Neltuma Raf., Sylva Tellur.: 119. 1838.

Bruneau, Anne, de Queiroz, Luciano Paganucci, Ringelberg, Jens J., Borges, Leonardo M., Bortoluzzi, Roseli Lopes da Costa, Brown, Gillian K., Cardoso, Domingos B. O. S., Clark, Ruth P., Conceicao, Adilva de Souza, Cota, Matheus Martins Teixeira, Demeulenaere, Else, de Stefano, Rodrigo Duno, Ebinger, John E., Ferm, Julia, Fonseca-Cortes, Andres, Gagnon, Edeline, Grether, Rosaura, Guerra, Ethiene, Haston, Elspeth, Herendeen, Patrick S., Hernandez, Hector M., Hopkins, Helen C. F., Huamantupa-Chuquimaco, Isau, Hughes, Colin E., Ickert-Bond, Stefanie M., Iganci, Joao, Koenen, Erik J. M., Lewis, Gwilym P., de Lima, Haroldo Cavalcante, de Lima, Alexandre Gibau, Luckow, Melissa, Marazzi, Brigitte, Maslin, Bruce R., Morales, Matias, Morim, Marli Pires, Murphy, Daniel J., O'Donnell, Shawn A., Oliveira, Filipe Gomes, Oliveira, Ana Carla da Silva, Rando, Juliana Gastaldello, Ribeiro, Petala Gomes, Ribeiro, Carolina Lima, Santos, Felipe da Silva, Seigler, David S., da Silva, Guilherme Sousa, Simon, Marcelo F., Soares, Marcos Vinicius Batista & Terra, Vanessa, 2024, Advances in Legume Systematics 14. Classification of Caesalpinioideae. Part 2: Higher-level classification, PhytoKeys 240, pp. 1-552 : 1

Neltuma Raf., Sylva Tellur.: 119. 1838.

Figs 138 , 139 , 142

Prosopis sect. Algarobia DC., Prodr. [A.P. de Candolle] 2: 446. 1825. Type: Prosopis algarobilla Griseb. [= Neltuma affinis (Spreng.) C.E. Hughes & G.P. Lewis]

Mitostax Raf., Sylva Tellur.: 120. 1838. Type: Mitostax pallida (Humb. & Bonpl. ex Willd.) Raf. [≡ Acacia pallida Humb. & Bonpl. ex Willd. (≡ Neltuma pallida (Humb. & Bonpl. ex Willd.) C.E. Hughes & G.P. Lewis)]

Algarobia (DC.) Benth., Pl. Hartw.: 13. 1839. Type: Algarobia dulcis (Kunth) Benth. [= Neltuma laevigata (Humb. & Bonpl. ex Willd.) Britton & Rose]

Prosopis sect. Monilicarpa Ruiz Leal ex Burkart, J. Arnold Arbor. 57(3): 230. 1976. Type: Prosopis argentina Burkart [≡ Neltuma argentina (Burkart) C.E. Hughes & G.P. Lewis]

Type.

Neltuma juliflora (Sw.) Raf. [≡ Mimosa juliflora Sw.]

Description.

