We investigated the forest structure, leaf demography, leaf allometry and growth of the erect canopy of the mangrove palm Nypa fruticans in four river systems distributed over 10 degrees of latitude in the tropics of northeast Australia and Papua New Guinea to obtain estimates of aboveground biomass (AGB) and annual aboveground net primary production (ANPP). In the four river sites Nypa mean leaf and tree densities ranged from 6538 to 12,200 leaves ha−1, and 1526 to 3550 trees ha-1 and differed significantly among sites, with the lowest densities at the lowest latitude site. AGB ranged from 36.5 to 55.7 Mg ha−1 and also differed among sites with the lowest AGB at the lowest latitude site. The mean plastochron increased with increasing periods of cooler air temperatures. Mean litter production per tree (range, 6.0–16.2 kg year−1) was least in the low latitude site and mean total productivity per tree (range, 13.9–25.1 kg year−1) did not differ significantly across sites. ANPP was lowest in the low latitude site and ranged from 23.8 to 60.9 Mg ha−1 year−1. This placed Nypa forests in the mid to high range of global estimates of ANPP. Rates of litter production at three sites (range, 25.7–37.5 Mg ha−1 year−1) was much greater than for litterfall in any other mangrove forest. ANPP estimated using a combination of demographic data and leaf allometry compares well with previous estimates using a light interception method to predict productivity. The complex pattern of differences in forest structure, growth and ANPP across latitudes likely represent differences in catchment land use, successional stages of forests, river discharge and variation in the length of the dry season.