Borassus aethiopum Mart., Hist. Nat. Palm. 3: 221 (1838)

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Distribution

Map uses TDWG level 3 distributions (http://www.nhm.ac.uk/hosted_sites/tdwg/geogrphy.html)
Beninpresent (World Checklist of Arecaceae)B
Burkinapresent (World Checklist of Arecaceae)B
Cameroonpresent (World Checklist of Arecaceae)B
Central African Republicpresent (World Checklist of Arecaceae)B
Comorospresent (World Checklist of Arecaceae)B
Ethiopiapresent (World Checklist of Arecaceae)B
Ghanapresent (World Checklist of Arecaceae)B
Ivory Coastpresent (World Checklist of Arecaceae)B
Kenyapresent (World Checklist of Arecaceae)B
Madagascarpresent (World Checklist of Arecaceae)B
Malawipresent (World Checklist of Arecaceae)B
Mozambiquepresent (World Checklist of Arecaceae)B
Nigerpresent (World Checklist of Arecaceae)B
Nigeriapresent (World Checklist of Arecaceae)B
Northern Provincespresent (World Checklist of Arecaceae)B
Senegalpresent (World Checklist of Arecaceae)B
Sudanpresent (World Checklist of Arecaceae)B
Tanzaniapresent (World Checklist of Arecaceae)B
Ugandapresent (World Checklist of Arecaceae)B
Zairepresent (World Checklist of Arecaceae)B
Zambiapresent (World Checklist of Arecaceae)B
Zimbabwepresent (World Checklist of Arecaceae)B
Found across sub-Saharan Africa as far south as northern South Africa. Absent from parts of southwest and central Africa, and the Horn of Africa. Present on a number of offshore islands including São Tomé and Bioko in the Gulf of Guinea, three of the Cape Verde Islands, and Pemba, Zanzibar and Mayotte in the Mozambique Channel. Present in the Sambirano region of northwest Madagascar, including the islands of Nosy Bé and Nosy Mitsiou, though it may be introduced there (Bayton et al. 2003). (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Discussion

  • Historically, the key question in Borassus taxonomy has been whether to recognise both the African B. aethiopum and the Asian B. flabellifer. Most recent accounts do recognise B. aethiopum (Beccari 1924; Dransfield 1986a; 1988; Tuley 1995). The molecular study of Kovoor & Hussein (1983) also noted differences between the two species, though the population sampling was extremely limited. Qualitative characters that separate the two include the stem (ventricose in B. aethiopum and not in B. flabellifer), petiole spines (large in B. aethiopum, small in B. flabellifer), and fruit colour (black for B. flabellifer and yellow-orange for B. aethiopum). Beccari (1924) separated the African and Asian Borassus species based on the degree of division of the calyx lobes of the staminate flowers. The calyx of Asian species was divided to the base, while the calyx of African species was only divided to the middle. This character appears to be nothing more than an artefact of preparation. The calyx of most staminate flowers (of either Asian or African species) is divided to the middle. However, the transparent, membranous partitions between the calyx lobes tear easily. The resultant tear is perfectly straight, giving the impression that the calyx is divided to the base. Dransfield (1986a) noted that B. aethiopum was generally “more massive” than B. flabellifer and for several characters, this does appear to be the case. The leaves have wider petioles with longer spines and more leaflets, and the staminate and pistillate rachillae are longer with more flowers. However, while B. aethiopum and B. flabellifer are at opposite ends of the size range for some characters, other Borassus species are intermediate and no truly determinate quantitative characters were identified. The Madagascar endemic B. sambiranensis is placed here in synonymy with B. aethiopum as the two are almost indistinguishable, both in the field and the herbarium. Jumelle and Perrier de la Bâthie (1913) describe in detail the differences between the two Madagascar taxa and state that B. sambiranensis is most similar to B. aethiopum. Beccari (1912 – 14, 1914, 1924) recognised B. sambiranensis, though only the pyrenes were available for him to examine. He wrote that they resemble B. aethiopum var. bagamojensis Becc. and differ only in that there is a deep hollow at the apex. The morphology of Borassus pyrenes is extremely variable and this character alone is insufficient to warrant continued recognition of B. sambiranensis. No type specimen was cited by Jumelle and Perrier de la Bâthie, though it could be Perrier 12069 (lower Sambirano valley) (Dransfield & Beentje 1995a). However, this specimen could not be located and a modern neotype, collected in the Sambirano valley, has been designated. Borassus deleb was placed in synonymy with B. aethiopum by Dransfield (1986a), as the diagnostic fruit characters of the former fit within the range of variation exhibited by the latter. Due to their large size and fleshy consistency, few whole Borassus fruits are preserved in European herbaria. New taxa were erected on the basis of differences between these fruits without taking into account the full range of natural variation. In an attempt to counter this problem, every fruit from three Kenyan specimens of B. aethiopum (159 fruits total) was measured in the field. The variation exhibited by those fruits already encompassed almost all the variation in fruit size for the whole genus. The fruit and leaf that are illustrated as part of the type of B. deleb are not significantly different from those of B. aethiopum. Based on my own field observations and examination of the type specimen, I agree with the conclusions of Dransfield (1986a) to place B. deleb in synonymy under B. aethiopum. A neotype has been designated for B. aethiopum as the holotype is missing (Hepper 1976). The holotype was collected in Ghana near Accra (Thonning & Schumacher 1829). The neotype was also collected near Accra and includes both staminate and pistillate elements. (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Biology And Ecology

