Morphology, germination, and geographic distribution of Pentaclethra macroloba (Fabaceae): a hyperdominant Amazonian tree / Morfología, germinación y distribución geográfica de Pentaclethra macroloba (Fabaceae): árbol amazónico hiperdominante

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.

Introducción: Pentaclethra macroloba es un árbol hiperdominante en el estuario del Amazonas, de gran importancia socioeconómica para la región, pues el aceite de sus semillas es un poderoso medicamento natural. Objetivo: Nuestro objetivo fue caracterizar la estructura morfológica, las adaptaciones morfológicas en respuesta a las inundaciones diarias del estuario del Amazonas y el área biogeográfica de P. macroloba. Métodos: Una descripción detallada de la morfología externa, desde la germinación hasta el árbol adulto, se obtuvo de individuos ubicados en el bosque periódicamente inundado, al noreste de la Amazonia. El área de ocupación y la extensión geográfica de P. macroloba se determinaron a partir del punto de coordenadas geográficas de muestras botánicas depositadas en las colecciones digitales de Mobot y SpeciesLink. Resultados: Los individuos adultos tienen estructuras adaptadas en respuesta a las inundaciones diarias, tales como: raíces adventicias para aumentar la eficiencia respiratoria y lenticelas en el tronco, que sirven como punto de conexión para el transporte de oxígeno entre la raíz y la parte aérea. Los frutos secos favorecen la activación del mecanismo de dehiscencia explosiva, permitiendo que la semilla sea expulsada a larga distancia. La forma deltoidea de la semilla permite la fluctuación en el agua y una dispersión más eficiente. La plántula es hipogel fanerocotiledones y con un par de cotiledones de reserva que proporcionan a la plántula una fuente extra de energía para escapar de la inundación. La tasa de germinación fue del 78 % y la velocidad fue de 0.2 semillas día-1. El método Circular buffer reveló la presencia de 123 subpoblaciones de P. macroloba distribuidas en un radio de 5 699 943 km² a lo largo de la región neotropical. Conclusiones: Gran parte de las estructuras morfológicas de P. macroloba son respuestas adaptativas y evolutivas al ambiente periódicamente inundado del estuario del Amazonas, lo que demuestra que estos ambientes actúan como filtro ambiental seleccionado las especies mejor adaptadas al medio. Su amplia área geográfica denota la plasticidad de adaptarse a diferentes ambientes, lo que puede justificar su monodominancia en algunas regiones.

Postponing the production of ant domatia as a strategy promoting an escape from flooding in an Amazonian myrmecophyte.

Background and Aims: Even when adapted to flooding environments, the spatial distribution, growing strategies and anti-herbivore defences of plants face stressful conditions. Here we describe the effects of flooding on carbon allocation on growth, domatia and leaf production, and the herbivory on the myrmecophyte domatia-bearing Tococa coronata Benth. (Melastomataceae) growing along river banks in the Amazon region. Methods: In an area of 80 000 m2 of riparian forest along the Juruena River we actively searched for individuals of T. coronata. In each plant we evaluated the size of the plant when producing the first domatium and determined its best predictor: (1) plant total height; (2) size of plants above flood level; or (3) length of time each plant spent underwater. We also compared the herbivory, internode elongation, foliar asymmetry and specific leaf weight between T. coronata individuals growing above and below the maximum flooding level. The distance to the river and the height of the first domatium produced were compared between T. coronata and its sympatric congener, T. bulifera. Key Results: We found that T. coronata invests in rapid growth in the early ontogenetic stages through an elongation of internodes rather than in constitutive anti-herbivore defences to leaves or domatia to exceed the maximum flooding level. Consequently, its leaf herbivory was higher when compared with those produced above the flooding level. Individuals with leaves above flood levels produce coriaceous leaves and ant-domatias. Thus, flooding seems to trigger changes in growth strategies of the species. Furthermore, T. coronata occurs within the flood level, whereas its congener T. bullifera invariably occurs at sites unreachable by floods. Conclusion: Even in conditions of high stress, T. coronata presents both physiological and adaptive strategies that allow for colonization and establishment within flooded regions. These mechanisms involve an extreme trade-off of postponing adult plant characteristics to rapid growth to escape flooding while minimizing carbon allocation to defence.

Hyperdominance in the Amazonian tree flora.

The vast extent of the Amazon Basin has historically restricted the study of its tree communities to the local and regional scales. Here, we provide empirical data on the commonness, rarity, and richness of lowland tree species across the entire Amazon Basin and Guiana Shield (Amazonia), collected in 1170 tree plots in all major forest types. Extrapolations suggest that Amazonia harbors roughly 16,000 tree species, of which just 227 (1.4%) account for half of all trees. Most of these are habitat specialists and only dominant in one or two regions of the basin. We discuss some implications of the finding that a small group of species--less diverse than the North American tree flora--accounts for half of the world's most diverse tree community.