepedunculatus var. subcoriaceus, which automatically established the corresponding autonym (i.e., P. longepedunculatus var. longepedunculatus). Additionally, Bentham (1837) published two new varieties (i.e., var. latifolius and var. angustifolius) but these are considered nomina nuda because they do not have any description or diagnosis, and were not accompanied by reference to any previous one (Art. 38; Turland et al. 2018).

Piper (1926) was the first to consider Phaseolus gracilis and P. longepedunculatus as extreme forms of a single species, based on the existence of abundant intermediate individuals. Consequently, he selected P. gracilis as the accepted name and synonymised P. longepedunculatus. After Piper’s (1926) treatment, some authors considered Macroptilium gracile (≡ Phaseolus gracilis) and M. longepedunculatum (Mart. ex Benth.) Urb. (≡ Phaseolus longepedunculatus) as distinct species (e.g., Urban 1928a; Verdcourt 1970; Maréchal et al. 1978), while other authors (e.g., Barbosa-Fevereiro 1987; Espert et al. 2007) agreed with Piper (1926).

After using multiple lines of evidence, Berlingeri et al. (2020) agreed with Piper (1926) that Macroptilium gracile and M. longepedunculatum are conspecific; however, they concluded that there was enough evidence to maintain two varieties. Unfortunately, they selected the infraspecific epithet subcoriaceum, in conflict with Article 11.6 (Turland et al. 2018). According to the Article 11.6 (Turland et al. 2018) “an autonym is treated as having priority over the name or names of the same date and rank that established it”; therefore; the correct infraspecific epithet of the taxon in question should be longepedunculatum.

Macroptilium gracile (Poepp. ex Benth.) Urb., Symb. Antill. 9 (4): 457 (Urban 1928a) ≡ Phaseolus gracilis Poepp. ex Benth., Comm. Legum. Gen.: 77 (Bentham 1837). Lectotype (designated as “holotype” by Barbosa-Fevereiro 1987 and corrected to lectotype by Berlingeri et al. 2020): Cuba, Poeppig s.n. (W0045836!).

Macroptilium gracile var. gracile

= Phaseolus longepedunculatus var. angustifolius Benth., Comm. Legum. Gen.: 77 (Bentham 1837), nom. nud. Associated with: Brasil, In pascuis herbidis planitierum provinciae Piauhiensis, Maio, Martius s.n. [M0174109 (photograph!); M0174110 (photograph!); M0174111 (photograph!)].

= Phaseolus savannarum Britton & P.Wilson, Mem. Torrey Bot. Club 16 (2): 70 – 71 (in Britton 1920). Holotype: Cuba, Pinar del Rio, Herradura, Earle 632 [NY (photograph!)].

= Phaseolus longepedunculatus var. linearifoliolatus Hassl., Candollea 1: 453 (Hassler 1923). Syntypes: Guatemala, Türckheim 3573 (Herb. Delessert, G — not seen); Costa Rica, Shannon 6022 (G — not seen).

= Phaseolus longepedunculatus f. boliviensis Hassl., Candollea 1: 453 (Hassler 1923). Holotype: Bolivia, Santa Cruz, Steinbach 2046 (possibly at BAF, BREM, MVM; not seen).

= Phaseolus unilobatus Pittier, Bol. Técn. Minist. Agric. 5: 55 (Pittier 1944). Holotype: Venezuela, Monagas, Maturín, Pittier 14352 (VEN48769!).

Macroptilium gracile var. longepedunculatum (Mart. ex Benth.) Berlingeri, M.B.Crespo & Calles comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77234368-1

Phaseolus longepedunculatus Mart. ex Benth., Comm. Legum. Gen.: 77 (Bentham 1837) ≡ Macroptilium longepedunculatum (Mart. ex Benth.) Urb., Symb. Antill. 9 (4): 457 (Urban 1928a). Lectotype (designated here): Brazil. Ad Ribeirão Catinga, Pohl s.n. (K-000189691!); isolectotypes: W-0045835 (photograph!), NY (not seen).

= Phaseolus longepedunculatus var. latifolius Benth., Comm. Legum. Gen.: 77 (Bentham 1837), nom. nud. Associated with: Brazil. In sylvis Catingas ad Joazeiro provinciae Bahia, Martius s.n. [M-0174112 (photograph)!].

= Macroptilium gracile var. subcoriaceum (Benth.) Berlingeri, M.B.Crespo & Calles, Bot. J. Linn. Soc. 194 (1): 132 (2020), nom. superfl. [Art. 52.4] ≡ Phaseolus longepedunculatus var. subcoriaceus Benth., Comm. Legum. Gen.: 77 (Bentham 1837). Lectotype (designated by Berlingeri et al. 2020: 132): Brazil. Ad Ribeirão Catinga, Pohl s.n. (K-000189691!); isolectotypes: W-0045835 (photograph!), NY (not seen).

= Phaseolus longepedunculatus f. typicus Hassl., Candollea 1: 452 (Hassler 1923), nom. invalid. pro parte (excl. ‘Colombia: Santa Marta, Smith 287’).

= Phaseolus longepedunculatus f. glabratus Hassl., Candollea 1: 452 (Hassler 1923). Lectotype (designated by Torres Colín 2006): Paraguay. Paraguay, Hassler 6197 (K!).

= Macroptilium domingense Urb., Ark. Bot. 22A (8): 51 – 52 (Urban 1928b). Holotype: Haiti. Haiti, Ekman H-9401 [S-R-9483 (photograph)!].

= Phaseolus diversifolius Pittier, Bol. Técn. Minist. Agric. 5: 56 (Pittier1944), nom. illegit., non Pers., Syn. Pl. 2 (2): 296 (Persoon 1807). Holotype: Venezuela. Anzoátegui, Guaraguara, near Santamé, Pittier 14302 (VEN-198640!).

Nomenclatural Note

The name Phaseolus longepedunculatus was published by Bentham (1837) and he made reference to three specimens (i.e., two collected by Carl von Martius and another collected by Johann Pohl), which should be treated as syntypes (Art. 9.6, Turland et al. 2018). We have designated Pohl’s specimen deposited at K (K-000189691) as lectotype of Macroptilium gracile var. longepedunculatum based on Article 9.12 (Turland et al. 2018) and because it is the one fixing the application of Bentham’s description.