  • Riverine forest and savanna in low-lying areas, particularly on sandy or alluvial soils. Borassus aethiopum can form dense almost monospecific forest stands or is a component of more diverse riverine forest. However, it is as the main component of palm savannas for which it is best known. Borassus aethiopum is well adapted to fire and herbivory and prospers in areas with frequent burning and browsing. After the pyrenes are dispersed, the embryo is buried underground by the extending cotyledonary petiole (Barot & Gignoux 1999). The meristem is thus protected in the early years of life during a period known as the establishment phase. After several years surviving as a small cluster of leaves, the palm finally generates a stem and this grows rapidly. At this stage, the meristem is vulnerable to fire and herbivory, but is protected to some extent by the skirt of dead leaves that clothes the stem. The dead leaf blades are highly-flammable, but the woody petioles are more persistent and this may allow brush fires to pass quickly; the leaf blade is quickly consumed, but the petiole burns slowly, keeping the fire away from the meristem. As a result, the stem is covered with petioles, which may also serve as a deterrent to large herbivores as the petioles are armed with spines. The accumulated leaf sheathes and petioles are shed cleanly at maturity (Barot & Gignoux 1999). At this point, the meristem is protected from fire and herbivory by virtue of its height above the ground. (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Conservation

  • Least concern. Borassus aethiopum is widespread and common in a number of African countries. While several populations are in decline (Sambou et al. 1992; 2002), the palm remains common. Borassus sambiranensis is listed by the IUCN as endangered (EN A1c) due to habitat loss/degradation and suppression of regeneration by fire. It is perhaps unfortunate that by placing this taxon in synonymy with the widespread B. aethiopum, the conservation status of the Madagascar populations will be masked. (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Common Name

  • Dimaka (Sakalava, Madagascar), Kuhe (Ashanti, Ghana), Muhama (Kibuyu, Congo-Kinshasa), Mvumo (Kiswahili, Kenya & Tanzania). A list of West African vernacular names for B. aethiopum is provided by Burkill (1997). European names include African fan-palm, borassus-palm, rhun-palm, rônier (French) and palma-do-vinha (Portuguese). (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Etymology

