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Jatropha curcas is a native Mexican plant, distributed in the forests of coastal regions; it has shown potential for the production of biofuel, and its raw protein can be used as animal feed. Nevertheless, its current varieties have low yield and production variability, as it is in domestication period. The knowledge of the pollen grains is fundamental for studies of Jatropha reproductive biology and breeding for genetic improvement to generate new hybrids and improve fruit and seed yield. This study compared pollen morphology of four Jatropha species, which include two varieties of J. curcas (one toxic from India and one non-toxic from Mexico), and two varieties of wild J. cinerea (Sinaloa and Baja California Sur); additionally, pollen was collected from wild J. platyphylla (Sinaloa) and J. vernicosa (Baja California Sur) to characterize them palynologically. We used a scanning electron microscope to describe the size and shape of pollen grains. Pollen grains were observed spheroidal. The diameter of the varieties of toxic and non-toxic J. curcas and that of J. platyphylla were 58 ± 2.3, 54 ± 1.7, and 51 ± 2.4 μm, respectively; the number of clavae was 84 ± 10, 108 ± 15, and 180 ± 15.5, respectively. Pollen grains of J. cinerea (Sinaloa) had a diameter of 50 ± 1.7 μm and 220 ± 14 clavae by area; J. cinerea (Baja California Sur) had a diameter of 45 ± 1.9 μm and 195 ± 14.7 clavae. Pollen grains of J. vernicosa had a diameter of 46 ± 2.1 μm and 231 ± 25.6 clavae. The ornamentation of the exine showed clava with capita gemma shaped for varieties of J. curcas species and clavum shaped for J. platyphylla, J. cinerea and J. vernicosa species. The studied varieties have a cross-linked endexine and ectexine intectate. Luminal bacules were observed in the reticular space of J. curcas varieties while none were present in the varieties of J. cinerea, J. platyphylla, and J. vernicosa. [ABSTRACT FROM AUTHOR]

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To better understand the potential distribution of Taxus globosa Schlecht., we used a conifer species with restricted distribution, listed on the NOM-059-SEMARN AT-2010, a modeling distribution procedure of maximum entropy or MaxEnt, based on 40 occurrences of field records and 39 REMIB -CONABIO records. Two different scenarios of geographical and environmental coverages--climatic and topographic--were proved statistically. The BIOCLIM variables scenario with topography data show a more accurate model in the range of 0.9 to 1.0 probability with a 55% coincidence; it was statistically significant at (AUC=0.985). Slope variable indicates an environmental variable with more influence in potential modeling, followed by Bio14 (Precipitation of Driest Month). In agreement with the MaxEnt analysis with 19 BIOCLIM and 3 topographic variables, the main plant communities in the modeling area (where Taxus globosa is distributed in Mexico) are pine-oak forest, oak-pine forest, pine forest, and cloud mesic forest. Taxus globosa is potentially distributed in Hidalgo, Nuevo León, Puebla, Tamaulipas, and Veracruz. [ABSTRACT FROM AUTHOR]

The pedregal of Arocutin, with a surface area of approximately 31 km², is located in the Lake Patzcuaro basin, in the northern portion of the Mexican state of Michoacan. This region belongs to the Trans-Mexican Volcanic Belt physiographic province. The vegetation found is an oak forest in different stages of succesion, intermixed with elements of tropical deciduous forest. The structure and floristic composition of each association is described. Intense botanical exploration for a period of two years resulted in the collection of 407 species of vascular plants, belonging to 262 genera and 96 families; these represent 38.76% of the total number of species in the Lake Patzcuaro basin. The most diverse families are: Compositae with 60 species, Leguminosae with 27, La-biatae with 19, and Gramineae with 18. Comparing the floristic list of the pedregal of Arocutin with those of three other outcrops of basaltic rocks along the Trans-Mexican Volcanic Belt, using the Sbren-sen similarity index, we found that the Arocutin and Huaniqueo pedregals are the most closely related, both at generic and specific level. This is followed by the pedregal of San Angel in Mexico City and finally the pedregal of Chichinautzin, Morelos. Additionally, traditional uses of some plants are recorded. [ABSTRACT FROM AUTHOR]

