Borassus L.

Palmae, John Dransfield. Flora of Tropical East Africa. 1994

Morphology General Habit

Solitary, robust to massive, pleonanthic dioecious tree palms; stems sometimes ven-tricose, unbranched or branching due to injury

Morphology Leaves

Leaves massive palmate or costapal-mate, often long persisting but finally falling to leave a clean trunk; leaf-sheath short, not clearly distinct from the petiole, splitting longitudinally to produce a central triangular cleft; petiole stout, usually armed with irregularly curved and erose teeth along the margins, terminating in a conspicious adaxial hastula and a much smaller abaxial hastula; lamina divided into numerous induplicate usually bifid segments

Morphology Reproductive morphology Inflorescences

Inflorescences axillary, interfoliar, ♂ markedly differing from the ♀ Male inflorescence with an elongate peduncle bearing a prophyll and several bracts; partial inflorescences few-numerous, each borne in the axil of a rachis-bract, the branch-axis adnate to the main axis for some distance above the insertion; branch axis with a basal bare portion terminating in (1–)3 or more rachillae; rachillae massive, cylindrical, bearing connate imbricate bracts, also partly adnate to the axis to form pits, each enclosing a cincinnus of flowers and closed by the free tip of the bract; cincinus bearing 3 or more flowers Female inflorescence simple or with 1–2 branches, clothed in large imbricate and connate bracts

Morphology Reproductive morphology Flowers

Male flowers emerging one by one from the pits; sepals 3, connate into a shallowly or deeply lobed tube; corolla stalk-like at the base, lobes 3, imbricate; stamens 6, with subulate filaments and erect anthers; pistillode minute Female flowers massive, solitary, borne in the axils of these bracts, each subtended by 2 bracteoles; sepals 3, imbricate; petals 3, similar to the sepals; staminodes 6, forming a ring with minute anther rudiments; ovary globose, 3-locular, each locule with a single orthotropous ovule; stigmas 3, very short; septal nectaries conspicuous

sex Male

Male flowers emerging one by one from the pits; sepals 3, connate into a shallowly or deeply lobed tube; corolla stalk-like at the base, lobes 3, imbricate; stamens 6, with subulate filaments and erect anthers; pistillode minute Male inflorescence with an elongate peduncle bearing a prophyll and several bracts; partial inflorescences few-numerous, each borne in the axil of a rachis-bract, the branch-axis adnate to the main axis for some distance above the insertion; branch axis with a basal bare portion terminating in (1–)3 or more rachillae; rachillae massive, cylindrical, bearing connate imbricate bracts, also partly adnate to the axis to form pits, each enclosing a cincinnus of flowers and closed by the free tip of the bract; cincinus bearing 3 or more flowers

sex Female

Female flowers massive, solitary, borne in the axils of these bracts, each subtended by 2 bracteoles; sepals 3, imbricate; petals 3, similar to the sepals; staminodes 6, forming a ring with minute anther rudiments; ovary globose, 3-locular, each locule with a single orthotropous ovule; stigmas 3, very short; septal nectaries conspicuous Female inflorescence simple or with 1–2 branches, clothed in large imbricate and connate bracts

Morphology Reproductive morphology Fruits

Fruit massive, 1–3-seeded, borne within the persistent perianth-segments; epicarp usually smooth or cracked vertically; mesocarp fibrous and pulpy

Morphology Reproductive morphology Seeds

Germination remote tubular; eophyll simple. Seeds each enclosed in a separate endocarp; endosperm homogeneous with a central hollow; embryo apical

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

Type

Type species: B. flabellifer L.

Morphology General Habit

Massive, solitary, dioecious, pleonanthic tree palms

Morphology Stem

Stem grey with well-defined leaf scars, base often enlarged; stem ventricose with 1 to several swollen sections below the crown, or not ventricose; branching occasionally when damaged

Morphology Leaves

Leaves costapalmate, between 16 and 28 in the crown, remaining attached to the stem in juvenile specimens, then abscising cleanly in adulthood; leaf sheath short and indistinct from the petiole, splitting longitudinally to form a triangular cleft; petiole robust, armed or unarmed, petiole colour varying from green to yellow or black; adaxial hastula distinct at the junction of the petiole and lamina, rudimentary abaxial hastula present or absent; adaxial and abaxial indumentum on some juvenile leaves, confined to the ribs; leaflets induplicate, apices bifid or entire, acute or cuspidate; commissural veins noticeable, particularly in dried material, leaf anatomy isolateral or dorsiventral.

