The hybridization phenomenon is recognized as an important evolutionary force that influences the diversification and evolution of different vascular plant groups. Hence, it is important to identify hybrid individuals. In Mexico, the dry tropical forest (DTF) is considered as the main center of diversification and endemism of the Bursera genus, containing 85% of the approximately 106 described species worldwide. In the Mexican DTF, a complex of Bursera species was identified, which is formed by two putative parental species Bursera bicolor (Will. ex Schltdl.) Engl. and B. glabrifolia (H.B.K) Engl. Their putative hybrids were analyzed using molecular (cpSSR) and chemical markers (monoterpenes, sesquiterpenes, and triterpenes) in two pure sites (one site for each parental species) and two hybrid zones. We tested whether individuals with atypical morphology between B. bicolor and B. glabrifolia from sympatric sites were the result of genetic flow between these two species. A total of 80 individuals were analyzed with 4 microsatellite diagnostic primers and 37 secondary metabolites (SMs). The genetic and chemical markers were highly coincident according to the statistical analyses performed, and they supported the hybridization hypothesis in this Bursera complex, with both species remaining distinct even in sympatric zones. α-Amyrin (b), β-amyrin (a), and β-amyrin (b) (triterpenes) were the SMs that most contributed to differentiating putative parental species according to SIMPER analysis. The putative hybrids registered the highest genetic diversity values along with the highest number of SMs, out of which 11 were novel and distributed as follows: triterpenes > monoterpenes > sesquiterpenes. Finally, the chemical markers of the three analyzed families give a framework for future studies to explore hybridization events between Bursera species.

Bursera bipinnata (DC.) Engl. (B. bipinnata), commonly known as “copal chino,” is a widely distributed Mexican tree found in transitional zones between pine-oak and deciduous forests. It is valued for its high-quality copal resin, traditionally used in ceremonies and offerings. Additionally, B. bipinnata is recognized for its significant value in traditional medicine, particularly in treating ailments associated with inflammation. In this work, the inhibition of nitric oxide (NO) production of the volatile fraction and resin of B. bipinnata in LPS-stimulated RAW 264.7 macrophage cells were demonstrated. In contrast, the volatile fraction exhibited 37.43 ± 7.13% inhibition at a concentration of 40 µg/mL. Chromatographic analyses of the total resin enabled the chemical characterization of eleven pentacyclic triterpenes belonging to the ursane, oleanane, and lupane series, as well as eight monoterpenes. Notably, the structures of compounds 15, 17, and 29–35 are reported for the first time from the resin of Bursera bipinnata. The anti-inflammatory activity observed for B. bipinnata resin in this study may be attributed to its high content of the triterpenes α-amyrin (15, 29.7%) and 3-epilupeol (17, 38.1%), both known for their anti-inflammatory properties. These findings support the traditional use of this copal resin.

Bursera bipinnata is known as “copal chino, is a small tree that grows in steep areas and is part of the transitional populations of pine and oak forests and lowland deciduous forests. It is the taxon with the widest geographic distribution in México and considered a source of high-grade copal resin used in ceremonies and offerings. Also, B. bipinnata is considered to have great value in traditional medicine to treat ailments related to in-flammation. In this work, the anti-inflammatory effects of the volatile fraction and resin of B. bipinnata in LPS-stimulated RAW 264.7 macrophage cells were demonstrated. The resin extract was the best inhibitor with a 65.83 ± 8.53 % of inhibition of NO production with IC50 = 30 ± 3.3 µg/mL. In contrast, its volatile fraction showed a 37.43± 7.13 % of inhibition at 40 µg/mL. GC/MS and LC analysis of the total resin allowed the chemical characterization of eleven pentacyclic triterpenes with ursane, oleanane, and lupane skeletons, and eight monoterpenes. The structures of compounds (15, 17, 29-35) are reported for the first time from the resin of Bursera bipinnata. The anti-inflammatory activity of the most abundant constituents of the resin of B. bipinnata (α-amyrin (15), 3-epilupeol (17) and α-phellandrene (1) has been previously demonstrated which con-firms the activity showed by the resin as well as the traditional use of this important copal resin. The chemical profile of B. bippinata differs from that of other copal resins (e.g. B. copallifera) in the presence of a greater variety of triterpenes in the resin.

Hybridization is frequent in oaks and may drive various evolutionary and ecological effects on involved plant populations and their associated species. Quercus castanea is a species of Mexican red oak that has served as a valuable model for examining the effects of hybridization events. We used a multimarker approach to characterize the morphological expression patterns and chemical production in parental and hybrid genotypes of the Q. castanea × Q. crassipes complex in a hybrid zone in central Mexico. Leaf macro- and micro-morphological (stomata) characters were measured in 27 trees previously recognized as Q. castanea, Q. crassipes, and hybrids (nine trees/taxon). The expression of foliar shape and the production of secondary metabolites and nutritional chemicals between hybrids and parental species were also evaluated. We found that hybrids exhibit a mosaic of macro- and micro-morphological characters, including the expression of intermediate, parental, and transgressive attributes. Parental species were well differentiated based on foliar shapes, with hybrids overlapping in both species, having a greater affinity with Q. crassipes. Chemical analysis also supports three chemical groups, with hybrids producing new metabolites. This multimarker approach evidences the formation of ecological islands in this hybrid oak complex in which Q. castanea is involved, a fact that has consequences at higher levels of organization in ecology.