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.
Solitary, robust to massive, pleonanthic dioecious tree palms; stems sometimes ven-tricose, unbranched or branching due to injury. 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. 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. 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 inflorescence simple or with 1–2 branches, clothed in large imbricate and connate bracts. 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. Fruit massive, 1–3-seeded, borne within the persistent perianth-segments; epicarp usually smooth or cracked vertically; mesocarp fibrous and pulpy. Seeds each enclosed in a separate endocarp; endosperm homogeneous with a central hollow; embryo apical. Germination remote tubular; eophyll simple.
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.
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.
Sp. Pl.: 1187 (1753) & Gen. Pl., ed. 5: 494 (1754); Becc. in Palme Borass.: 2 (1924)