Acaciella Britton & Rose, N. Amer. Fl. 23(2): 96. 1928.

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

Acaciella Britton & Rose, N. Amer. Fl. 23(2): 96. 1928.

Figs 197 , 198 , 199 , 200

Acacia ser. Filicinae Benth., London J. Bot. 1: 322. 1842. Type not designated.

Acacia sect. Filicinae (Benth.) Taub., Nat. Pflanzenfam. 3(3): 113. 1894. Type not designated.

Senegalia sect. Filicinae (Benth.) Pedley, Bot. J. Linn. Soc. 92(3): 238. 1986. Type: Senegalia angustissima (Mill.) Pedley [≡ Mimosa angustissima Mill. (≡ Acaciella angustissima (Mill.) Britton & Rose)]

Type.

Acaciella villosa (Sw.) Britton & Rose [≡ Mimosa villosa Sw.]

Description.

Shrubs or small trees to 12 m (Fig. 197A, B ), rarely perennial herbs, always unarmed. Stipules leafy, ephemeral or rarely persistent, to 5 (10) mm. Leaves bipinnate; petioles and rachis without extrafloral nectaries; pinnae 2-25 pairs; leaflets 1-30 pairs per pinnae, predominantly small (to 12 mm long) but very large (to 3-6.5 cm) in some species. Inflorescences capituliform, sometimes elongated into short racemes, pedunculate, often organised in long efoliate terminal panicles (Fig. 198A, B ); inflorescence units homomorphic. Flowers bracteate, the bracts caducous, pedicellate, the pedicels persistent after the flowers have fallen; calyx cup-shaped, 5-merous, the lobes less than ¼ the length of the calyx tube to almost truncate; corolla 5-merous, the lobes more than ½ the whole corolla length; stamens always numerous (Fig. 198B ), sometimes to 300 in a single flower, exserted from the corolla, always free and white, drying yellow, orange or pink; anthers eglandular; pollen in 8-grained polyads; ovary stipitate, the stipe sometimes ¼ the length of the ovary. Fruits linear to narrowly oblong, flattened, straight, mucronate and stipitate, with thickened margins, the valves membranous or chartaceous (Fig. 199A ), dehiscing along both margins from apex downwards, seeds up to 8 (12) per pod. Seeds lenticular or spherical, dark brown, with a prominent U-shaped pleurogram.

Chromosome number.

2n = 26 [ A. texensis (Torr. & A.Gray) Britton & Rose] ( Rico and Bachman 2006).

Included species and geographic distribution.

Fifteen species are currently recognised (Rico Arce and Bachman 2006), all restricted to the Neotropics. With the exception of A. glauca (L.) L. Rico, all species of Acaciella occur in Mexico, and 11 of them are endemic to this country. Species have been recorded from south-eastern United States, throughout Mexico and south to Costa Rica and western Panama in Central America, with scattered records in the Antilles (Cuba, Jamaica and Dominican Republic), and South America (Venezuela, Colombia, Ecuador, Peru, Bolivia and Argentina). The genus is absent in the Amazonian basin (Fig. 200 ).

Ecology.

Sea level to 2500 m elevation, primarily in areas covered by seasonally dry tropical deciduous forests, thorn scrub, semi-desert vegetation, and mixed Quercus-Pinus forest.

Etymology.

Small Acacia , from - ellus (suffix) used to form diminutives.

Human uses.

In its native range, the leaves of A. angustissima are reported to be used as forage for livestock, the roots for tanning, and different parts of the plants are utilised in traditional medicine and for the production of fermented beverages (Rico Arce and Bachman 2006). In addition, due to its high growth-rate and its ability to fix atmospheric nitrogen and accumulate tannins, A. angustissima is being tested as a multi-use, agroforestry species (Rico Arce and Bachman 2006; Rincón-Rosales and Gutiérrez-Miceli 2008; Musara and Aladejana 2020). However, in Asia and Australia, due to its high capacity to naturalise, it has been perceived as a potential weed.

Notes.

Acaciella has traditionally been related to Acacia Mill. s.l., and species were grouped into Acacia ser. Filicinae Benth. ( Bentham 1842b), regarded by Pedley (1978) as sect. Acaciella Filicinae . A few years later, Acacia ser. Filicinae was transferred to genus Senegalia Britton & Rose, as sect. Filicinae (Benth.) Pedley ( Pedley 1986).

Despite the resemblance of the flowers of Acaciella to those of Acacia , Rico Arce and Bachman (2006) resurrected Acaciella as a distinct genus, based on a combination of morphological traits, essentially the lack of spines and extrafloral nectaries, and 8-grained polyads (Rico Arce and Bachman 2006). Gómez-Acevedo et al. (2010), using morphological and molecular evidence, established Acaciella [excl. A. chamelensis (L. Rico) L. Rico] as monophyletic and phylogenetically related to Calliandra rather than to Acacia .

Taxonomic references.

Britton and Rose (1928); Rico Arce and Bachman (2006).