Spiny, erect to prostrate subshrubs, shrubs and small trees, (0.1) 4-10 (20) m tall, usually with a short trunk to 40-60 (>100) cm diameter (Fig. 138D, E ), branching lax, crown spreading, rounded or flat-topped, twigs flexuous, often arched downwards, glabrous, green or reddish, armed with uninodal axillary, solitary or paired, straight, strong, cylindrical, subulate thorns (Fig. 138I ), these not necessarily at all nodes, sometimes thicker than subtending twig, or with spinescent rigid straight cylindrical branchlets (Fig. 138F ); brachyblasts present (sometimes obscure), congested, blackish, or absent. Stipules small, often obscure. Leaves bipinnate, an obscure gland between first pair of pinnae; pinnae 1-3 (8) pairs; leaflets (1) 2-30 (50) pairs, opposite, palmately pinnativeined or almost without veins, or sometimes aphyllous or subaphyllous. Inflorescences axillary, solitary or fascicled, spiciform racemes (Figs 138F, I , 139D-G ). Flowers white, yellow, greenish-yellow or occasionally red (Figs 138F, I , 139D-F ), often perfumed, sometimes functionally staminate flowers proximally; calyx short, valvate; petals 5, valvate, almost free; stamens 10, free, anthers with a minute caducous incurved claviform gland on the connective; pollen in tricolporate monads, exine smooth, perforated, columellae present; ovary sessile or stipitate, stigma porate. Fruits linear moniliform or compressed turgid (Fig. 139G ), straw-yellow, sometimes tinged reddish-maroon or black, indehiscent, glabrous, mostly straight to sub-falcate, S- or C-shaped or annular with 1-3 very lax open spirals but never tightly coiled, margins often thickened and undulate, valves striate, corrugate or smooth, exocarp crustaceous, mesocarp thin or more usually thick and pulpy, mealy or spongy, dry, usually sweet, endocarp hard and bony or coriaceous, segmented in longitudinal or transverse subquadrate closed seed chambers. Seeds brown, compressed ovate, pleurogram present, not closed, testa hard.

Chromosome number.

2 n = 26 or 28 ( Goldblatt 1981b; Bukhari 1997); polyploidy reported in N. juliflora , 2 n = 52 ( Hunziker et al. 1975; Bukhari 1997).

Included species and geographic distribution.

Probably around 30 species. Widespread across seasonally dry tropical and arid regions of the Americas with a Neltuma pseudo -amphitropical bicentric pattern of greatest species diversity in the Mexican-Texan and Argentinian-Chilean-Paraguayan regions, especially diverse and abundant in the Chaco, with an outlying disjunct occurrence of Neltuma ruscifolia (Griseb.) C.E. Hughes & G.P. Lewis of questionable nativity in the Caatinga in north-east Brazil, also extending into warm and some colder temperate areas in Texas and Nevada in the north and Patagonia in the south, where N. denudans Benth. reaches 48°S (Fig. 142 ).

Ecology.

Dominant across large tracts of the Gran Chaco in mixed sub-xerophyllous woodland, also in Monte vegetation, open desert forests in dry quebradas (Fig. 138D ) along seasonal rivers, in Stipa -dominated pampas and semi-desert shrub steppe with hot summers and cold winters in Patagonia as far as 48°S, some species capable of surviving extreme drought; spanning a wide range of substrates and edaphic conditions including stony and sandy mesas, coastal and inland sand dunes and deep black seasonally inundated, sometimes saline, clay vertisols (Fig. 138E ) ( Simpson 1977). The indehiscent cylindrical fruits with a somewhat sugary, thickened, fibrous mesocarp, and an endocarp that is segmented and either thin or, more frequently, somewhat hardened into one-seeded coriaceous or bony seed chambers, and seeds with a hard seed coat and a pleurogram, are eagerly consumed by herbivores, including all kinds of livestock, facilitating effective endozoochorous seed dispersal. This has promoted dispersal and establishment of a subset of species as troublesome invasive weeds, both within their native ranges and where introduced. Neltuma juliflora (Sw.) Raf. is one of the most pernicious plant invaders on the planet ( Shackleton et al. 2014; Ayanu et al. 2015; Kleinjan et al. 2021), with many diverse impacts including enhanced malarial transmission due to habitat changes ( Muller et al. 2017).

Etymology.

Possibly derived from the common name Mulla Thumma in the Dravidian language Teluga in the Indian states of Andhra Pradesh and Telangana, where N. juliflora is introduced.

Human uses.

The wood generally hard, dense, durable and flexible, and widely used for fence posts, parquet flooring, barrels, firewood and charcoal and the dependable provision of large quantities of protein- and sugar-rich, non-toxic, highly palatable and nutritious fruits ( Pasiecznik et al. 2001).

