Acacia Mill.

Leguminosae, J. B. Gillett, R. M. Polhill & B. Verdcourt. Flora of Tropical East Africa. 1971

Morphology General Habit

Trees or shrubs, sometimes climbing; the native species in our area almost invariably armed with prickles or spines, the introduced ones usually unarmed

Morphology Leaves

Leaves bipinnate or (in introduced species) often modified to phyllodes (entire, leaf-like often flattened organs, without pinnae or leaflets); pinnae each with one to many pairs of leaflets; gland on upper side of petiole usually present; glands often also present at insertion of pinnae

Morphology Reproductive morphology Flowers

Flowers in spikes, spiciform racemes or round heads, hermaphrodite or male and hermaphrodite; if in heads then central flowers not enlarged and modified; inflorescences usually axillary, racemose or paniculate

Morphology Reproductive morphology Flowers Calyx

Calyx (in our species) gamosepalous, subtruncate or usually with 4–5 teeth or lobes

Morphology Reproductive morphology Flowers Corolla

Corolla 4–5(–7)-lobed

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens many (from 35–40 in A. lahai to about 215 in A. thomasii) , fertile, their filaments free or (in A. albida) connate into a tube at their extreme base only; anthers (at least some) glandular at apex, or all eglandular (in all native species glandular except in A. albida, in introduced species mostly eglandular)

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary stipitate to sessile, glabrous to puberulous

Morphology Reproductive morphology Fruits

Pods very variable, dehiscent or sometimes indehiscent, flat, ± compressed, or sometimes cylindrical, straight, curved, spiral or contorted, continuous or moniliform

Morphology Reproductive morphology Seeds

Seeds unwinged, often with a hard smooth testa, without endosperm.

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution

In the strict sense, a group of more than c. 1000 species, almost all Australian. Nine species in New Guinea, all of which also occur in Australia.

Morphology General Habit

Trees and shrubs to 40 m tall, spines usually absent

Morphology Leaves Stipules

Stipules not spinescent

Morphology Leaves

Leaves appearing simple, modified to phyllodes by expansion of the petiole, venation often more or less parallel, glands often present near top of pulvinus

Morphology Reproductive morphology Inflorescences

Inflorescences axillary or terminal, pedunculate glomerules or spikes, sometimes aggregated into panicles

Morphology Reproductive morphology Flowers

Flowers bisexual, occasionally male, uniform, 3- or 5-merous; calyx partially tubular, lobes valvate; corolla lobes fused at the base to almost completely tubular; stamens 15–200 per flower, filaments free, anthers glandular or not

Morphology Reproductive morphology Fruits

Fruits variable, dehiscent or indehiscent, straight or curved, flattened or rounded. Seeds usually elliptic to oblong, with a pleurogam, testa hard, black or brown, aril rarely present.

Ecology

In New Guinea, Acacia s.s. is a major component of the lowland monsoonal savannahs and woodlands in southern mainland New Guinea. The genus also occurs by rivers and swamps, in gallery forest, secondary forest and occasionally in rain forest.

Recognition

A very distinct group of species on account of the phyllodes: modified petioles appearing as simple leaves, usually with parallel venation; in addition, these species do not have prickles or spines.

M. Thulin et al. Flora of Somalia Vol. 1-4 [updated 2008] https://plants.jstor.org/collection/FLOS

Morphology General Habit

Trees or shrubs, sometimes climbing; the native species almost always armed with prickles or stipular spines, the introduced ones usually unarmed

Morphology Leaves

Leaves bipinnate or, in introduced species, modified to phyllodes; gland usually present on upper side of petiole, glands often also present at insertion of pinnae

Morphology Reproductive morphology Flowers

Flowers in spikes, spike-like racemes or heads, bisexual or polygamous, sometimes enclosed in bud by a ring of bracts, the involucel, the remnants of which remain on the peduncle

Morphology Reproductive morphology Flowers Calyx

Calyx usually 4–5-lobed, or subtruncate

Morphology Reproductive morphology Flowers Corolla

Corolla 4–5(–7)-lobed

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens many

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

Filaments free, or (in A. albida) connate at the base

Morphology Reproductive morphology Flowers Androecium Stamens Anthers

Anthers glandular at apex, or (in A. albida and A. saligna) eglandular

Morphology Reproductive morphology Fruits

Pods very variable, dehiscent or sometimes indehiscent, flat to ± thickened, straight, curved, spiral or contorted.

