Large, creeping, unarmed, pleonanthic, monoecious palm. Stem stout, prostrate or subterranean, branching dichotomously, curved leaf scars evident above, roots borne along the lower side. Leaves few, very large, erect, reduplicately pinnate; sheath soon splitting, glabrous; petiole stout, elongate, wide basally, channelled adaxially, terete distally, the base often persistent as a conical stub after the blade has disintegrated; rachis terete basally, becoming angled distally; leaflets numerous, single-fold, regularly arranged, acute, coriaceous, midrib prominent bearing distinctive, shining, chestnut-coloured, membranous ramenta abaxially, transverse veinlets not evident. Inflorescences solitary, interfoliar, erect, branching to 5(–6) orders, protogynous; peduncle terete; prophyll 2-keeled, tubular; peduncular bract tubular, somewhat inflated, pointed, rubbery, splitting longitudinally; rachis usually shorter than the peduncle, terete, terminating in a head of pistillate flowers and below this bearing 7–9 spirally arranged, closed, ± inflated, tubular bracts each subtending a first-order branch; first-order branches adnate ca. 1/2 their length above the subtending bracts, each bearing and enclosed by a tubular prophyll in bud; subsequent branches all bearing a complete, tubular, closed prophyll and ending in a short catkin-like rachilla, bearing densely crowded, spirally arranged, solitary staminate flowers, each subtended by a small bract. Staminate flowers sessile; sepals 3, distinct, narrow, oblanceolate; petals 3, distinct, slightly imbricate, similar to the sepals but slightly larger, both loosely closed over the stamens in bud; stamens 3, filaments and connectives connate in a solid stalk, anthers elongate, extrorse; pistillode lacking. Pollen spheroidal, bi-laterally symmetric; aperture a meridional zonasulcus; ectexine semi-tectate, finely reticulate with wide-based supratectal spines; infratectum columellate; diameter 37–80 µm; post-meiotic tetrads tetragonal [1/1]. Pistillate flowers very different from the staminate; sepals 3, distinct, irregularly oblanceolate, petals 3, similar to those of the staminate flower; staminodes lacking; carpels 3(–4), distinct, much longer than and obscuring the perianth at maturity, ± obovoid, asymmetrical, angled by mutual pressure, ± acute distally, and with a ± lateral, funnel-shaped stigmatic opening, ovule anatropous, attached dorsally or submarginally near the base of the locule. Fruit borne in ± globose head, fertile and partially developed fruits intermixed, 1–3 carpels per flower maturing a seed; fruit developing from 1 carpel, compressed and irregularly angled, stigmatic remains terminal, pyramidal; epicarp smooth, mesocarp fibrous, endocarp thick, composed of interwoven fibrous strands, with an adaxial internal longitudinal ridge intruded into the seed. Seed broadly ovoid, grooved adaxially, hilum basal, raphe branches ascending from the base, endosperm homogeneous or rarely ruminate, with a central hollow; embryo basal. Germination on the fruiting head with the plumule exserted and pushing the fruit away; eophyll bifid or with several leaflets. Cytology: 2n = 34.
Nypa is strictly a mangrove palm, occurring in a variety of estuarine situations; it usually grows in soft mud, often in vast natural stands. Pollination appears to be by drosophilid flies in New Guinea (Essig 1973), but Hoppe (2005) suggests a combination of pollination by various different insects and possibly also wind; correlations of pollination with floral anatomy and development have been noted (Uhl and Moore 1977a).
A single species, Nypa fruticans, occurring from Sri Lanka and the Ganges Delta to Australia, the Solomon Islands and the Ryukyu Islands. Introduced in the late 19th Century to the Niger Delta in West Africa, Nypa has now spread thence to western Cameroon. It has also been reported recently as naturalised in Panama (Duke 1991) and Trinidad (Bacon 2001), possibly having arrived from West Africa by ocean currents.
Nypa fruticans is ethnobotanically very important. The leaves are one of the most important sources for the production of palm shingles (‘atap’) for thatching, and also have minor uses such as for cigarette papers and fishing floats. The inflorescences are tapped for sap for sugar and alcohol production. The large natural stands of Nypa remain a greatly underexploited resource for fuel alcohol. The young endosperm is eaten, usually boiled in syrup, as a sweetmeat. The great but passive potential of Nypa as a stabiliser of estuarine mud in preventing coastal erosion should not be underestimated. For details of the utilisation of Nypa, see Burkill (1966), Brown and Merrill (1919) and Fong (1987, 1989).