Robust, solitary, unarmed, pleonanthic, dioecious, tree palms. Stem erect, ringed with close leaf scars. Leaves induplicate, very briefly costapalmate, marcescent in immature individuals, neatly abscising under their own weight in mature trunked individuals; sheath becoming fibrous marginally, narrow, glabrous but tomentose abaxially along the margins, with a conspicuous triangular cleft below the petiole; petiole robust, covered with caducous indumentum, adaxially deeply channelled, abaxially rounded, the margins smooth, very hard and very sharp; adaxial hastula well developed, abaxial hastula absent; blade divided nearly to the insertion into compound segments, these further divided rather irregularly to 1/4–2/3 the radius into single-fold segments, in turn shallowly divided along the abaxial folds, interfold filaments persisting, the segment surfaces similar in colour or with white indumentum beneath, blade with bands of brown caducous scales, longitudinal veins and transverse veinlets prominent. Inflorescences interfoliar, strongly dimorphic, ± pendulous. Staminate inflorescence branched to 2 orders, with a short to long peduncle; prophyll large, 2-keeled, tubular near the base, inflated distally, splitting along much of its length, densely covered in caducous indumentum, tending to disintegrate at the tip and margins into fibres; peduncular bracts 1–few, like the prophyll but with a single keel; rachis shorter or longer than the peduncle; rachis bracts like the peduncular; first-order branches distant or crowded, bare, semicircular in cross-section, with sharp edges, short or long, bearing 1–5 robust catkin-like rachillae crowded at the tip, each subtended by a small triangular bract; rachillae close or diverging, bearing a tight spiral of large scaly or hairy, imbricate bracts, connate to each other laterally and adnate to the axis to form pits, each pit containing a cincinnus of 2–6 flowers, floral bracteoles spathulate. Staminate flowers exserted one at a time from the pit; calyx membranous, tubular, tipped with 3 short triangular lobes, most of the calyx remaining included within the pit; corolla with a long stalk-like base carrying the rest of the flower out of the pit, petals 3, ±imbricate, elongate; stamens 6–15 with very short filaments and elongate latrorse anthers; pistillode minute or absent. Pollen brevi-ellipsoidal to oblate-spheroidal, bi-symmetric; aperture a distal brevi-sulcus or a single large pore; ectexine tectate, coarsely foveolate or reticulate, aperture margin psilate; infratectum columellate; longest axis 60–85 µm [2/2]. Pistillate inflorescence unbranched or with up to 4 branches; prophyll, peduncular bracts and rachis bracts as in the staminate inflorescence, inflorescence axis, where unbranched, terminating in a rachilla, where branched, having rachillae borne singly at the tip of bare, flattened first-order branches as in the staminate inflorescence; rachillae short to long, bearing a spiral of large hairy, frequently notched, scaly, imbricate bracts, connate to each other and adnate to the axis to form shallow pits (Borassodendron machadonis) or almost free but closely overlapping (B. borneense), each subtending a solitary pistillate flower (or abortive flower), the rachilla tip frequently bearing sterile bracts, sometimes with an apparently terminal flower, the bract margins frequently erose. Pistillate flowers sessile, ± superficial or partially sunken in pits, each surrounded by 2 large ovate, irregularly margined bracteoles; sepals 3, distinct, ovate, imbricate, the margins ± notched; petals 3, distinct, ovate, similar to the sepals; staminodal ring short, with 6–9 teeth bearing minute empty anthers; gynoecium globose, trilocular, triovulate, tipped with 3 fleshy approximate stigmas, ovule form unknown. Fruit large (1–2)–3-seeded, stigmatic remains apical; epicarp smooth, mesocarp fibrous, the interfibre parenchyma becoming sweet, fragrant, and fleshy at maturity, endocarp comprising 3 separate pyrenes with thick stony walls, walls with 8–12 shallow internal, longitudinal ridges penetrating the seed. Seed grooved longitudinally by the pyrene ridges, endosperm homogeneous, with a slight central hollow; embryo apical. Germination remote-tubular; eophyll palmate with ca. 5 segments. Cytology not studied.
Borassodendron machadonis is a rare palm, sometimes found in areas of deep soil on limestone hills, sometimes on ridges in hill Dipterocarp forest. In Borneo, B. borneense can be locally abundant on hills in the lowlands but is absent from wide areas of apparently suitable forest. The young leaves of B. borneense are eaten by orangutan, which can cause considerable damage; the same animals may be responsible for dispersal.