Acacia mellifera
(blackthorn)

Preferred Scientific Name

• Acacia mellifera (Vahl) Benth.

Preferred Common Name

• blackthorn

Other Scientific Names

• Acacia detinens Burch.
• Acacia ferox Benth.
• Acacia mellifera (illegit)
• Acacia mellifera Benth.
• Acacia mellifera subsp. detiens (Burch.) Brenan
• Acacia mellifera subsp. detinens (Burch.) Brenan
• Acacia mellifera subsp. mellifera (=Senegalia mellifera (Vahl) L. A. Silva & J. Freitas)
• Acacia mellifera var. almakkiana S. A. Chaudhary
• Acacia senegal subsp. mellifera (Vahl) Roberty
• Acacia tenax Marloth
• Acacia vicioides Ferr. & Galim.
• Inga mellifera (Vahl) Willd.
• Mimosa mellifera M.Vahl
• Mimosa mellifera Vahl
• Senegalia mellifera (Vahl) L. A. Silva & J. Freitas
• Senegalia mellifera (Vahl) Seigel & Ebinger subsp. detinens(Burch.) Kyal. & Boatwr.

International Common Names

• English: black thorn; hook thorn; hookthorn; hook-thorn; wait a bit thorn; wait-a-bit-thorn

Local Common Names

• Egypt: khashab
• Eritrea: haq
• Ethiopia: bilili; radi a kora
• Germany: Akazie; Hakendorn
• Kenya: banyirit; bilel; curach; ebenyo; eiti; ekunoit; erenyo; habalkes; iit; iti; kathigira; kathiia; kikwata; kikwatha; kithiia; lanen; magokwe; mgoror; milikin-ki-badda; muthigira; muthiia; ng'orore; ngororo; oiti; oito-orok; panyirit; panyuriit; talamoga; talamogh; talamow
• Namibia: swarthaak
• Somalia: bilel
• South Africa: blouhaak; hakiesdoring (Afrikaans); monga (Tswana); mongangatau (Northern Sotho); monkana (Siswati); munembedzi (Tshivenda); swarthaak; swarthaak
• Sudan: ajondoke; kitr; kittir; kittur; shok
• Tanzania: kimodoa; mdugala; militimoko-hadza; miritimoko; mlugala; msasa; oete; oyeti; reketto; wait a bit thorn
• Zimbabwe: ngaga

EPPO code

• ACAMD (Acacia mellifera subsp. detinens)
• ACAML (Acacia mellifera)

Subspecies

• Acacia mellifera subsp. detinens
• Acacia mellifera subsp. mellifera

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Fabales
•                         Family: Fabaceae
•                             Subfamily: Mimosoideae
•                                 Genus: Acacia
•                                     Species: Acacia mellifera

Acacia mellifera is divided into two accepted subspecies, subsp. mellifera and subsp. detinens. A variety has also been reported, var. almakkiana, but this is not generally recognized.

The generic name Acacia comes from the Greek word akis, meaning point or barb; the species name mellifera means honey-bearing, referring to the sweet-scented flowers that are attractive to bees; and the subspecies name detinens means ‘to hold’, referring to its hooked thorns (Nonyane, 2013).

Pedley (1986) proposed a classification in which the genus Acacia was subdivided into three genera, Acacia, Senegalia and Racosperma. However, most botanists did not adopt Pedley's 1986 classification, mainly due to insufficient evidence to support the changes (Chappill and Maslin, 1995). Thus, it has been referred to as Senegalia mellifera, but this binomial is generally not accepted.

The following description is adapted from Nonyane (2013) and Biodiversity India (2019):

Acacia mellifera is a very thorny shrub to small tree, 2-5 m tall. Crown rounded or flat and spreading, with branches that may reach down to the ground. Bark light to dark grey and longitudinally fissured, fissures generally darker. Branchlets flattened, 1.5-5 mm thick, glabrous; stipules deciduous, not spinescent; spines in pairs, 3-5 mm long, black, recurved and in pairs at nodes that are only 5-15(-30) mm apart and thus there are more thorns per unit length of branch than with other species.

Leaves compound, rachis 2-5 cm long, slender, sparsely puberulous to glabrous; with 2-3(-4) pairs of pinnae, 0.5-2.5 cm long, oblong to obovate-oblong, 5-10 x 2-5 mm, unequal (acute + rounded) at the base, rounded to acute-mucronate at apex, chartaceous, green initially, the same shade above and below, leaflet margins are sparsely fringed with white hairs; but become glaucous when older; main vein subcentral with 2 prominent accessory nerves ascending about 2/3rd way up the lamina; lateral nerves prominent. There are (1-)2-3 pairs of leaflets per pinna, relatively large, 3.5-15 x 2-12 mm and 1-4 leaves per node. Petiolar gland more or less midway on petioles or at the base of at least the upper pinna pair, circular, sessile, ca 0.5 mm diameter.