Figures

Figure 197. Diversity of plant growth forms of the genera of the Calliandra clade A shrubby habit of Acaciella angustissima (Mill.) Britton & Rose var. angustissima, Texas, USA B treelet of Acaciella angustissima var. angustissima, Chiquimula, Guatemala (Hughes 1487) C shrub of Calliandra mollissima (Humb. & Bonpl. ex Willd.) Benth., Maranon Valley, Peru (Saerkinen 2198) D stunted xerophytic shrublet of Afrocalliandra redacta (J. H. Ross) E. R. Souza & L. P. Queiroz, Kuboes, South Africa E stunted xerophytic shrublet of Calliandra chilensis Benth., northern Chile F small treelet of Calliandra calothyrsus Meisn., Siguatepeque, Honduras G shrub of Calliandra californica Benth., Baja California Sur, Mexico (Hughes 1546) H treelet of Calliandra fuscipila Harms, Serra do Espinhaco, Bahia, Brazil (Queiroz 15626) I, J functionally herbaceous geoxyle of Calliandra longipes Benth. arising from a stout lignotuber and resprouting and fruiting after fire in savanna woodland, Santa Cruz, Bolivia (Wood 26548) K geoxylic shrublet of Calliandra mucugeana Renvoize, arising from a stout woody underground stem and forming carpet-like thickets, Serra do Espinhaco, Bahia, Brazil (Queiroz 15540). Photo credits A Ron Stephens, iNaturalist (https: // www. inaturalist. org / photos / 199321699) B, C, F-K CE Hughes D Pietermier, iNaturalist (https: // www. inaturalist. org / photos / 152398478) E J Jimenez Castillo.

Figure 198. Variation in inflorescences of the genera of the Calliandra clade. A compound terminal panicle of capitula of Acaciella villosa (Sw.) Britton & Rose, Oaxaca, Mexico (Hughes 1333) B capitula of Acaciella villosa, Piura, Peru (Hughes 2635) C flowers of Afrocalliandra redacta (J. H. Ross) E. R. Souza & L. P. Queiroz, Kuboes, South Africa D erect terminal racemose inflorescence of Calliandra calothyrsus Meisn. flowering at night, Siguatepeque, Honduras (Macqueen 3) E erect terminal racemose inflorescence of Calliandra juzepczukii Standl., Oaxaca, Mexico (Hughes 1675) F erect terminal inflorescence with buds and flowers opening acropetally, Calliandra grandiflora (L'Her.) Benth., Mexico City, Mexico G inflorescence of Calliandra taxifolia (Kunth) Benth., Mollendo, Arequipa, Peru (Hughes 2357) H heteromorphic inflorescence of Calliandra mollissima (Humb. & Bonpl. ex Willd) Benth., Maranon Valley, Peru, showing central flowers with enlarged staminal tubes (Saerkinen 2198) I Calliandra nebulosa Barneby, Serra do Espinhaco, Bahia, Brazil (Queiroz 15624) J flowers of Calliandra longipinna Benth., Serra do Espinhaco, Bahia, Brazil (Queiroz 15603) K long pedicellate flowers of Calliandra leptopoda Benth., Serra do Espinhaco, Bahia, Brazil L leaves, foliaceous stipules and terminal inflorescences of Calliandra lanata Benth., Serra do Espinhaco, Bahia, Brazil. Photo credits A, B, D, E, G-J CE Hughes C Pietermier, iNaturalist (https: // www. inaturalist. org / photos / 15308160) F Mvz-juangonzalezromero, iNaturalist (https: // www. inaturalist. org / photos / 195966667) K, L E de Souza.

Figure 199. Variation in fruits across genera of the Calliandra clade A pendulous fruit of Acaciella angustissima (Mill.) Britton & Rose var. angustissima, Chiapas, Mexico B erect fruit and spinescent stipules of Afrocalliandra redacta (J. H. Ross) E. R. Souza & L. P. Queiroz, Kuboes, South Africa C, D fruits of Calliandra taxifolia (Kunth) Benth., Mollendo, Arequipa, Peru (Hughes 2357) C unripe green erect fruits D ripe fruits elastically dehiscent from the apex, the valves recurved backwards E ripe and unripe fruits of Calliandra luetzelburgii Harms, Serra do Espinhaco, Bahia, Brazil (Queiroz 15618) F unripe, green, erect fruits of Calliandra viscidula Benth., Serra do Espinhaco, Bahia, Brazil (Queiroz 15541) G, H fruits of Calliandra houstoniana (Mill.) Standl., Chiapas, Mexico (Hughes 1271 & 1287) I unripe fruits of Calliandra chilensis Benth., northern Chile J unripe, erect fruits of Calliandra bahiana Renvoize var. erythematosa Barneby, Serra do Espinhaco, Bahia, Brazil (Queiroz 15622). Photo credits A Neptali Ramirez Marcial, iNaturalist (https: // www. inaturalist. org / photos / 199788369) B Pietermier, iNaturalist (https: // www. inaturalist. org / photos / 152398411) C-H, J CE Hughes I J Jimenez Castillo.

Figure 200. Distribution of Acaciella based on quality-controlled digitised herbarium records. See Suppl. material 1 for the source of occurrence data.