Borassus aethiopum Mart.

Bayton, R. (2007). A Revision of Borassus L. (Arecaceae). Kew Bulletin, 62(4), 561-585. Retrieved from http://www.jstor.org/stable/20443389

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; 2-002), the palm remains common. Borassus sambiranensis is listed by the IUCN as endangered (EN A1 c) 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.

Distribution

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).

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 sheaths 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.

Morphology Leaves

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.

Morphology Reproductive morphology Flowers

Staminate flowers 0.2 - 0.7 cm long, exserted individually from the pits; bracteoles 0.8 x 0.5 cm; calyx 0.4 x 0.2 cm and shallowly divided into three sepals, petal lobes 0.15 x 0.1 cm; stamens 6 with very short filaments, 0.02 x 0.04 cm, anthers 0.02 x 0.05 cm; pistillode minute Pistillate flowers 3 x 3 cm, bracteoles 2 cm diam., sepals 1.5 x 2 cm and petals 1 x 1.5 cm

Morphology Reproductive morphology Flowers Pollen

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

Morphology Reproductive morphology Fruits

Fruits massive, 7- 17 x 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 x 5.4 - 8.0 cm x 4.2 - 5.7 cm, somewhat bilobed; some pyrenes have one or two external longitudinal furrows; internal flanges absent.

Morphology Reproductive morphology Inflorescences

Pistillate inflorescences spicate; flower-bearing portion 36 - 160 cm long with 10 - 28 flowers arranged spirally 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.

Morphology Stem

Stem to 25m tall, almost always ventricose, to 80cm diameter

Note

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. 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. 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. 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. 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. Aethiopia' was a general term used by the ancient Greeks and Romans for Africa south of Libya and Egypt.

Type

Ghana, Thonning 258 (holotype lost, see Hepper, 1976: 154); Ghana, Weija, 24 April 1957 (Q & Cf), Tomlinson s.n. (neotype, chosen here, BH!).

Vernacular

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).

Palmae, T. A. Russell. Flora of West Tropical Africa 3:1. 1968

Morphology General Habit

The tallest of African palms, often 70 ft. high and sometimes as much as 100 ft.

Morphology Trunk

Trunk swollen above the middle

Ecology

In dry savanna.

Note

The palm is dioecious, the female conspicuous by its large orange fruits.

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.

Vernacular

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).

Distribution

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).

Biology

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.

General 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.