Neptunia Lour., Fl. Cochinch 2: 653. 1790.
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https://dx.doi.org/10.3897/phytokeys.240.101716 |
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https://treatment.plazi.org/id/9F98A930-13C7-251C-BE39-0AD7DDAD08B3 |
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scientific name |
Neptunia Lour., Fl. Cochinch 2: 653. 1790. |
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Neptunia Lour., Fl. Cochinch 2: 653. 1790. View in CoL
Figs 144 View Figure 144 , 145 View Figure 145 , 146 View Figure 146 , 148 View Figure 148
Hemidesmas Raf., Sylva Tellur.: 119. 1838. Type: Hemidesmas plenus (L.) Raf. [≡ Neptunia plena (L.) Benth. (≡ Mimosa plena L.)]
Type.
Neptunia oleracea Lour.
Description.
Unarmed herbaceous perennials from a woody taproot (Fig. 144A View Figure 144 ), or an annual ( N. major (Benth.) Windler), sometimes a floating aquatic with enlarged, spongy, aerenchymatous stems, prostrate to erect to 1-2 (3) m. Stipules broadly ovate, occasionally narrow, striate with raised nervation when dried, usually persistent, occasionally caducous; brachyblasts absent. Leaves bipinnate, petiole sulcate, petiolar glands present or absent, crateriform; pinnae 1-11 pairs, opposite, pseudostipels sometimes present at base of pinnae; leaflets opposite, often sensitive, 6-43 pairs per pinna, linear to narrowly oblong, nearly sessile, venation brochidodromous, obscure other than central midvein, secondary venation reticulate, sometimes raised abaxially. Inflorescences of condensed cylindrical to obovate or ellipsoid spikes or capitula, 1-2 in leaf axils, pedunculate, with 2-3 lanceolate-linear to ovate-cordate bracts scattered on the peduncle, or these sometimes lacking, composed of sterile staminodial flowers proximally, hermaphrodite flowers apically, and functionally staminate flowers in between (Fig. 145B View Figure 145 ) (sterile flowers lacking in N. lutea (Leavenw.) Benth.), bracteoles subtending each flower linear, carinate, persistent. Flowers sessile; hypanthium absent; sepals valvate in bud; petals valvate; sterile flowers similar to fertile ones but smaller, lacking anthers and gynoecium, staminodia petaloid, yellow; hermaphrodite flowers with the calyx cupulate, petals 5, free, yellow, white, or pale green; stamens 5 or 10, filaments not flattened, free, anthers dorsifixed, usually bearing a semi-persistent apical claviform gland, absent in some species; pollen of tricolporate monads, exine striate; ovary sessile, usually glabrous, stigma funnelform. Fruits oblong, or when monospermous circular to broadly elliptical, dorsiventrally flattened, stipitate, often in clusters of 6 or more per inflorescence, 1-7 (20)-seeded, valves chartaceous, inertly dehiscent through both sutures, rarely through only 1 suture (Fig. 146B View Figure 146 ) or indehiscent (notably when monospermous), not internally septate, epicarp papery, dark brown, endocarp papery, buff-coloured, mesocarp absent. Seeds transverse or rarely oblique, ovate, olivaceous, smooth, unwinged, testa hard, pleurogram present.
Chromosome number.
Neptunia species comprise a polyploid series with diploids, tetraploids and hexaploids: 2 n = 26, 28, 52, 56, 72, 78 ( Turner and Fearing 1960b; Poggio et al. 2008; Santos-Silva et al. 2020).
Included species and geographic distribution.
Ca. 22 species (10 new Australian species added by Bean 2022), pantropically distributed (Fig. 148 View Figure 148 ). The genus is most speciose in Australia (14 endemics); two species in south-west USA, two in Asia, and one endemic to Brazil. The aquatic N. oleracea Lour. is widespread throughout the tropics while N. plena is most common in the Americas, but is also found in Australia and South East Asia, where it is almost certainly introduced.
Ecology.
Neptunia is unique among Caesalpinioideae in having two species with an aquatic habit, occurring by dams, or in lagoons and swampy areas with little water movement. The remaining species are terrestrial but sometimes grow in seasonally inundated riverine or other ruderal habitats. It is also one of relatively few functionally herbaceous perennial Mimoseae (a habit found elsewhere in Desmanthus , Mimosa , and Entada ). Although the majority of species are tropical, the genus also extends to warm temperate regions in the southern USA. In Australia, where the genus is most diverse, Neptunia species are generally found on heavy clay vertisols in grassland and open eucalypt woodland ( Bean 2022). Neptunia amplexicaulis Domin is one of the strongest hyperaccumulators of the metalloid element selenium (Se) in Queensland, Australia ( Bean 2022).
Etymology.
Named after the Roman god of fresh water and the sea, Neptune, in reference to the unusual aquatic habit of two species, including the type, in the genus.
Human uses.
Neptunia oleracea is a nutritious vegetable rich in vitamins and is cultivated as a food plant in Asia and Africa, where young shoots and fruits are eaten raw or cooked as a green vegetable ( Fern 2023); this species is also classified as an invasive pest in Australia (Queensland Government 2009).
Notes.
Neptunia has long been considered closely allied to members of the Dichrostachys Group ( Luckow 1993) and is robustly supported as sister to the endemic Madagascan Lemurodendron (Fig. 143 View Figure 143 ; Koenen et al. 2020a; Ringelberg et al. 2022). This sister-group relationship of Neptunia and Lemurodendron is perhaps unexpected given their divergent morphologies, but arguably Neptunia is unlike any other mimosoid because of its herbaceous (semi-) aquatic lifestyle. Neptunia can be distinguished from other genera of the Dichrostachys clade by its herbaceous habit and by its yellow petaloid staminodia on the basal sterile flowers. Some (and possibly all) Australian species of Neptunia have sensitive leaves, but, unlike in the sensitive-leaved species of Mimosa , the movement is rather slow and the leaflets often do not fold completely ( Bean 2022).
The ten new species described by Bean (2022) remain to be included in a phylogenetic analysis or to be studied cytologically. Phylogenomic analyses on Neptunia are in progress and will likely shed light on species relationships and the origins of polyploidy in the genus (Ellie Becklund, University of Ohio, USA, pers. comm.).
Taxonomic references.
Bean (2022); Cowan (1998); Nielsen (1992); Santos-Silva et al. (2020), illustrations; Windler (1966); Windler and Windler (1974).
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