The sweetly scented flowers are cream to white, becoming brownish when fading. Inflorescence are axillary spikes, up to 8 cm long, calyx obconic, ca 2 x 2 mm; teeth triangular, ca 1 mm long; corolla 2.5-3 mm long; lobes oblong, 1.5-2.5 mm long, glabrous; stamens ca 5 mm long; ovary shortly stipitate, glabrous. Pods develop rapidly after flowering, being small, straw-coloured or pale brown, greenish-brown when dry, thin to almost papery, straight, smooth, dehiscent, (2.5-)4.5-6.5(-8) cm long and (1.3-)2-2.5 mm wide, obliquely oblong, flat, thin, unlobed, rounded or obtuse-mucronate at apex, glabrous, prominently and transversely reticulate-veined; seeds 4-5.

The two subspecies differ in pinna pairs, pubescence and flowers, with subsp. mellifera usually having 2 pinna pairs and glabrous leaflets and flowers in distinct spikes, while subsp. detinens tends to have 3 pinna pairs and pubescent leaflets with a fringe of marginal hairs and flowers that appear to be in balls (actually in very shortened spikes).

Only relatively recently has A. mellifera been introduced into cultivation in India, mainly in experimental trials where its drought resistance and fast growth shows promise for land reclamation in semi-arid areas (Sastry and Kavathekar, 1990). It has also been introduced into countries in the Sahel, but no further information on introduction or potential spread is available.

However, it has spread widely within its native range, increasing in frequency and density and occupying habitats where it was previously less common. As such, it is typical of what were once referred to as ‘densifiers’, now more commonly known as ‘encroachers’ or ‘bush encroachers’, i.e. is behaving as a native invasive species. It is specifically called an invasive species in Namibia, but also shows invasive behaviour elsewhere in countries in southern Africa, East Africa and the Horn of Africa.

Soil drainage

• free
• impeded

Soil reaction

• acid
• alkaline
• neutral

Soil texture

• heavy
• medium

Special soil tolerances

• infertile
• saline
• shallow
• sodic

Natural Dispersal

The paper seed pods may be dispersed by strong winds, but are also very likely to be dispersed by water, especially after rainfall events.

Vector Transmission (Biotic)

As seed pods are readily browsed by livestock and by many wild animal species, this is likely to be the main means of seed dispersal.

In Northern Cape Province, South Africa, several rodents (Gerbillurus paeba, Desmodillus auricularis, Tatera brantsii and Tatera leucogaster) were found to assist in seed dispersal of several tree species, including A. mellifera. As most caches were found near grass tussocks, results suggest that the impact of rodents on bush encroachment is highest in habitats where bush and grass species are in close proximity (Kuechly et al., 2011).

Intentional Introduction

Acacia mellifera has been intentionally introduced to several countries for its perceived benefits as a browse species and also as a living fence.

In south-eastern Ethiopia, invasive species including A. mellifera were reported having negative impacts on livestock, livestock products and crops, although the specific impacts of each species were not assessed separately (Mussa et al., 2018).

In a study on the impact of cattle ranching on large scale vegetation patterns in a coastal savannah in Tanzania, Tobler et al. (2003) identified high amounts of three bushland types in the region, including one dominated by A. mellifera, and found that the biggest problem faced by the ranch managers was bush encroachment into pasture land.

Impact on Habitats

Acacia mellifera spreads rapidly, forming impenetrable, tangled thickets. By 1970, A. mellifera was already found to be a serious problem on 1.25 million ha in the Northern Cape and at least half of the natural pasture in Molopo, South Africa (Mostert et al., 1971), with encroachment attributed to overstocking with cattle and the absence of wild browse animals and burning, as a dense grass cover is needed to prevent the establishment of A. mellifera seedlings.

In the southern Kalahari, Botswana, bush encroachment is prevalent in semi-arid areas where A. mellifera is widespread in communal areas and private ranches, indicating rangeland degradation has been increased by land tenure changes since the 1970s (Dougill et al., 2016).