Uses

  • In some parts of Africa, Borassus populations are ‘managed’ by local people, while in other areas the palm is of minimal significance. In many areas, Borassus aethiopum is restricted to game reserves and national parks where it is outside the reach of local people. The leaves are used for thatch and weaving, though species of Hyphaene are generally preferred. The palm is tapped for wine, though the process is different from that used in Asia as the apical bud is tapped rather than the inflorescences. The fruits, undeveloped endosperm and cotyledonary stalks are consumed. Burkill (1997) has reviewed the uses of Borassus aethiopum in West Africa. (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Description

  • Stem to 25m tall, almost always ventricose, to 80cm diameter. Leaves 18 – 27 in the crown; petiole and sheath 130 – 220 cm long; petiole 3.2 – 9 cm wide, robust, with large (0.4 – 2.8 cm long), recurved black teeth on the margins, yellow-orange in the distal portion, darkening to brown-black towards the trunk, though in immature plants, the petiole may be completely black; petiole spines extending along the margin of the first leaflet; costa 80 – 170 cm long; adaxial hastula conspicuous, to 2.9 cm high, abaxial hastula rudimentary; lamina radius to 190 cm maximum, dense indumentum on the ribs of some immature leaves; leaflets 86 – 120, 4.7 – 11 cm wide, apices acute and entire or splitting longitudinally with age, shortest leaflet 45 – 92 cm long, leaf divided to 58 – 95 cm; commissural veins 8 – 15 per cm, leaf anatomy isolateral. Staminate inflorescences branched to two orders, upper subtending branches terminating in 1 – 3 rachillae; rachillae green-brown and catkin-like, 37 – 50 cm long, 2.3 – 3.8 cm diameter, sometimes with a mamilliform apex; rachilla bracts form pits that contain a cincinnus of 8 – 14 staminate flowers. Pistillate inflorescences spicate; flower-bearing portion 36 – 160 cm long with 10 – 28 flowers arranged spirally. Staminate flowers 0.2 – 0.7 cm long, exserted individually from the pits; bracteoles 0.8 × 0.5 cm; calyx 0.4 × 0.2 cm and shallowly divided into three sepals, petal lobes 0.15 × 0.1 cm; stamens 6 with very short filaments, 0.02 × 0.04 cm, anthers 0.02 × 0.05 cm; pistillode minute. Pollen monosulcate, elliptical, 49 – 71 μm long, aperture 37 – 71 μm long, polar axis 32 – 61 μm long; tectum perforate, sparsely covered with supratectal gemmae. Pistillate flowers 3 × 3 cm, bracteoles 2 cm diam., sepals 1.5 × 2 cm and petals 1 × 1.5 cm. Fruits massive, 7 – 17 × 7 – 11 cm, ovoid, flattened at the apex, or with a depressed apex; fragrant, yellow to orange or red at maturity; produced inside persistent perianth segments; pyrenes 1 – 3, 6.4 – 10.9 cm × 5.4 – 8.0 cm × 4.2 – 5.7 cm, somewhat bilobed; some pyrenes have one or two external longitudinal furrows; internal flanges absent. (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A

