Introduction: Pentaclethra macroloba is a hyperdominant tree in the Amazon estuary of great socioeconomic importance for the region because the oil from its seeds is a powerful herbal medicine. Objective: We aimed to characterize the morphological structure, the morphological adaptations in response to the daily flooding of the Amazon estuary and the biogeographic area of P. macroloba. Methods: Detailed description of the external morphology, from germination to the adult tree, was obtained from individuals located in floodplain forest, Northeast Amazonia. The occupation area and the geographical extension of P. macroloba were determined from point of geographical coordinates of botanical samples deposited in the digital collections of Mobot and SpeciesLink. Results: Adult individuals have adapted structures in response to daily flooding, such as: adventitious roots to increase respiratory efficiency and lenticels in the trunk, serving as a connection point for oxygen transport between the root and the aerial part. Dried fruit favours the activation of the explosive dehiscence mechanism, allowing the seed to be expelled long distance. Deltoid shape of the seed allows water fluctuation and more efficient dispersal. Seedling is phanerocotylar hypogeal and with one pair of reserve cotyledons that provide the seedling an extra source of energy to escape the flood. Germination rate was 78 % and the speed was 0.2 seeds.day-1. Circular buffer method revealed the presence of 123 subpopulations of P. macroloba distributed in a radius of 5 699 943 km² across the Neotropical region. Conclusions: Much of the morphological structures of P. macroloba are adaptive and evolutionary responses to the periodically flooded environment of the Amazon estuary, showing that these environments select the trees, best adapted, to inhabit the flood. P. macroloba has a wide geographical area denotes the plasticity of adapting to different environments, which may justify its monodominance in some regions.

We analyzed the spatial distribution pattern of Pentaclethra macroloba to assist in the development of management plans and conservation of this species in estuarine floodplain forests. The study was conducted in an area of floodplain forest of 55.94 ha, in Mazagão, Amapá, Brazil. A census was performed and all individuals of ≥ 30 cm circumference at breast height (CBH), living and dead, were georeferenced. Ripley’s K function was used to analyze the spatial distribution of the population, including mortality and diameter classes. The relationships between distance to the edge of inundation and density and basal area of the population were analyzed using linear regression. We recorded 993 live individuals and 22 dead. The distribution of the population was found to vary with the topographic gradient associated with the distance to the edge of the inundation. Diameter classes 1 (≤ 13.2 cm) and 2 (≤ 18.6 cm) were spatially aggregated close to the water and randomly distributed far from the water. Classes 3 (≤ 24.0 cm) and 4 (≤ 29.5 cm) were aggregated at all distances, and classes 5 (≤ 34.9 cm), 6 (≤ 40.3 cm), 7 (≤ 45.7 cm) and 8 (≤ 51.2 cm), were randomly distributed at all distances. Mortality was randomly distributed. The population density was 18 trees h^-1 with a basal area of 49 m² h^-1, and both density (r²=0.51; p=0.0195) and basal area (r²=0.67; p=0.0039) increased with the distance from the edge of the inundation. We conclude that the spatial distribution and successful establishment of this species in floodplain forest are related to the dynamics of flooding and the resultant impacts on dispersal processes.

O estudo teve como objetivo realizar um diagnóstico quali-quantitativo da arborização da praça Floriano Peixoto, na cidade de Macapá-AP. Foram mensurados as CAP's e as alturas das árvores e das palmeiras, e determinados os parâmetros fitossociológicos, distribuição diamétrica e classes de altura da composição florística. As espécies ornamentais foram identificadas. Foram encontrados 240 indivíduos (palmeiras e árvores), distribuídos em 10 famílias, 18 gêneros e 19 espécies. As famílias que se destacaram com maior número de espécies foram Arecaceae e Fabaceae com quatro espécies cada. Euterpe oleracea Mart. dominou em número de indivíduos (86 indivíduos). As espécies que obtiveram maior índice de valor de cobertura foram: Clitoria fairchildiana R.A. Howard (46,35%), Mangifera indica L. (39,20%) e Euterpe oleracea (36,94%). O índice de diversidade (H') obtido foi 0,98. A estrutura diamétrica apresenta conformação de "J invertido". A maioria dos indivíduos, árvores e palmeiras, apresentam altura acima de 6 m. Foram encontradas nove famílias de espécies ornamentais, divididas em 11 gêneros e 12 espécies, sendo maioria exóticas. Os resultados sugerem medidas que visem o planejamento adequado da diversificação florística e valorização da flora local na arborização da Praça Floriano Peixoto. Essas medidas podem ser adotadas para outras praças de Macapá.