Leucaena Benth., J. Bot. (Hooker) 4: 416. 1842.

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

Leucaena Benth., J. Bot. (Hooker) 4: 416. 1842.

Figs 144 , 145 , 146 , 149

Ryncholeucaena Britton & Rose, Fl. N. Amer. 23: 130. 1928. Type: Ryncholeucaena greggii (S. Watson) Britton & Rose [≡ Leucaena greggii S. Watson]

Caudoleucaena Britton & Rose, Fl. N. Amer. 23: 130. 1928. Type: Caudoleucaena retusa (Benth.) Britton & Rose [≡ Leucaena retusa Benth.]

Type.

Leucaena diversifolia (Schlecht.) Benth. [≡ Acacia diversifolia Schlecht.]

Description.

Unarmed small or medium-sized trees, 2-15 (20) m (Fig. 144D ), brachyblasts absent. Stipules persistent or caducous, ovate or subulate. Leaves bipinnate, extrafloral nectaries between proximal pair of pinnae, sometimes between other pinnae pairs and on pinnular rachis, to 75 on a single leaf ( L. trichandra (Zucc.) Urban); pinnae 1-20 (60) pairs, opposite; leaflets 3-65 (85) pairs per pinna, variable in size and shape (linear, oblong, elliptic). Inflorescences capitate, peduncle with a distal, or sub-distal involucel of united bracts, 1 (4) in leaf axils or on 1-2-branched terminal panicles exserted beyond the leaves (Fig. 145C ), composed mainly of hermaphrodite flowers, sterile flowers with staminodia absent; bracteoles subtending each flower bud persistent, peltate, sometimes exserted in bud, round, lanceolate or caudate. Flowers with 5 sepals, valvate in bud, calyx obconic, tubular or campanulate or united along mid-portion; petals 5, valvate, usually free, white or pale green; stamens 10, filaments usually white, but occasionally pink, yellow or reddish, anthers usually pilose, occasionally glabrous, usually eglandular, but sometimes the connective with a small rounded or hooded apiculum; pollen highly variable among species, occurring in monads, acalymmate polyads, or calymmate tetrahedral tetrads, tricolporate or pantoporate, exine smooth, psilate or punctate; ovary sessile or sub-sessile, glabrous or hairy, stigma narrowly funnelform. Fruits linear, flattened, (5) 10-20 (26)-seeded, valves chartaceous or coriaceous, inertly dehiscent along one or usually both sutures (Fig. 146C, D ). Seeds transverse or occasionally oblique in pod, ovate to rhomboidal, pleurogram U-shaped.

Chromosome number.

2 n = 52, 56, 104, 112 ( Cardoso et al. 2000); whole genus paleopolyploid; five documented neo-allopolyploid species ( Govindarajulu et al. 2011a); one relatively common named sterile triploid, L. x mixtec C.E. Hughes & S.A. Harris ( Hughes and Harris 1994) and one named homoploid hybrid, L. x spontanea C.E. Hughes & S.A. Harris, at the tetraploid level ( Hughes and Harris 1998).

Included species and geographic distribution.

Twenty-four species plus two named hybrids ( Hughes 1998a; Govindarajulu et al. 2011b). Mexico 11 endemic species with two extending to the USA (Texas and New Mexico) and four species to Central America; Central America five endemic species (Guatemala to Panama); one species in South America; one species pantropically introduced (Fig. 149 ).

Ecology.

Seasonally dry tropical forest and semi-arid thorn scrub; two species extending to warm temperate scrublands and one species to rainforests. Seed dispersal passive. All species deciduous. Nodulating, symbiosome present. Bee-pollinated ( Xylocopa and other smaller bees).

Etymology.

From Leucaino (Latin = becoming white), probably referring to the predominantly white stamen filaments.

Human uses.

Unripe seeds of 13 species are used as Hoffmannseggia minor foods in Mexico and are widely cultivated and incipiently domesticated in backyards in south-central Mexico ( Hughes 1998b), spawning spontaneous interspecific hybrids ( Hughes et al. 2007). One species, L. leucocephala (Lam.) de Wit, cultivated pantropically, naturalised and weedy in many places. Used in tropical agroforestry especially for livestock fodder (dubbed the alfalfa of the tropics), green manure, poles, firewood and soil conservation ( Hughes 1998b).

Notes.

The Leucaena subclade ( Leucaena , Schleinitzia , Mezcala , Kanaloa plus Desmanthus ) is equivalent to the informal Leucaena group of Hughes et al. (2003). Leucaena can be distinguished from the other genera within this subclade by its hairy anthers which are present in all but three species and which are unique within Mimoseae . The genus is the focus of various genome sequencing initiatives ( Dugas et al. 2015; Kovar et al. 2018).

Taxonomic references.

Govindarajulu et al. (2011b); Hughes (1998a, b), with illustrations; Hughes et al. (2007); Zárate (1994).