We updated the floristic checklist of the Nizanda region, Isthmus of Tehuantepec (southern Mexico), characterized the occurring plant communities based on dominant species, and described the region’s flora according to life form, growth form, growth type, and growth habit spectra. Ten years of botanical exploration, along with surveys in 188 100-m2 samples from different vegetation types, provided the baseline floristic information. Ordination and classification analyses were performed to examine the degree of differentiation between communities. Geographical ranges of all species were used to assess biogeographical relationships of this flora. The inventory includes 920 species (553 genera, 124 families). More than one-third of the families were represented by a single species, whereas the 10 richest families had 43% of the species richness. Dendrograms showing plot classification at three taxonomic levels (species, genus and family) revealed savannah as the most strongly differentiated community amid seven vegetation types. Regarding growth forms, forbs and trees prevailed. Phanerophytes were the most common life form category, whereas herbs and woody plants were the dominant growth types. The largest richness for all taxonomic levels was recorded in the tropical dry forest. The expanded floristic knowledge gained for the Nizanda region provided better criteria to revise the classification scheme of its vegetation. Our preliminary biogeographical analysis illustrates the role of the Isthmus of Tehuantepec as a corridor for thermophilous floras between two oceanic watersheds, and as a natural distributional limit for several Mesoamerican plant species. [ABSTRACT FROM AUTHOR]

The tropical dry forest is an ecosystem under strong human pressure. It is found both inland and on coastal dunes. The objective of this research is to identify native tree and palm species growing on dunes that are used by local communities. In this research we carried out surveys and interviews among residents of San Isidro and Colonia La Mancha, in the coast of Veracruz on the use of trees of the tropical dry forest on dunes. Among the 55 registered species, Cedrela odorata, Diphysa robinioides, Enterolobium cyclocarpum, Bursera simaruba, Gliricidia sepium, Tabebuia rosea, Chrysobalanus icaco, Guazuma ulmifolia, Acacia cochliacantha, Brosimum alicastrum, Bumelia celastrina, Cocos nucifera, Maclura tinctoria, Piscidia piscipula, Spondias mombin and Ficus spp. were mentioned by more people. Eighteen uses were recorded, being the most frequent construction of houses (119 mentions), posts for fences and live fences (99), firewood (72) and food (48). Four of the uses mentioned refer to environmental services provided by these plants in the dunes. The species with higher number of uses is Gliricidia sepium and Bursera simaruba is the species in which more parts are used, followed by Gliricidia sepium, Guazuma ulmifolia and Brosimum alicastrum. We also inquired about the parts of the tree being used, the frequency, their sale and local price. Based on the results we suggest a group of species that can be used to increase species tree richness in the secondary growths and grassland on dunes, which will provide wood, forage, etc., to the local inhabitants and help maintain the tree cover of the dunes. [ABSTRACT FROM AUTHOR]

