Leucaena Benth., J. Bot. (Hooker) 4: 416. 1842.
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https://dx.doi.org/10.3897/phytokeys.240.101716 |
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https://treatment.plazi.org/id/2DF81610-1B8D-6147-7591-A7D3C5505AB7 |
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scientific name |
Leucaena Benth., J. Bot. (Hooker) 4: 416. 1842. |
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Leucaena Benth., J. Bot. (Hooker) 4: 416. 1842. View in CoL
Figs 144 View Figure 144 , 145 View Figure 145 , 146 View Figure 146 , 149 View Figure 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 View Figure 144 ), 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 View Figure 145 ), 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 View Figure 146 ). 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 View Figure 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).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.