Notes.

Neltuma is one of three genera segregated from Prosopis s.l. ( Hughes et al. 2022b) and corresponds to Burkart’s sections Monilicarpa + Algarobia of Prosopis s.l., characterised by armature in the form of solitary or paired axillary thorns (Fig. 138I ). Hybridisation is apparently common among the subset of species of Neltuma forming the so-called Mezquite subclade ( Hunziker et al. 1986; Castillo et al. 2021).

Thirteen species of ' Prosopis ' have been described since the publication of Burkart’s (1976) monograph, all of which can be confidently placed in Neltuma although some of these new species may be no more than regional variants of the widespread and taxonomically difficult N. pallida / N. juliflora species complex.

Taxonomic references.

Burkart (1976); Hughes et al. (2022b); Johnston (1962); Palacios (2006).

Figures

Figure 138. Habit and armature of the genera of the Neltuma clade A shrub of Xerocladia viridiramis Taub. in the Namib desert, Namibia B small tree of Strombocarpa tamarugo (Phil.) C. E Hughes & G. P. Lewis, on the Pampa del Tamarugal in the Atacama desert, northern Chile C shrubby treelet of Strombocarpa ferox (Griseb.) C. E. Hughes & G. P. Lewis in seasonally dry tropical scrubland in southern Bolivia D small tree of Neltuma kuntzei (Harms ex C. E. O. Kuntze) C. E. Hughes & G. P. Lewis in seasonally dry tropical forest in southern Bolivia E small tree of Neltuma juliflora (Sw.) Raf. in seasonally dry tropical scrubland on deep black vertisol soil in central Nicaragua F straight cylindrical spinescent shoots of the sub-aphyllous Neltuma kuntzei G short recurved stipular spines and unijugate leaves of Xerocladia viridiramis H slender pale whitish stipular spines, unijugate leaves, and globose to ovoid-elliptic capitula of Strombocarpa strombulifera (Lam.) A. Gray I axillary nodal spine of Neltuma juliflora, central Nicaragua. Photo credits A H Kolberg, Plants of Namibia https: // herbaria. plants. ox. ac. uk / bol / Namibia B O Whaley C-F, I CE Hughes G GN Dreber https: // www. southernafricanplants. net / plantdata _ sub. php? Mspec _ ID = 6570 H Guillermo Debandi, iNaturalist (https: // guatemala. inaturalist. org / photos / 1502506).

Figure 139. Inflorescences and fruits of the genera of the Neltuma clade A capitulum of Xerocladia viridiramis Taub. B spike of Strombocarpa palmeri (S. Watson) C. E. Hughes & G. P. Lewis C spike of Strombocarpa tamarugo (Phil.) C. E Hughes & G. P. Lewis D erect spike of Neltuma rubriflora (Hassl.) C. E. Hughes & G. P. Lewis E pendulous spikes of Neltuma flexuosa (DC.) C. E. Hughes & G. P. Lewis, Antofagasta, Chile F spikes of Neltuma laevigata (Humb. & Bonpl. ex Willd.) Britton & Rose, south-central Mexico G indehiscent pods of Neltuma laevigata, south-central Mexico H unripe winged monospermous fruits of Xerocladia viridiramis in the Namib desert, Namibia I ripe fruits of Strombocarpa tamarugo, Atacama desert, northern Chile J spirally coiled indehiscent ' screw-bean' legumes of Strombocarpa strombulifera (Lam.) A. Gray. Photo credits A, H H Kolberg, Plants of Namibia https: // herbaria. plants. ox. ac. uk / bol / namibia) B, F, G CE Hughes C, I O Whaley D X Enboc- Encontro de Botanicos do Centro Oeste E P Hechenleitner J Dick Culbert.

Figure 142. Distribution of Neltuma based on quality-controlled digitised herbarium records. See Suppl. material 1 for the source of occurrence data.