Morphology Reproductive morphology Inflorescences

Staminate inflorescences axillary, interfoliar and shorter than the leaves, branched to one or two orders, extended peduncle bearing a coriaceous bicarinate prophyll; peduncular bracts absent; rachis bracts yellow-green with green striae, lower rachis bracts similar to prophyll, partial inflorescences borne in the axil of rachis bracts, upper subtending branches terminating in 1 - 3(- 5) rachillae; rachillae green to brown and catkin-like, covered in imbricate scale like rachilla bracts, bracts forming pits containing a cincinnus of 6 or more staminate flowers. Pistillate inflorescences axillary, interfoliar, pendulous, either spicate or branched to one order; prophyll coriaceous with a hard acuminate apex; peduncle generally short, but sometimes extended with several empty bracts, similar in form to the prophyll; flower-bearing portion densely covered in large imbricate, cupular bracts

Morphology Reproductive morphology Flowers

Staminate flowers exserted from the pits in succession by elongation of the floral receptacle; flowers exserted individually or, rarely in groups, each subtended by membranous bracteoles; calyx membranous and shallowly or deeply divided into three sepals, corolla and receptacle fused for most of the length of the flower, distally with three free cucullate petal lobes; stamens 6 with very short filaments, fused to the receptacle, anthers erect, dorsifixed, latrorse; pistillode present, small or large Pistillate flowers large, solitary and superficial on the rachis; subtended by two large bracteoles; sepals (x 3) and petals (x 3) similar, coriaceous and imbricate; staminodal ring with 6 teeth usually present; ovary tricarpellate with basal locules and orthotropous ovules, surmounted by three stigmatic areas, septal nectaries basal.

Morphology Reproductive morphology Flowers Pollen

Pollen monosulcate and elliptical; longest axis in polar view (L) 46 - 95 μm, polar axis in equatorial view (h) 30 - 89 μm; aperture slightly shorter than the grain (37 - 95 μm)

Morphology Reproductive morphology Fruits

Fruits massive and fragrant; mature fruits may be yellow, orange, red, green or black, produced inside persistent perianth segments; epicarp coriaceous, mesocarp pulpy, filled with longitudinal fibres, endocarp woody and fibrous; pyrenes 1 - 3, pyrene length equalling breadth or much longer than wide, sometimes bilobed, some pyrenes have a prominent dorsal crest, while others have longitudinal furrows that can penetrate the seed; additional internal flanges sometimes present in B. heineanus

Morphology Reproductive morphology Seeds

Seed closely adhering to the endocarp, endosperm homogeneous and bony with a small central space; embryo apical.

Note

Germination remote tubular with a simple eophyll. n = 18 in B. flabellifer ( Read 1966; Rangasamy & Devasahayam 1971). There is minimal intra-specific variation in Borassus pollen and only B. akeassii deviates significantly from the norm. In that species, the tectum is reticulate and the supratectal gemmae densely cover the surface, all but obscuring the tectum. The differences between B. aethiopum and B. flabellifer noted by Ferguson et al. (1986) do not hold up to scrutiny when pollen from a larger sample of specimens is examined. The generic name Borassus was considered masculine by Linnaeus (1753) as evidenced by his use of the masculine epithet 'flabellier'. However, Beccari (1914) published several new names in the genus, including B. heinieanus, with feminine epithets ('B. heineana'). This error was corrected recently by Govaerts & Dransfield (2005), but uncorrected epithets are common in the literature.

Baker, W.J., Barfod, A.S., Cámara-Leret, R., Dowe, J.L., Heatubun, C.D., Petoe, P., Turner, J.H., Zona, S. & Dransfield, J. (2024) Palms of New Guinea. Royal Botanic Gardens, Kew, Richmond. 726 pp.

Morphology General Habit

Robust, single-stemmed tree fan palm, dioecious

Morphology Leaves

Leaf palmate; sheath splitting to the base opposite the petiole; petiole robust, with sharp edges, with a conspicuous triangular cleft at the base; segments numerous, the blade split to ca. one third or more of its radius, with pointed tips

Morphology Reproductive morphology Inflorescences

Inflorescence among the leaves, the male inflorescence branched to 2 orders, the female inflorescence unbranched or with a single branch near the base, pendulous; prophyll and peduncular bract similar, not dropping off as inflorescence expands; peduncle longer than inflorescence rachis; rachilla very robust

Morphology Reproductive morphology Flowers

Flowers male flowers in groups developing in pits hidden by overlapping bracts on a thick sausage-like rachilla, emerging one at a time, female flowers borne singly, very much larger, surrounded by overlapping rounded bracts

Morphology Reproductive morphology Fruits

Fruit large, black, stigmatic remains apical, flesh yellow, fibrous

Morphology Reproductive morphology Seeds

Seeds 1–3, each inside its own endocarp, endosperm homogeneous.

Distribution

Six species in Africa, Madagascar, India to New Guinea, one known species in northern mainland New Guinea.

