Borassus madagascariensis (Jum. & H.Perrier) Bojer ex Jum. & H.Perrier

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

Type

none cited; Madagascar, Mahajanga Prov.: Marovoay, 14 March 2003 (9), Bayton & Ranaivojaona 44 (neotype, chosen here, K!, P!, TAN!).

Morphology Stem

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

Morphology Leaves

Leaves 16 - 23 in the crown; petiole and sheath 170 - 237 cm long; petiole 7.8 - 9.2 cm wide at midpoint, robust, yellow-green along the whole length, margins with small serrate black teeth, 0.1 - 0.85 cm long; petiole spines extending along the margin of the first leaflet; costa 77 - 82 cm long; adaxial hastula conspicuous, to 1.5 cm, abaxial hastula rudimentary; lamina radius to 100 cm maximum, dense indumentum on the ribs of some immature leaves; leaflets 102 - 132, 4.2 - 7.9 cm wide, apices acute and entire or splitting longitudinally with age, shortest leaflet 68 - 83 cm long; leaf divided to 61 - 83 cm; commissural veins 10 - 14 per cm, leaf anatomy isolateral.

Morphology Reproductive morphology Inflorescences

Pistillate inflorescences spicate; flower-bearing portion 76 - 90 cm long with 7 - 15 flowers arranged spirally Staminate inflorescences branched to two orders, upper subtending branches terminating in 1 - 3 rachillae; rachillae green-brown and catkin-like, 30 - 44 cm long, 2.3 - 3.3 cm diameter, usually with a mamilliform apex; rachilla bracts form pits that contain a cincinnus of 8 - 12 staminate flowers.

Morphology Reproductive morphology Flowers

Staminate flowers 0.4- 0.7 cm long, exserted individually from the pits, bracteoles 0.8 x 0.5 cm; calyx 0.5 x 0.2 cm, shallowly divided into three sepals, petals 0.2 x 0.1 cm; stamens 6 with very short filaments, 0.02 x 0.04 cm, anthers, 0.14 x 0.1 cm; pistillode minute Pistillate flowers 3.5 x 3 cm, bracteoles 2 cm diam., sepals 2 x 2 cm and petals 1.5 x 1.5 cm

Morphology Reproductive morphology Flowers Pollen

Pollen monosulcate, elliptical, 46- 65 μm long, aperture 38 - 52 μm long, polar axis 42 - 54 μm long; tectum perforate, sparsely covered with supratectal gemmae

Morphology Reproductive morphology Fruits

Fruits massive, 25 - 35 x 7- 18.5 cm, ovoid with a somewhat pointed apex; fragrant and yellowish green at maturity; produced inside persistent perianth segments; pyrenes 1 - 2(- 3), 8.7- 12.1 cm x 8.3 -12.3 cm x 6.3 - 7.5 cm, unlobed or somewhat bilobed; some pyrenes with one or two external longitudinal furrows; internal flanges absent; an external, longitudinal crest is common.

Distribution

Endemic to Madagascar, where it is found in the dry western part of the island. Populations in Mahajanga Province are all in close proximity to human settlements. There appears to be no overlap with the range of B. aethiopum in the Sambirano region of northwest Madagascar.

Ecology

Riverine forest in low-lying areas, particularly on sandy or alluvial soils. Borassus madagascariensis does not form monospecific forest. It is common in several towns in the northwest of Madagascar, where it grows in gardens, streets and on waste ground.

Conservation

Vulnerable. Dransfield & Beentje (1995a) assessed B. madagascariensis as vulnerable (VU A1c) due to habitat loss and the encroachment of human settlements. Subsequent investigation by the author can only confirm this assessment. Of all the species of Borassus, this one has the smallest range. While the species does not appear to be threatened by over-exploitation, as are some populations of B. aethiopum in mainland Africa, all of the populations visited by the author were in close proximity to expanding human settlements. Some populations are actually confined to urban areas (Bayton et al. 2003) and the decline in habitat quality qualifies this species as vulnerable.

Vernacular

Dimaka (Sakalava). This name is also used for B. aethiopum in Madagascar.

Note

The case for continued recognition of this species has been difficult to assess. Most of the taxonomic accounts dealing with Borassus madagascariensis focus on differentiating it from the other Madagascar species, B. sambiranensis. Borassus madagascariensis has close affinities with B. aethiopum. This is not entirely unexpected as East Africa is the likely origin of the seeds that colonised Madagascar. Both species are generally large in all aspects, and both have a ventricose stem. The differences between the species are rather subtle and can be difficult to interpret in the herbarium. Borassus madagascariensis has small petiole spines that are like saw-teeth, while the spines of B. aethiopum are large and recurved. In B. madagascariensis, the petiole remains green along its entire length, in both high and low light environments. In B. aethiopum, the petiole is yellow and turns brown towards the stem. In juvenile specimens of B. aethiopum, the petioles are completely black (in full sun) or yellow-brown (shade). Juvenile specimens of B. madagascariensis have greenish-yellow petioles. The fruit apex of B. madagascariensis is pointed and in this respect, it is similar to that of Borassus akeassii. The fruit apex of B. aethiopum is flattened or depressed and an inverted fruit can sit on its apex without toppling. The fruits and seeds of B. madagascariensis are the largest in the genus. While the colour characters can be difficult to employ in the herbarium, the petiole spines are easily identifiable. In combination with the large fruits and seeds, and a known origin in Madagascar, this taxon should be easily identified. Jumelle and Perrier de la Bâthie (1907, 1913) did not cite a type specimen when describing B. madagascariensis, so a neotype has been selected. The neotype was collected in the town of Marovoay, at the head of the Bay of Bombetok, which corresponds to the locality cited by Bojer (1837: 308): "sur les bords de la rivière Marou-voai dans la baie de Bombetok". The epithet 'madagascaniensis' translates as 'of Madagascar'.

IUCN Red List of Threatened Species https://www.iucnredlist.org/species/38452/2869399

Conservation

EN - endangered