Vachellia Wight & Arn., Prodr. Fl. Ind. Orient. 1: 272. 1834.

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

Vachellia Wight & Arn., Prodr. Fl. Ind. Orient. 1: 272. 1834.

Figs 162 , 163

Aldina E. Mey., Comment. Pl. Africae Austr. 171. 1836, nom. illeg., non Aldina Adans. (1763) nom. rej., nec Aldina Endl. 1840. nom. cons. Type not designated.

Farnesia Gasp., Deser. Nuov. Gen. 1838, non Farnesia Heist. ex Fabr., Enum. Pl. Hort. Helmstad. ed. 2, 400. 1763. Type: Farnesia odora Gasp., nom. illeg. [= Mimosa farnesiana L. (≡ Vachellia farnesiana (L.) Wight & Arn.)]

Gumifera Raf., Sylva Tellur.: 118. 1838. Lectotype: Gumifera nilotica (L.) Raf. [≡ Mimosa nilotica L. (≡ Vachellia nilotica (L.) P.J.H. Hurter & Mabb.)]

Poponax Raf., Sylva Tellur.: 118. 1838. Type: Poponax tortuosa (L.) Raf. [≡ Mimosa tortuosa L. (≡ Vachellia tortuosa (L.) Seigler & Ebinger)]

Delaportea Thorel ex Gagnep., Notul. Syst. (Paris) 2: 118. 1911. Type: Delaportea armata Thorel ex Gagnep. [≡ Pithecellobium harmandianum Pierre (≡ Vachellia harmandiana (Pierre) Maslin, Seigler & Ebinger)]

Pithecodendron Speg., Physis (Buenos Aires) 6: 313. 1923. Type: Pithecodendron argentinense Speg. [= Mimosa horrida L. (≡ Vachellia horrida (L.) Kyal. & Boatwr.)]

Nimiria Prain ex Craib, Bull. Misc. Inform. Kew 1927: 393. 1927. Type: Nimiria siamensis Craib [≡ Vachellia siamensis (Craib) Maslin, Seigler & Ebinger]

Acaciopsis Britton & Rose, N. Amer. Fl. 23: 93. 1928. Type: Acaciopsis pringlei (Rose) Britton & Rose [≡ Acacia pringlei Rose (≡ Vachellia pringlei (Rose) Seigler & Ebinger)]

Bahamia Britton & Rose, N. Amer. Fl. 23: 86. 1928. Type: Bahamia acuifera (Benth.) Britton & Rose [≡ Acacia acuifera Benth. (≡ Vachellia acuifera (Benth.) Seigler & Ebinger)]

Feracacia Britton & Rose, N. Amer. Fl. 23: 86. 1928. Type: Feracacia daemon (Ekman & Urb.) Britton & Léon [≡ Acacia daemon Ekman & Urb. (≡ Vachellia daemon (Ekman & Urb.) Seigler & Ebinger)]

Fishlockia Britton & Rose, N. Amer. Fl. 23: 91. 1928. Type: Fishlockia anegadensis (Britton) Britton & Rose [≡ Acacia anegadensis Britton (≡ Vachellia anegadensis (Britton) Seigler & Ebinger)]

Lucaya Britton & Rose, N. Amer. Fl. 23: 87. 1928. Type: Lucaya choriophylla (Benth.) Britton & Rose [≡ Acacia choriophylla Benth. (≡ Vachellia choriophylla (Benth.) Seigler & Ebinger)]

Myrmecodendron Britton & Rose, N. Amer. Fl. 23: 91. 1928. Type: Myrmecodendron hindsii (Rose) Britton & Rose [≡ Acacia hindsii Benth. (≡ Vachellia hindsii (Benth.) Seigler & Ebinger)]

Tauroceras Britton & Rose, N. Amer. Fl. 23: 85. 1928. Type: Tauroceras spadicigerum (Schltdl. & Cham.) Britton & Rose [≡ Acacia spadicigera Schltdl. & Cham. (= Vachellia cornigera (L.) Seigler & Ebinger)]

Acacia Mill. subg. Acacia sensu Vassal, Bull. Soc. Hist. Nat. Toulouse 108: 139. 1972.

Lectotype

(designated by Ross 1975b: 465, 471). Vachellia farnesiana (L.) Wight & Arn. [≡ Mimosa farnesiana L.] [Linnaean Plant Name Typification Project (2022); illustration at S, IDC 214.5]

Description.