Note

Borassus is a genus of massive, single-stemmed, dioecious fan palms. The petiole of Borassus has a distinctive triangular cleft at the base and the fruit are very large. According to the latest monograph (Bayton 2007), there are six species globally, but only one, B. heineanus, occurs in New Guinea. It is most easily confused with Corypha, which is distinguished by its production of inflorescences above the leaves, stems that die after flowering, spiny petioles and smaller fruit. Other fan palms in New Guinea (Livistona, Saribus and Licuala) do not have the basal triangular cleft to the petiole.

Morphology

Leaf (Tomlinson 1961), root (Seubert 1997).

Distribution

Six species have been recognised. They occur in Africa, Madagascar, north-eastern Arabia, through India and Southeast Asia to New Guinea and Australia. Borassus is one of the most widespread palm genera.

Vernacular

Toddy or wine palm, lontar, palmyra, or siwalan (Borassus flabellifer).

Biology

Borassus flabellifer can occur in some mountain districts of India at elevations of 500–800 m, and is also found on banks of rivers. It is most abundant, however, on low sandy plains near sea level where exposed to sun and winds. In Africa, B. aethiopum occurs in open secondary forest and savannah.

Diagnostic

Large dioecious tree fan palms of Africa, Madagascar, the Indian Subcontinent and Southeast Asia, and the drier parts of Malesia; distinctive in the leaves with spiny petiole margins, the spines often very irregularly shaped, and large fruit with the endocarp usually lacking internal flanges that penetrate the homogeneous endosperm.

General Description

Tall, robust, solitary, armed, pleonanthic, dioecious, tree palms. Stem massive, covered in a lattice of leaf bases abscising cleanly in older specimens, then rough, ringed with wide leaf scars. Leaves induplicate, strongly costapalmate; sheath open early in development, later with a wide triangular cleft at the base of the petiole; petiole deeply channelled adaxially, rounded abaxially, surfaces smooth to minutely rough, margins of sheath and petiole armed with coarse irregular teeth; adaxial hastula conspicuous, triangular or scalloped, abaxial hastula a low ridge (?always); blade suborbicular to flabellate, divided along adaxial folds to ca. 1/2 its length into regular, stiff single-fold segments, these shortly bifid, interfold filaments present or absent, surfaces smooth, ramenta or tomentum along abaxial costa and ridges of folds, midribs prominent abaxially, transverse veinlets conspicuous, short, numerous. Inflorescences interfoliar, shorter than the leaves, the staminate and pistillate dissimilar. Staminate inflorescence branched to 2 orders; peduncle very short; prophyll 2-keeled, with long tubular base, limb short, pointed, variously split apically; (?)peduncular bracts lacking; rachis also short, rachis bracts similar to the prophyll; first-order branches long, flattened, each bearing a prophyll and branched digitately into several (1–3) rachillae; rachillae large, catkin-like, elongate, bearing spirally arranged, imbricate bracts, connate laterally and distally to form large pits, each containing a reflexed cincinnus of ca. 30 staminate flowers, exserted singly in succession from the pit mouth. Staminate flowers each subtended by a long membranous bracteole; sepals 3, asymmetrical, connate only basally or to 2/3 their length, distinct lobes keeled, elongate, membranous, stiff; corolla with a long stalk-like base and 3 short, rounded lobes, ridged adaxially; stamens 6, filaments short, triangular, anthers medifixed, elongate, latrorse; pistillode small, conical. Pollen ellipsoidal, bi-symmetric; aperture a distal sulcus; ectexine tectate, reticulate or finely perforate-rugulate, rarely foveolate-reticulate, with psilate supratectal gemmae, aperture margin similar but often without supratectal gemmae; infratectum columellate; longest axis 42–85 µm [2/6]. Pistillate inflorescence unbranched or with a single first-order branch; peduncle short; prophyll tubular, pointed, 2-keeled, split ventrally about 1/2 its length; peduncular bracts few (2 or more), if present as long as or longer than the peduncle; rachilla massive, bearing large cupular bracts, the first few empty, the subsequent each subtending a single pistillate flower, several empty bracts above the flowers. Pistillate flowers large, each bearing 2 lateral cup-like, rounded, leathery, bracteoles; sepals 3 distinct, imbricate, thick, rounded; petals 3, similar to sepals; staminodes triangular, connate basally in a low cupule, sterile anthers present or not; gynoecium rounded, tricarpellate, with a central, basal septal nectary, stylar region hemispherical, stigma a low knob, carpels each with a basal, orthotropous ovule, and 2 lateral bodies, perhaps vestigial ovules. Fruit large, rounded, sometimes wider than long, bearing 1–3 seeds, stigmatic remains apical, perianth enlarged, persistent; epicarp smooth, mesocarp thick, fibrous, often fragrant, endocarp comprising 3 hard bony pyrenes. Seed shallowly to deeply bilobed, pointed, basally attached, endosperm homogeneous with a central hollow; embryo apical. Germination remote-tubular; eophyll undivided, elliptical. Cytology: 2n = 36.