Figures

Figure 144. Habit and growth forms of genera of the Dichrostachys clade A herbaceous to weakly woody thicket of shrubby Neptunia plena (L.) Benth. in seasonally inundated ruderal habitat, Bolivia (Saerkinen 2159) B, C medium-sized to large trees of Lemurodendron capuronii Villiers & P. Guinet, north-western Madagascar (Koenen 429) D small tree of Leucaena matudae (Zarate) C. E. Hughes in seasonally dry tropical forest, Guerrero, Mexico (Hughes 2153) E shrub of Kanaloa kahoolawensis Lorence & K. R. Wood cultivated, National Tropical Botanical Garden, Kaua'i, Hawaii F small treelet of Desmanthus fruticosus Rose, Baja California, Mexico (Hughes 1532) G prostrate woody suffrutex of Desmanthus acuminatus Benth., Potosi, Bolivia (Hughes 2314) H shrub of Mimozyganthus carinatus (Griseb.) Burkart, Santa Cruz, Bolivia (Hughes 2476) I shrub of Prosopidastrum globosum (Gillies ex Hook. & Arn.) Burkart, Mendoza, Argentina J shrublet of Calliandropsis nervosa (Britton & Rose) H. M. Hern. & P. Guinet, Puebla, Mexico (Hughes 1784) K small treelet of Dichrostachys cinerea (L.) Wight & Arn., Kruger National Park, South Africa L small treelet of Alantsilodendron pilosum Villiers, S. Madagascar (Luckow 4162) M treelet of Gagnebina pterocarpa (Lam.) Baill., Madagascar N shrub of Dichrostachys venosa Villiers, in dry spiny forest, southern Madagascar. Photo credits A, D-H, J CE Hughes B, C E Koenen I Estepa Patagonica K B Dupont L M Luckow M C Commenge naturetropicale N D Du Puy.

Figure 145. Inflorescences and flowers of genera of the Dichrostachys clade A Lemurodendron capuronii Villiers & P. Guinet (Koenen 435) B inflorescence of Neptunia plena (L.) Benth., basal flowers sterile with showy yellow petaloid staminodia (Wood 26650) C inflorescence of Leucaena esculenta (Sesse & Mocino ex DC.) Benth. (Hughes 1326) D inflorescences and tergeminate leaves of Kanaloa kahoolawensis Lorence & K. R. Wood E fascicles of capitate inflorescences in axils of coevally developing leaves, Schleinitzia fosbergii Nevling & Niezgoda F inflorescences of Desmanthus bicornutus S. Watson showing basal sterile flowers with exserted white showy staminodia (Hughes 1526) G capitate inflorescences of Prosopidastrum globosum (Gillies ex Hook. & Arn.) Burkart H semi-spherical capitate inflorescences of Calliandropsis nervosa (Britton & Rose) H. M. Hern. & P. Guinet (Hughes 1784) I inflorescence of Alantsilodendron ramosum Villiers J spicate inflorescences of Gagnebina pterocarpa (Lam.) Baill., the basal flowers sterile with showy white staminodia K spicate inflorescence of Dichrostachys cinerea (L.) Wight & Arn., basal flowers sterile with showy pink staminodia L compact spikes of Dichrostachys akataensis Villiers the basal flowers sterile with showy pale pink staminodia. Photo credits A E Koenen B, C, F, H, J, K CE Hughes D A Palomino E Lauren Gutierrez G D Cabral, Flora Mondocina I, L D Du Puy.

Figure 146. Fruits of genera of the Dichrostachys clade A leaves and pod of Lemurodendron capuronii Villiers & P. Guinet, north-eastern Madagascar (Koenen 429) B Neptunia plena (L.) Benth. fruits dehiscing along the dorsal suture (Wood 26650) C ripe pods of Leucaena cruziana Britton & Rose, Oaxaca, Mexico (Hughes 1300) D cluster of unripe pods on a single inflorescence of Leucaena leucocephala (Lam.) de Wit subsp. glabrata (Rose) S. Zarate, Honduras (Hughes 1557) E ripe pods of Desmanthus leptophyllus Kunth dehiscing along both sutures (Hughes 3098) F unripe fruit of Mezcala balsensis (J. L. Contr.) C. E. Hughes & J. L. Contr., held erect, Guerrero, Mexico G ripe fruits of Mezcala balsensis dehiscing from the apex along both sutures H, I unripe and ripe fruits of Kanaloa kahoolawensis Lorence & K. R. Wood, cultivated at the Olinda rare plant propagation facility, Maui, Hawaii, USA J ripe fruits of Schleinitzia insularum (Guilemin) Burkart, the valves tardily splitting along both sutures but indehiscent K winged fruits of Gagnebina pterocarpa (Lam.) Baill., Madagascar L unripe, lomentiform fruits of Prosopidastrum globosum (Gillies ex Hook. & Arn.) Burkart which break up into one- or few-seeded fragments when ripe M ripe fruits of Mimozyganthus carinatus (Griseb.) Burkart, S Bolivia (Hughes 2476) N ripe fruits, elastically dehisced from the apex, Calliandropsis nervosa (Britton & Rose) H. M. Hern. & P. Guinet, Puebla, Mexico (Hughes 1784) O unripe coiled fruits of Dichrostachys cinerea (L.) Wight & Arn. P ripe fruits dehiscing elastically from the apex, Dichrostachys venosa Villiers, southern Madagascar Q ripe fruits of Alantsilodendron pilosum Villiers, Madagascar. Photo credits A E Koenen B-E, M, N C Hughes F, G J Luis Contreras H, I A Palomino J G McCormack, Cook Islands Biodiversity K, P, Q D Du Puy L I Specogno, Flora Mendocina O Atamari (CC-BY-SA- 3.0).

Figure 149. Distribution of Leucaena based on quality-controlled digitised herbarium records. Note that the pantropically cultivated and widely introduced species Leucaena leucocephala (Lam.) de Wit, whose true native distribution remains unknown (Hughes 1998 a), is not included in the map. See Suppl. material 1 for the source of occurrence data.