Shrubs or trees, 0.5-30 m, rarely a prostrate shrub; bark mostly dark to light brown to black or grey, rarely whitish-reddish to yellowish, and papery, peeling or corky, with most species commonly rough to furrowed; brachyblasts usually present; prickles absent. Stipules spinescent, woody, paired at the nodes, straight to curved, sometimes asymmetrical, in some species enlarged and inhabited by ants, occasionally exceeding 200 mm long; a number of African species with galls subtending the spines. Leaves caducous (sometimes evergreen), alternate and also commonly clustered (2-8) on short shoots, these brachyblast leaves usually smaller and with fewer pinna pairs and leaflets than the alternately arranged leaves on fast growing branches; petioles with one or more extrafloral nectaries, often with one to several on the rachis, most commonly between the pinna pairs; pinnae 1-many (60+) pairs, mostly opposite; leaflets 1-many (70+) pairs per pinna, mostly opposite, sessile to subsessile, the apex in most American myrmecophytes bearing a small yellow detachable Beltian body. Inflorescences capitula to cylindrical spikes, solitary or clustered in leaf axils or on short shoots, rarely in pseudo-racemes or pseudo-panicles, sometimes andromonoecious; peduncles with a small involucel, usually medial or basal, rarely at the base of the inflorescence. Flowers bracteate, sessile to subsessile, actinomorphic; calyx 4-5 (6)-lobed; corolla 4-5 (6)-lobed; stamens 20-100, yellow to gold or creamy white, filaments usually separate to the base or occasionally shortly fused (or rarely and irregularly a greater degree of fusion), exserted, anthers small, dorsifixed, apical glands often present; pollen in polyads of 16 (8, 12, 24, 32, 48) grains, colporate with the exine surface psilate and nexine with columellae ( Guinet and Vassal 1978; Guinet 1981b; Caccavari and Dome 2000; Maslin et al. 2003; Miller and Bayer 2003; Duarte et al. 2021); nectary disc absent; ovary sessile to subsessile. Fruits mostly dehiscing along both sutures, occasionally indehiscent, linear to oblong, straight to falcate, flattened to terete, a pericarpic strip (papyraceous mesocarp) sometimes present inside each valve in some species. Seeds uniseriate or biseriate to irregularly arranged, (4) 6-12 (14) per fruit if uniseriate, to 22 (40) if biseriate, sometimes surrounded by pulp, ovoid to ellipsoid, often flattened, testa hard, pleurogram large to small; funicle filiform, not enlarged arillate (Fig. 162 ).

Chromosome number.

x = 13. Many American species of Vachellia are diploids with 2 n = 26 ( Atchison 1948; Darlington and Wylie 1956; Turner 1959; Turner and Fearing 1960a; Hamant et al. 1975; Goldblatt and Johnson 1979 -; Rico-Arce 2007; Rice et al. 2015). A smaller number of African species are diploids and several are tetraploid, whereas others have higher ploidy levels ( Ross 1979). Among Asian species, a number in India have 2 n = 26, 52 and/or 78 ( Chakrabarty and Gandopadhyay 1996; Gómez-Acevedo and Tapia-Pastrana 2003).

Included species and geographic distribution.

Vachellia (164 species in total) is represented by 61 species (some with forms and varieties) in the Americas, 75 in Africa and Madagascar, nine in Australia and the Pacific, and 33 in Asia (including about 15 also found in Africa) ( Maslin et al. 2003; Maslin 2015; WorldWideWattle 2022). A strong geographical element (America vs Africa + Asia + Australia) is evident in the relationships amongst Vachellia species worldwide ( Miller and Seigler 2012; Kyalangalilwa et al. 2013; Boatwright et al. 2015; Comben et al. 2020) (Fig. 163 ).

Vachellia is widespread in most tropical and many subtropical areas of the world. A few species enter warm temperate regions but their distribution is generally limited to areas that lack killing frosts. Vachellia nilotica and V. farnesiana have been widely introduced into the Old and New World, respectively. The latter has a pantropical distribution and, including probable introductions, is the most widely distributed of all members of the genus.

Ecology.

Many members of Vachellia are tenacious, spiny and invasive. Although most species favour disturbed, arid sites from sea level to ca. 2800 m, others (e.g., V. mayana (Lundell) Seigler & Ebinger) are limited to relatively undisturbed rainforests. Species are known from many forest types including primary and secondary tropical evergreen forests, rainforests, semi-deciduous forests, dry and wet secondary forests, montane, gallery, riverine forests, and are frequently found in Quercus-Juniperus woodlands, but uncommonly in secondary vegetation of cloud forests and ground water forests in Africa ( Ross 1979). Vachellia species are also frequent in dry, deciduous scrub vegetation, xerophytic scrub, river valley scrub, thornveld, bushveld, semi-desert scrub, caatinga, chaco scrub, bushlands, grasslands, savanna grasslands, dwarf-tree grasslands, and wooded grasslands.

