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A new species of Cedrela (Meliaceae) is described and illustrated from recently discovered populations at Rancho del Cielo Biosphere Reserve, Tamaulipas, Mexico. The newly proposed species is morphologically close to C. monroana but differs from the latter in having a shorter habit, thinner terminal twigs, shorter space between leaf pairs along the rachis, shorter petiolules, smaller leaflets, smaller leaflet length-to-width ratio, less numerous secondary leaflet veins, shorter panicles, and yellowish green flowers, broadly obovoid to pyriform fruits, with valves opening at least at an angle of 20 degrees and brown mature capsules with prominent lenticels on valves. We provide a key to the Mexican species of Cedrela including the closely related C. monroana . Latitudinal differences also support the setting aside of the proposed species, which is the most septentrional among its close relatives within Cedrela . Bayesian inference and maximum likelihood analyses of nuclear (ITS) and chloroplast ( accD , matK , rbcL , trnH-psbA , psbB-T-N , rpl16 , rpoB , rpoC1 , trnS-G ) DNA sequences of 19 taxa of Cedrela plus 3 from related taxa, place the proposed new species within a clade including Mexican & Central American species. Based on morphological and phylogenetic evidence, we propose the reinstatement of C. saxatilis as a valid species, previously treated as a synonym of C. oaxacensis .

Gradient analysis was used to determine factors driving small-scale variation of cloud forest communities harboring Magnolia dealbata, a threatened species and bioculturally relevant tree for the Chinantecan, Mazatecan, Nahuan, and Zapotecan ethnicities in southern Mexico. Particularly, we aimed to: (a) determine factors explaining major community gradients at different heterogeneity scales along a small-scale elevational gradient, (b) test the Decreasing and the Continuum hypotheses along elevation, and (c) classify vegetation to assist in identifying conservation priorities. We used a stratified random sampling scheme for 21 woody stands along a small-scale (352 m) elevational transect. Four main data matrices were used (presence-absence, density, basal area, and guild data). Through Non-metric Multidimensional Scaling (NMS), Principal Coordinates Analysis (PCoA), and distance-based Redundancy Analysis (db-RDA), we found that major community variation was explained by soil pH, displaying an outstanding vegetation discontinuity, separating the species-rich relic Oreomunnea-Ticodendron-stands from stands with higher importance values for M. dealbata. The high species richness observed was explained by a combination of the windward effect of dry-seasonal maximum cloud condensation gain and habitat differentiation-specialization, a phenomenon that may also explain the mid-peak hypothesis and ensure the survival of relic species. Sampling-truncation and conservation status also played a role in this. Our results do not support the Decreasing and Continuum hypotheses along elevation.