Mimosa Bimucronata Research Articles

The cytological origin of the polyads and their significance in the reproductive biology of Mimosa bimucronata

The mechanism of polyad formation in Mimosa bimucronata (DC.) Kuntze is described and its significance in the reproductive biology is discussed. In this species c. 500 complexes of two coupled pollen mother cells (PMCs) per pollen sac are formed after the last mitotic division of the sporogenous tissue. All the pollen grains of each complex remain attached and form a bitetrad. This mechanism leads to the formation of many polyads per pollen sac. On this basis, we propose that in Mimosa the number of pollen grains per polyad (eight or 16) is determined by the number of cells that remain attached after the last mitotic divisions of the sporogenous tissue. Concerning the biological significance of the polyads in M. bimucronata, we find that the number of pollen grains per polyad is correlated with the number of ovules per ovary, and that the internal dimensions of the pit-shaped stigma are sufficient just for one polyad to be localized in it. Based on the number of polyads per flower this species has a high pollen/ovule ratio characteristic of xenogamous plants, in opposition to that expected for plants with composite pollen dispersal units. In contrast, it has low pollination efficiency, low fruit set, a 1/1 relationship between the pollen grains of a polyad and the number of ovules per ovary, and high seed set per fruit. These facts support the hypothesis that the occurrence of polyads in M. bimucronata would be an adaptation helping to ensure high seed set following a single cross pollination event.

Phytosociology of the remaining xerophytic woodland associated to an environmental gradient at the banks of the São Francisco river - Petrolina, Pernambuco, Brazil

Floristic and phytosociological surveys were carried out for 12 months in the Embrapa-SPSB, Petrolina, Pernambuco, Brazil. A transect was laid on starting at the river bank extending for 790 m away from the river and divided into 140 10 × 10 m contiguous plots. In each plot, all standing plants, alive or dead, with stem diameter at soil level > 3 cm and total height > 1 m were sampled. Along this transect, an elevation range of 9.40 m was registered and five topographical environments were identified: riverside (MR), dike (D), floodable depression (DI), boundary terrace (TL) - all of them belonging to the fluvial terrace with Fluvic Neosol and Haplic Cambisol both silty textured eutrophic soils - and the inlander tableland (TS), with medium sandy-textured Red-Yellow Argisols. Fourty-eight species/morphospecies, distributed into 39 genera and 21 families, were identified. Four phytogeoenvironments (MR, D + TL, DI + TL, and TS) were registered based on environmental variations and floristic similarities among plots using cluster analyses. The MR environment showed the largest total density, total basal area, maximum and medium heights and maximum diameter. Moreover, it had 8.1% of plants with heights above 8 m against 0.6% for D + TL, 0.2% for DI + TL, and 0% for TS. The species with the largest importance value were Inga vera subsp. affinis (DC.) T.D. Pennington in MR, Mimosa bimucronata Kunth in D + TL and DI + TL and M. tenuiflora (Willd.) Poir. in TS.

Anatomia da madeira e casca do maricá, <i>Mimosa bimucronata</i> (DC.) O. Kuntze.

São descritos os caracteres gerais, macroscópicos e microscópicos da madeira de Mimosa bimucronata (DC.) O. Kutze, bem como a estrutura de sua casca. A anatomia da madeira é comparada com referências da literatura para espécies afins. Os caracteres observados incluem placa de perfuração simples em vasos, pontuados alternos, pontuações ornamentadas, parênquima paratraqueal, fibras libriformes, raios homogêneos de células procumbentes e ausência de estratificação. Na estrutura da casca destacam-se o líber duro em faixas tangenciais descontínuas, envolvidas por células parenquimáticas geralmente cristalíferas, o curso irregular dos raios na casca interna e a formação de cunhas de parênquima na casca mediana.

Water-soluble galactomannans from seeds of Mimosaceae spp.

The characterization of four galactomannans from the seeds of Mimosaceae spp., from natural Southern Brazilian sources having similar chemical structures with Man:Gal ∼ 1, was performed. 13CNMR spectra gave clear information on the chemical structure of these highly branched galactomannans. Their physico-chemical macromolecular characteristics were determined from SEC experiments, leading to the determination of parameters relating R G and [η] with M W. Applying a model of worm-like chain, a persistence length of L p ∼ 100 A ̊ was determined. The specific viscosity at zero shear rate was investigated, and demonstrated that a unique curve relates η sp with the overlap parameter C[η]; in the range of higher values of C[η], the slope was n = 6.2; the critical concentration c∗[η] = 1.9. Considering the structure and rheological properties, galactomannan from Mimosa flocculosa and Mimosa bimucronata might be potentially applied as thickeners in food and cosmetic products, as well as galactomannan from Mimosa scabrella Benthan, previously analysed.

Melissopalynological data obtained from a mangrove area near to Rio de Janeiro, Brazil

SUMMARYWe performed palynological analyses of honey and pollen samples from Apis mellifera situated in a mangrove belt in Guanabara Bay, state of Rio de Janeiro, Brazil. Laguncularia racemosa is the most abundant species in this area; some individuals of Avicennia tomentosa also occur. Pollen analysis showed that the bees visited ruderal plant species, grasses and crops for pollen. We recognized 27 pollen types that belong to 22 plant families. The most frequent pollen types from polliniferous species belong to Asteraceae, Euphorbiaceae, Fabaceae, Myrtaceae and Arecaceae. The most frequent pollen types from nectariferous species were Croton sp., Eucalyptus sp., Eupatorium maximilianii, Gochnatia polymorpha, Mimosa bimucronata, Mimosa pudica, Spondias sp. and Sapindaceae. Pollen from typical mangrove vegetation, except Laguncularia racemosa, was rare in both honey and pollen samples. This fact reflects the local environmental disturbance, as well as the value of the ‘invader’ plant species to bees.