They are associated with many soil types including sands, clay, serpentine soils, volcanic soils, limestone and rocky limestone soils, karst limestone, coastal dunes, granitic washes, loam, saline soils, heavy black soils, gravelly soils, Kalahari sands, seasonally flooded alluvium, black cotton soils, hard-pan grey soils, dry water courses, margins of seasonal swamps, and they sometimes grow on termite mounds ( Ross 1979).

Etymology.

Vachellia was named in honour of the Reverend George Harvey Vachell (1799-1839), a collector of the flora of China.

Human uses.

Vachellia species are often used for firewood and for making charcoal and are the major source of fuel in many areas of the world. They often serve as forage for livestock especially in times of drought ( Cheatham et al. 1995; Chakrabarty and Gandopadhyay 1996; Smit 1999; Rico-Arce 2007). The wood has been used for construction of houses, for making furniture, tool handles, digging sticks, ploughs, cart wheels, fence posts, bows and arrow shafts and various objects. Only a few species such as V. leucophloea (Roxb.) Maslin, Seigler & Ebinger are important for lumber. The inner bark of this species and others is used for making twine and fiber for fishnets and cordage ( Chakrabarty and Gandopadhyay 1996). Tannins from bark and pods of Vachellia species have been used to tan leather and extracts of the bark have also been used to prepare permanent black ink ( Smit 1999).

A number of especially spiny species are grown for living fences. In Africa these are used to surround kraals. Others, such as Vachellia leucophloea and V. nilotica , are planted along roadsides and in gardens. Some are grown as shade trees for coffee, cacao and other crops ( Chakrabarty and Gandopadhyay 1996). In the Americas species such as V. constricta (Benth.) Seigler & Ebinger are used as ground covers and ornamentals in landscaping ( Cheatham et al. 1995).

Vachellia farnesiana and V. caven (Molina) Seigler & Ebinger were early introduced into Spain, France and Italy ( Bell et al. 2017). The fragrances from the flowers are commonly used in perfumes. Egypt is presently the most important producing country. Although the foliage, fruits and seeds of many species are toxic to humans as well as to other animals, they often serve as fodder for livestock and in some instances are eaten by humans. Others are used as components of traditional medicine ( Cheatham et al. 1995).

Notes.

The genus Vachellia was once part of a widely circumscribed Acacia Mill., and as first described by Miller (1754), Acacia had a type that now belongs to Vachellia . Many of the species later placed in Acacia were included in a larger genus Mimosa but Bentham (1841a, 1842a, b) narrowed the concept of Acacia and later he restricted his tribe Acacieae and divided the genus Acacia into six series ( Bentham 1875). Vassal (1972), in turn, described three subgenera, viz Acacia , Aculeiferum , and Heterophyllum (Phyllodineae) , from these series. Pedley (1986) concluded that Acacia was too broadly conceived and suggested that it be subdivided into three genera, Acacia , Senegalia Raf., and Racosperma Mart. Around the turn of the century, the results of molecular studies began to support such a division. At approximately the same time, a proposal was put forth to recognise an Australian species, A. penninervis Sieber ex DC., as the new type for a more narrowly circumscribed genus Acacia ( Orchard and Maslin 2003). After much controversy, the name Acacia supplanted Racosperma. A consequence of these decisions was that species formerly recognised as Acacia sensu Pedley (1986) then became Vachellia .

No intrageneric classification has yet been published for Vachellia . Major works that present descriptions and/or keys include: Ebinger et al. (2000) and Rico-Arce (2007) for the Americas, Ross (1979) for Africa and Du Puy and Villiers (2002) for Madagascar, Nielsen (1981b, 1985a, 1992) for South East Asia and Malesia, and Orchard and Wilson (2001) for Australia, all under the name Acacia .

Vachellia species can readily be distinguished from other members of Acacia s.l., and especially the large segregate genus Senegalia that is also common in both Old and New World tropics, by the presence of stipular spines, the absence of prickles, the presence of an involucre on the peduncle, the absence of a torus-shaped nectary at the base of the ovary or ovary stalk, pollen polyads with colporate apertures and nexine possessing columellae, and different seedling development ( Vassal 1972; Maslin et al. 2003; Seigler and Ebinger 2005). Characters that Vachellia shares with Senegalia include capitate, oblongoid or spicate inflorescences, and flowers that have numerous stamens (20-100).

Most Vachellia species have sessile petiolar glands, usually near the lowermost pair of pinnae, and smaller rachis glands are commonly found between the upper one or more pairs of pinnae. These glands, at least during the rapid growth associated with flower development, appear to produce a food reward for pollinators and various insects, especially ants.