The socio-economic and environmental impacts of A. mellifera and other invasive species (A. bussei, A. seyal, A. tortilis, Argemone ochroleuca, Caesalpinia spp., Parthenium hysterophorus and Xanthium strumarium) in south-eastern Ethiopia were assessed by Mussa et al. (2018), but the study did not differentiate between the impacts of individual species. Respondents reported certain economic and ecological benefits provided by the invasive species, but also reported negative impacts on biodiversity, degrading ecosystems, on livestock and livestock products, crops and on animal and human health.

Acacia mellifera was found to modify soil water dynamics and potential groundwater recharge in invaded savannah ecosystems in Namibia (Groengroeft et al., 2018). Impacts were an increase in soil moisture larger than precipitation after some rain events, interpreted as water run-on resulting from surface ponding. There was also an overall reduction in water infiltration in the below-canopy area of A. mellifera compared to the inter-canopy space; and a faster drying of the soil in the below-canopy space because of water uptake by tree roots. These processes resulted in a potential for deep drainage about three times greater in the inter-canopy space than in the area below the canopy and thus invasion is likely to reduce groundwater recharge.

Impact on Biodiversity

Changes in landscape vegetation, forage plant composition and herding structure in pastoralist livelihoods in rangelands of northern Baringo District, Kenya point to major changes in structure and biodiversity composition over the past century, with a landscape of perennial grasses having turned into bushland dominated by A. mellifera, A. nubica and A. reficiens that have increased rapidly since the 1950s, due to high grazing pressure and restriction of pastoral mobility following the increasing numbers of humans, goats and camels (Vehrs, 2016).

Encroachment by A. mellifera appears to have a larger impact on bird diversity in grassland than in open woodland in South Africa, suggesting that shrub encroachment could be one of the main drivers of bird population dynamics in southern African savannahs and if current trends continue, the persistence of several southern African bird species associated with open savannah might be jeopardized (Kaphengst and Ward, 2008; Sirami et al., 2009).

• Invasive in its native range
• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Highly mobile locally
• Long lived
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Has high genetic variability

• Ecosystem change/ habitat alteration
• Modification of hydrology
• Modification of nutrient regime
• Modification of successional patterns
• Monoculture formation
• Negatively impacts animal health
• Reduced amenity values
• Reduced native biodiversity
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition - shading
• Rapid growth
• Produces spines, thorns or burrs

• Highly likely to be transported internationally deliberately

Social Benefit

The heartwood is termite-resistant and used for fence posts. The dark heartwood becomes almost black when oiled and highly polished and is very attractive and very hard. It is also used as fuel and for making charcoal. However, in Khomani San resettlement farms in the southern Kalahari, South Africa, A. mellifera is abundant but specifically avoided as a fuel wood, with local people preferring other species (Nott and Thondhlana, 2017).

The pods, young twigs, leaves and flowers are all highly nutritious and are eagerly eaten by livestock. A. mellifera is also mechanically harvested and chipped into ‘bush-based fodder’, where woody material is mixed with any remaining foliage and used as a dry season feed, following treatments to reduce the impacts of high levels of tannin and cellulose on animal nutrition and digestion (Pasiecznik, 2016a, b). For nutritive value and tannin content of A. mellifera, see Osuga et al. (2007) and Ondiek et al. (2017) in Kenya, Nassoro et al. (2015) in Tanzania.

In areas where it occurs naturally, it provides good shade for livestock and given its numerous qualities, A. mellifera was also considered to show promise as a species for live fencing (Diagne et al., 2006).

Flowers are sweetly scented and are attractive to bees. Nonyane (2013) also consider that is has ornamental value and that it is worth cultivating for its fine floral display.

Acacia mellifera is widely used in traditional African medicines against various diseases such as pneumonia and malaria, with bark extracts exhibiting anti-bacterial and anti-fungal activity, active against Staphylococcus aureus, Microsporum gypseum and Trichophyton mentagrophytes. These results may partly explain and support the use for the treatment of infectious diseases in traditional medicine in Kenya (Mutai et al., 2009). Plant extracts are also reported to be used in traditional medicine in South Africa (Twilley et al., 2017) and are used to treat chronic joint pain in Kenya (Wambugu et al., 2011). In southern Africa, A. mellifera twigs are also chewed and used as toothbrush sticks (Nonyane, 2013).

Environmental Services

Leaves, small twigs and pods are very nutritious and in southern Africa it is commonly browsed by wild animals such as black rhino (Diceros bicornis), kudu (Tragelaphus strepsiceros), eland (Taurotragus oryx) and giraffe (Giraffa).

Draft datasheet under review