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Question: Understanding the specific distribution patterns of vascular plants on different spatial scales is central in ecology and conservation. We evaluate the distribution patterns of five plant life forms (climbers, epiphytes, herbs, shrubs, and trees) along the elevation gradient and geographic space of a mountain system, analyzing climate, topography, and human disturbance to explain variation in the richness of each life form, and determine the contribution of each life form to total richness along the elevation gradient. Location: Sierra Madre of Chiapas, southeastern Mexico. Methods: We used linear models to evaluate the elevational pattern of richness for each life form, as well as total richness, and analyzed the effects of climate (water–energy dynamics, thermal range), topography (topographic heterogeneity), and disturbance (Human Influence Index) on variation in total richness as well as of each life form using Generalized Linear Models (GLM). We used Non‐Metric Multidimensional (Distance) Scaling to determine variation in species composition along the elevation gradient. Finally, the contribution of each life form to total richness was evaluated using GLM. Results: We recorded 235 families, 1,439 genera, and 5,196 species. Total richness and the richness of each life form increased with increasing elevation. GLM explained a high proportion of the variation in the richness of each life form (34.3% for total richness; climbers 17.2%, epiphytes 44.9%, herbs 20.4%, shrubs 33.5%, and trees 24.9%). The proportion of richness of herbs and trees to total richness decreased, and the proportion of shrubs, epiphytes, and climbers increased with elevation. Climate largely determined species richness for all life forms, whereas disturbance was significant only for epiphyte richness. Conclusions: Results suggest that mechanisms driven by climatic variables (especially thermal range) contribute to maintaining the richness of each life form. However, human disturbance modifies distribution patterns and leads to a decrease in epiphyte richness. The differential contribution of each life form to total richness along the elevation gradient presents a challenge for designing conservation strategies applicable to all plant groups. [ABSTRACT FROM AUTHOR]

As currently defined, the 24 species of Schoenocaulon occur in three disjunct areas: north central Florida (one species, S. dubium), southern Peru (portion of the range of S. officinale), and the region from southeastern New Mexico-Texas south to Venezuela; the 20 species endemic to Mexico are geographically restricted. Species delimitations, often based on tepal morphology, have been problematic. Our analyses of ITS sequence data for all 27 species and infraspecific taxa support recognition of two new species and recircumscription and placement of elements of the polyphyletic S. ghieshreghtii and S. mortonii complexes. For taxa with adequate sampling, our data also indicate 11-12 cladospecies and 3-6 metaspecies according to the apomorphic species concept. The resolved phylogeny, correlated with geography and morphology, allows insight into biogeographical diversification and the evolution of some unusual morphological characters within the genus, such as nectary differentiation and tepal margin type. [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]

The genus Ceratozamia contains more than 20 species distributed in eastern and southern Mexico, with extensions into Central America. Morphology, anatomy, and molecular (ITS) data allow resolution of some aspects of species relationships, provide correlations with ecology, and suggest phytogeographic hypotheses. Some species complexes, such as those centered around C. norstogii and C. miqueliana, are restricted to southernwest Mexico, in what are regarded as Pleistocene floristic refugia. The low level of divergence of ITS sequences among taxa to the north of the Trans-Mexican Neovolcanic mountain range suggests a pattern of recent, and perhaps rapid, speciation. [ABSTRACT FROM AUTHOR]

Presents a study that identified an assemblage of leaves and leaflets under five species of the genus family of Anacardiaceae collected from the Oligocene Los Ahuehuetes locality of Puebla, Mexico. Description of the species; Biogeographic relationships; Synecological relationships.

Population size distributions were examined for 12 species of trees co-occurring at Chamela Biological Station in Jalisco, Mexico. Species had been selected as congeneric pairs and trios similar in gross morphology and ecology in order better to identify correlates of relative abundance. Rarer species were found unanimously to have more irregular distributions of individuals among size classes than more common species when distributions were compared to a smooth, descending curve constructed from population mean stem diameters (an exponential distribution). Examination among species of patterns of deviation from these corresponding smooth distributions indicates that the most reasonably inferred cause for the observed pattern is consistent differences in degree of fluctuation in recruitment into adult size classes. These results thereby suggest a demographic difference between locally rarer and more common species that may be generally associated with observed differences in relative abundance and indicate a focus for management of rarity in forest trees. [ABSTRACT FROM AUTHOR]