Materials Examined

  • BURKINA FASO. Ganzourgou Prov.: Zam Dept., Rapadama, 17 Nov. 1997 (♂), Barfod 525 (AAU!); Kompienga Prov.: Pama Dept., Kabonga village, 11 Jan. 2004 (♀), Bayton & Ouédraogo 58 (K!, OUA!); Waongo village, 12 Jan. 2004 (♀ & ♂), Bayton & Ouédraogo 59, 60 (K!, OUA!); Tapoa Prov.: Arli National Park, 13 Jan. 2004 (♂), Bayton & Ouédraogo 61 (K!, OUA!); 14 Jan. 2004 (♀ & ♂), Bayton & Ouédraogo 62, 63 (K!, OUA!). CONGO-KINSHASA. Kasai-Oriental Prov.: Gandajika, no date, Liben 2817 (K!); Sud-Kivu Prov.: Impakivu- Bukavu, Kabambare, no date (♂), Christiaensen 711 (K!). CÔTE D’IVOIRE. Bas-Sassandra Region: Nero-Mer, 8 km NE of Grand-Bérébi, 12 Nov. 1963 (♂), Oldeman 625 (K!); Lagunes Region: between Bingerville and Potou Lagoon, 1907, Chevalier 20073 (P!); Savanna of Cosrou, 1962 (♀ & ♂), Leeuwenberg 4242, 4243 (K!); Sud-Comoé Region: Assinie, Danui, 1907, Chevalier 16312 (P!). ETHIOPIA. Benishangul-Gumaz Region: W of Gubla village, 13 Oct. 1996, Friis 7767 (K!); Gambela Region: 5 km S of Abobo, 22 Nov. 1995 (♀), Friis 7270 (K!). GHANA. Ashanti Region: Ejura, 1921, Chipp 773 (K!); Greater Accra Region: Accra, 1899, Sanders s.n. (K!). KENYA. Coast Prov.: Lamu Distr., Garsen (Tana River), 26 Dec. 1975 (♀ & ♂), Dransfield 4810 – 4813 (EA!, K!); Kilifi Distr., Rabai, 10 Oct. 2002 (♀ & ♂), Bayton & Obunyali 1, 2 (AAU!, EA!, K!); Kwale Distr., Pongwe, 15 Oct. 2002 (♀ & ♂), Bayton & Obunyali 14 – 16 (AAU!, EA!, K!); Mivumoni, 21 Oct. 2002 (♀ & ♂), Bayton & Obunyali 32, 33 (EA!, K!, NY!). MADAGASCAR. Antsiranana Prov.: 4 km S of Ambanja, 24 Oct. 1988 (♂), Schatz 2415 (K!, TAN!); Ananalava, 5 km SW of Maromandia, 4 July 1992 (♀ & ♂), Beentje 4708, 4709 (K!, TAN!); 16 km N of Ambanja, 26 March 2003, Bayton & Ranaivojaona 53 (K!, TAN!); 4 km S of Ambanja, 28 March 2003 (♂), Bayton & Ranaivojaona 55 (K!, P!, TAN!); Nosy Bé, Hell-Ville, 29 March 2003 (♀), Bayton & Ranaivojaona 57 (K!, TAN!). MALI. Unknown locality, 1937, Dubois 255 (P!). NIGER. Dosso Dept.: Dallol Foga, 1936, Aubreville s.n. (P!). NIGERIA. Delta State: Asaba, 1906 (♀), Unwin s.n. (FI!); Niger State: Nupe, 1859 (♂), Barter 35109 (K!); SENEGAL. Thiès Region: Sébikotane, 1935, de Wailly 4484 (P!). SOUTH AFRICA. Limpopo Prov.: Leydsdorp Distr., no date (♀), Wicht s.n. (BM!). SUDAN. Junqali State: Central Nuer District, 6 Oct. 1957 (♂), Basinski 12 (K!); Upper Nile State: Taufikia, April 1904 (♂), Brown & Brown s.n. (K!). TANZANIA. Mara Region: Ndaka Plain, 20 April 1961, Greenway 12420 (K!); Pemba South Region: Makongwe Island, 1929, Greenway 1414, 1417 (K!); Pemba Island, 19 Oct. 1931, Burtt Davy 22551 (K!); Tanga Region: Pangani, Mkwaja Ranch, 12 Sept. 1955 (♂), Tanner 2187 (BH!, K!); Mweni, 3 km S of Tanga, 5 Jan. 1976, Dransfield 4818 (K!). ZAMBIA. Southern Prov.: Mazabuka, Nampa Estates, 7 July 1963, Rensburg 1624 (K!). ZIMBABWE. Masvingo Prov.: Ndanga Distr., Mtilikwe River, 12 Dec. 1953 (♂), Wild 44830, 44909 (K!). (R.P. Bayton, A revision of Borassus L. (Arecaceae). 2007)A