Distribution

Some 1100 species, mostly tropical and subtropical, the majority in Australia, some 40 maybe native in Africa.

Note

Acacia was subdivided along the lines indicated in vol. 1: 368 (1993), species n. 1–20, and also A. petrensis, would belong to Senegalia and species n. 22–39, as well as A. cernua, A. qandalensis and A. tephrophylla, would belong to Vachellia. Only species n. 44, A. saligna, introduced from Australia, would remain in Acacia. A. albida, according to molecular evidence, should be placed in the monotypic genus Faidherbia A. Chev. The record of A. ancistroclada Brenan from C Somalia in Kuchar, The plants of Somalia (1988) was based on Gillett & al. 21978 and 22451 that are respectively A. tortilis and A. nilotica subsp. leiocarpa. A. farnesiana L. has been reported as cultivated near Mogadishu according to Kuchar (1988). As this has not been confirmed by any specimen the record is omitted here. A. pseudonigrescens Brenan & Ross, only known from near Mustahil in SE Ethiopia may well occur in Somalia. It is a very characteristic species, apparently unarmed, with a smooth grey powdery bark and leaves with 1 pair of pinnae, each with 2 pairs of leaflets, 18–35 x 11–31 mm.

George R. Proctor (2012). Flora of the Cayman Isands (Second Edition). Royal Botanic Gardens, Kew

Morphology General Habit

Shrubs or trees, armed with prickles or unarmed; leaves bipinnate, usually with a petiolar gland; leaflets mostly small and numerous; stipules often spine-like

Morphology Reproductive morphology Flowers

Flowers in globose heads or cylindrical spikes, perfect or polygamous, usually yellow, on solitary or clustered peduncles from the leaf-axils, or in terminal panicles

Morphology Reproductive morphology Flowers Calyx

Sepals 4–5-toothed or -lobed; petals 4 or 5, more or less united

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens numerous (sometimes 50 or more), free or nearly so, exserted

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary sessile or stalked, with hair-like style; ovules 2–many

Morphology Reproductive morphology Fruits

Pods various in form, cylindrical or compressed, linear to ovate, straight, curved or contorted, membranous to woody, 2-valved or indehiscent; seeds transverse or longitudinal, usually compressed-ovoid.

Distribution

A large, widespread genus of about 500 species, most plentiful in tropical America, Africa and Australia. It is sometimes subdivided into a number of smaller genera, but these are mostly not very distinct.

Legumes of the World. Edited by G. Lewis, B. Schrire, B. MacKinder & M. Lock. Royal Botanic Gardens, Kew. (2005)