Aim The floristic affinities between Cuba and the Yucatán Peninsula are of great interest for plant geography and preservation of biodiversity in the Caribbean region. Although many authors have stressed the relationship between these regions, the conclusions are based mostly on general descriptive studies. Here we present a quantitative analysis in order to determine their floristic affinities. Location We compared the Mexican portion of the Yucatán Peninsula (states of Campeche, Yucatán and Quintana Roo) and several karst areas of the Cuban Archipelago; which were selected because of the great physiographic, climatic and vegetational similarities. Methods Data obtained from specialized references were used to create a taxonomic data base, this was complemented with a data base (D-BASE) that included data from herbarium specimens. Geographical information was obtained and adapted for use in a numerical taxonomy and multivariate system program (NTSYS). Using the latter, we performed a floristic affinity analysis using a monothetic method based on the comparison of the presence and absence of species. Floristic similarity was obtained using the Jaccard index of similarity and a dendrogram was created. Results Of a total of 1936 species, 880 were common to both Yucatán and Cuba; most being herbaceous species, followed by trees and bushes. The flora of Mexican island of Cozumel exhibited the lowest coefficient of similarity (11%) when compared with the rest of the sites considered. The second level in the dendrogram shows the branching of two large groups: the three states of the Yucatán Peninsula and the coastal areas of Cuba, and the Cuban interior. Highest similarity (73%) within the Cuban areas considered was obtained between the Isla de la Juventud and the Guanahacabibes peninsula; both areas also showed the highest floristic similarity with the Yucatán Peninsula (67%). The Cuban keys and the coastal plain of Tunas form a second group of Cuban localities that exhibited a relatively high floristic affinity with the Yucatán Peninsula. The areas of Maisí, Morrillo and Chico, in east Cuba, form a group with considerably high similarity (50%), and are physically the closest to Yucatán after the Coco–Romano–Caguanes group. The Cuban areas below 600 m in elevation were the least similar to the Yucatán Peninsula. Main conclusions Despite earlier suggestions, there are various areas of Cuba that have close floristic affinity with the Yucatán Peninsula, sometimes based on the presence of specific taxa, and other times based on large groups of taxa common to both study areas with different and broader types of distribution. The number of species (880) common to both the Yucatán Peninsula and the different karst areas of the Cuban Archipielago surpasses all expectations, as the native flora of the Yucatán Peninsula is estimated to have at least 1777 species, and if we exclude exotic, introduced and cultivated species, the general floristic similarity between Cuba and the Peninsula of Yucatán should be about 50%. [ABSTRACT FROM AUTHOR]

A track analysis based on the distributional patterns of 967 species of vascular plant taxa (gymnosperms, angiosperms and pteridophytes) was performed to assess conservation priorities for cloud forests in the state of Hidalgo, Mexico, ranged in the municipalities of Chapulhuac´m, Eloxochitl´m, Molocotl´m, Pisaflores, Tenango de Doria, Tlahuelompa and Tlanchinol, as well as five floristically equivalent areas in the states of Veracruz (Teocelo and Helechales), Tamaulipas (Gómez Farías), Morelos-México (Ocuilan) and Oaxaca (Huautla de Jiménez). In order to detect generalized tracks we employed a new parsimony method, where clades (considered equivalent to generalized tracks) are defined forbidding homoplasy and acting like a compatibility algorithm. Several generalized tracks were found connecting these areas. Cloud forests of Chapulhuacán were connected according to three different generalized tracks and thus have a higher value, qualifying as a priority area for the conservation of cloud forests in the state of Hidalgo. [ABSTRACT FROM AUTHOR]

The article presents a study on the mangrove ecology and the deltaic geomorphology specifically in some areas off Tabasco in Mexico. It highlights the significance of physiographic-ecological relationship in alluvial coasts. Coastal plant distribution and geomorphic processes were recorded along with the extent of vegetation communities and landform units. Mangroves along the Grijalva-Usumacinta Delta in Tabasco and Campeche in Mexico were the subject of this investigation. Information were observed on distribution, relation to landforms, and the dynamic ecology in response to changes in geomorphology.

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]