The flower-heads of Vachellia species are visited by large numbers of different insects, especially bees, occasionally birds, and rarely by bats; however, pollination biology has only been examined in detail for a few species ( Stone et al. 2003). Pollen is the principal floral reward but although a nectary disc is absent, nectar is produced in a minority of species ( Stone et al. 2003). The inflorescences are commonly sweetly scented although the odour in V. rigidula (Benth.) Seigler & Ebinger is foetid.

Seeds of the swollen-thorn American Vachellia species are dispersed by birds ( Janzen 1974). Some African species are dispersed by a range of ungulates, including giraffes and several species of antelopes, and by ostriches ( Miller 1996).

Twelve Neotropical myrmecophytes share many adaptive ecological and morphological traits, most of which appear to be related to their mutualistic association with acacia-ants of the genus Pseudomyrmex Lund, 1831 ( Janzen 1967a, 1967b, 1974). These species of Vachellia have inflated stipular spines usually inhabited by ants. Near the tip of many of these inflated spines, a small entrance hole is made by the ant queen when the spines are young and soft. Detachable tips, known as Beltian bodies after Thomas Belt, are found on the leaflets of most of the ant-acacias and they are rich in lipids, sugars and proteins. They are small, yellowish, ovoid to ellipsoid structures, about 3 mm long, and used as a food source by the ant-larvae. They are thought to have evolved in a symbiotic relationship with ants.

In approximately 11 species of African Vachellia , the stipular spines are distinctly and characteristically swollen into structures commonly known as ant-galls. These species are sometimes called Whistle Thorn acacias because of the noise caused by wind blowing over the ant entry holes. These galls are often inhabited by ants, commonly those of the genus Crematogaster Lund, 1831.

A number of hybrids have been identified in both Africa ( Ross 1979, as Acacia ) and the Americas where most Vachellia hybrids appear to be rare or uncommon, although swarms involving V. macracantha (Humb. & Bonpl. ex Willd.) Seigler & Ebinger, V. pennatula (Schltdl. & Cham.) Seigler & Ebinger, and V. campeachiana (Mill.) Seigler & Ebinger are common in central Mexico ( Ebinger and Seigler 1987, 1992; Clarke et al. 2005).

Taxonomic references.

Ali (1973); Chakrabarty and Gandopadhyay (1996); Comben et al. (2020); Deshpande et al. (2019); Du Puy and Villiers (2002); Ebinger et al. (2000); Kodela and Wilson (2006); Kyalangalilwa et al. (2013); Lewis (1987); Lock (1989); Lock and Simpson (1991); Maslin (2015); Maslin et al. (2003, 2019a); Miller and Seigler (2012); Nielsen (1981b, 1985a, 1992); Orchard and Wilson (2001); Queiroz (2009); Ragupathy et al. (2014); Rico-Arce (2007); Ross (1975b, 1979, 1981); Smit (1999).

Figures

Figure 162. Morphological features of Vachellia A branches with spicate inflorescences of V. rigidula (Benth.) Seigler & Ebinger B habit of V. bidwillii (Benth.) Kodela (M. Simmons 3191) C inflorescences and leaves of V. farnesiana (L.) Wight & Arn. D habit of V. farnesiana E gall and spines of V. drepanolobium (Harms ex Y. Sjoestedt) P. J. H. Hurter F spines and inflorescences of V. cornigera (L.) Seigler & Ebinger (Seigler 16051) G partial leaf of V. cornigera with Beltian Bodies (Tamaulipas, Mexico) (Seigler 15962) H fruit of V. caven (Molina) Seigler & Ebinger I habit of V. schaffneri (S. Watson) Seigler & Ebinger J leaves and stems of V. karroo (Hayne) Banfi & Galasso K inflorescences and leaves of V. nilotica subsp. indica (Benth.) Kyal. & Boatwr. (Simmons 1032) L fruits of V. nilotica subsp. kraussiana (Benth.) Kyal. & Boatwr. Photo credits A D Seigler B, K J Simmons C, J S Navie D, F, G, I B Maslin E T Nicholls, Nature Education Center H RT Queiroz http: // rubens-plantasdobrasil. blogspot. com / L D Kunjithapatham.

Figure 163. Distribution of Vachellia based on quality-controlled digitised herbarium records. The map includes records for introduced / naturalised taxa as well as native ones. For instance, most records in eastern Brazil are due to V. farnesiana, which is naturalised there. The Indian subcontinent may be under-sampled (see Deshpande et al. 2019). See Suppl. material 1 for the source of occurrence data.