Note

Tribe Acacieae is widely attributed to Bentham (1842), e.g., Vassal (1981) and Maslin et al. (2001), but Reveal (1997) gives Dumortier (1829) as the first place of publication of the tribe and this is confirmed by Brummitt (pers. comm., 2004). The genus Faidherbia A.Chev. was included in the Acacieae by Vassal (1981), and is still retained as part of the tribe by Maslin et al. (2003). The tribal position of Faidherbia remains equivocal, although Lewis & Rico Arce (this volume) place the genus in tribe Ingeae following Polhill (1994) and Luckow et al. (2003) rendering the Acacieae monogeneric, with the single genus Acacia. The taxonomic status of Acacia and its relationship to other mimosoid genera is, however, as yet unresolved. At present three subgenera are recognised within Acacia sens. lat.: Acacia, Aculeiferum and Phyllodineae. Pedley (1986) proposed that these three subgenera be given generic rank, namely Acacia, Senegalia Raf. and Racosperma Mart., respectively, but this was not widely adopted, although the debate surrounding these suggested nomenclatural changes continues. Pedley (2003) has recently published combinations (several hundred of which are new) in Racosperma for all Australian phyllodinous acacias. What is clear is that the genus Acacia, as currently circumscribed, is not monophyletic (Maslin et al., 2003; Miller & Bayer, 2003; Miller et al., 2003), and at least five genera should be resurrected or newly described from within it in due course. The five genera correspond to those recognised by Pedley except that Senegalia sens. lat. is regarded as comprising three genera: Senegalia sens. strict., Acaciella Britton & Rose (synonym Acacia subgenus Aculeiferum section Filicinae (Benth.) Taub.), and an undescribed genus based on Acacia coulteri Benth. and a small group of related species. Acacia subgenus Acacia appears more closely related to tribe Mimoseae and subgenus Phyllodineae nests within the Ingeae in most recent studies (Luckow et al., 2003). While these two taxa are not moved out of the Acacieae in this treatment, this seems a likely future consequence of recent research. Removal of Acacia sens. strict. from the Acacieae would leave the tribe without its type genus so that Acacieae could then no longer be retained. It is not appropriate here to reinstate, change or describe new generic names, especially as application of the names Acacia and Racosperma are currently under review (Maslin et al. 2003, Orchard & Maslin, 2003; Luckow et al., submitted b). A proposal to retypify Acacia based on an Australian taxon (Orchard & Maslin, 2003) has recently been passed by the Committee for Spermatophyta but this decision awaits ratification. The present treatment of the Acacieae thus recognises a single genus containing c. 1450 species (Fig. 26).

Vernacular

florists' mimosa

Habit

Armed or unarmed trees, shrubs and lianas

Ecology

Wide ranging in habitat, from rain forest to alpine communities, dominant shrubs and trees in seasonally dry tropical and subtropical bushland, woodland, wooded grassland, coastal dunes and deserts

Distribution

Acacia sens. strict. (syn.: Acacia subg. Acacia; Vachellia), c. 161 spp., pantropical (73 in Africa and Madagascar of which c. 15 extend to Asia, 21 restricted to Asia, 7 in Australia and the Pacific; c. 60 spp. in the New World, of which c. 35 in N and C America and c. 25 in S America); Senegalia (syn.: Acacia subg. Aculeiferum sens.strict.), c. 207 spp., pantropical (69 in Africa and Madagascar, of which 7 extend to Asia, 36 restricted to Asia, 2 in Australia and the Pacific [1 extending to Asia]; c. 100 New World of which c. 40 in N and C America, c. 60 in S. America); Acaciella (syn.: Acacia subg. Aculeiferum sect. Filicinae), 15 spp. restricted to the Neotropics (mainly Mexico and C America but extending thinly to S America); Gen nov. (the 'Acacia coulteri' group), 13 spp. restricted to N and C America; 'Racosperma' (syn.: Acacia subg. Phyllodineae), c. 1045 spp. in Australia (of which 941 endemic and 7 extending to Asia, and c. 100 spp. new and yet to be described fide Maslin et al., 2003), 7 in the Pacific, 3 confined to Asia, 2 in Madagascar and the Mascarenes

Use

Leaves, fruits, wood and bark of many species are used for livestock fodder (although pods and leaves of some yield toxic cyanogenic glycosides), timber (construction, handicrafts, utensils, implements), famine food, firewood, charcoal, medicine, tanning leather (e.g., A. mearnsii De Wild., black wattle ) and oils in aromatherapy; many species important in agroforestry systems (e.g., A. mangium Willd., mangium or brown salwood , grown widely as a plantation species in Asia); some species planted as ornamentals, cut flowers of A.dealbata Link and a few other species are sold as 'florists' mimosa' ; many species are good bee forage; flowers of A. farnesiana (L.) Willd. are used in the perfume industry; several species a major source of gum arabic although A. senegal (L.) Willd. is the 'true gum arabic' ; many African species are multi-purpose trees with a wide range of local uses (see Burkill, 1995: 177-203); in Australia used in rehabilitation and soil improvement programmes, waterproof glue production, pulp, for tools, aboriginal weapons and musical instruments; seeds have minor use as human food