Aim The purpose of the study was to assess the degree of floristic differentiation between tropical dry forest (TDF) and savanna occurring in a single landscape. This comparison provides information on the responses of vegetation to the prevailing environmental conditions, while it also allows us to make inferences about large-scale events and processes, both biogeographical and evolutionary. Our approach included three levels of analysis: (1) taxonomic, (2) morphological and (3) vegetational. Location The seasonal dry tropical landscape in the Nizanda region, Oaxaca State, southern Mexico. The landscape comprises a complex vegetation mosaic in which tropical dry forest and savannas are the most conspicuous components. Methods Comparisons between TDF and savanna were based on inventories for these communities produced after 8 years of botanical survey. At the taxonomic level, the relative representation of taxa of different hierarchical levels in each community was examined. Morphological analyses required the classification of species on each of three criteria: (1) growth form, (2) life form and (3) growth habit. Vegetation level analysis was based on the frequencies of taxa in one hundred 100-m2 composition plots with which matrices of binary data were constructed for species, genera and families. These were subjected to classification analysis with Ward's method and using Euclidean distances as the dissimilarity algorithm. Results The combined flora for both communities comprised 600 species, 375 genera and 94 families; between them they shared 31, 40 and 34 taxa, respectively. The corresponding Sørensen similarity values were 10%, 21% and 72%, respectively. Ranking genera and families according to their species richness displayed large differences between savanna and TDF. Large differences between these communities were observed for Acanthaceae, Cactaceae, Euphorbiaceae and Mimosaceae, whereas Fabaceae and Asteraceae had similar high ranks according to the species richness in the two systems. The growth form spectrum diverged between the two communities, with TDF having more trees, shrubs and climbers. Savanna was characterised by forbs and graminoid herbs. Growth habit spectra revealed a clear dominance of herbaceous and suffruticose plants in savanna, and of woody elements and epiphytes in TDF. Regarding Raunkiaer's life forms, savanna had relatively more hemicryptophytes, and TDF more phanerophytes. Classification analyses showed that savanna and TDF forest samples kept their identities, regardless of taxonomic level (species, genera and families) at which the analyses were performed. Main conclusions The TDF and savanna of Nizanda represent two floristic systems with a large degree of differentiation at all taxonomic levels and patterns of morphological attributes. This suggest that the two floristic sets have evolved independently for extended periods of time, despite their close proximity. One important implication of this floristic differentiation is the large joint contribution made by these communities to the regional flora. [ABSTRACT FROM AUTHOR]

A successional role for each phytogeographical group of seral stands of the pine-oak forests in the Highlands of Chiapas (southern Mexico) could be established after their structural analysis. Most of the Holarctic elements regenerate in early successional conditions, while the regeneration of many Andean and East Asian elements is restricted to the more advanced stands. Forest structure and floristic composition appears as the result of a mixture of species belonging to genera of diverse origin. Their local coexistence seems to depend on their tolerance to those environmental conditions resulting from forest development through succession. We ascribe a central role to the canopy species belonging to Holarctic genera which determine the understory microhabitat for most of the remaining woody species, notably for those of Andean affinity. [ABSTRACT FROM AUTHOR]

The phenologies of trees with temperate and tropical historical phytogeographical affinities were recorded during 60 months (1990-- 1994)in a lower montane forest (1300 m a.s.l.) in Veracruz, Mexico. The objective was to determine phenological patterns and their relation toclimate for both deciduous and broadleaved-evergreen species. Leaf fall, leaf flush, flowering, and fruiting were recorded for 107 individuals belonging to twelve deciduous and twelve broadleaved-evergreen species. Phenological stages were scaled from 0 to 4 (referring to the proportion of each tree in a phenophase), and averaged monthly as aphenological index. Phenological periodicity was analysed as a nonmetric time-series using measures of predictability, constancy, and contingency. The climate is mild with a dry-cool season (November-- March), a dry-warm season (April--May), and a wet-warm season (June--October). Foliar phenological patterns differed between deciduous and evergreen species. Deciduous species dropped leaves during the dry-cool season and leaf drop was negatively correlated with minimum temperature; leaf flushing occurred during the dry-cool and dry-warm seasons and was positively correlated with maximum temperature. In general, broadleaved--evergreen species continually dropped and flushed leaves throughout the year. Flowering and fruiting patterns did not differ between leaf habits. Mean flowering peaks occurred between February andMay, but each individual species had a different annual peak. Fruiting occurred in the dry-warm and wet-warm seasons. Three species were distinct in their fruiting phenologies, Styrax and Meliosma exhibitedsupra-annual patterns, and Hedyosmum fruited most of the year. For several species, fruiting and minimum temperature were positively correlated. Factors other than abiotic ones (e.g. biotic interactions andphylogenetic relationships) may be involved in the phenological patterns observed and they should be investigated. [ABSTRACT FROM AUTHOR]