Background:

Hybridization leads to individuals with atypical phenotypes, leading to taxonomic confusion when hybridizing populations are studied. Micromorphological characters may enable taxonomists to discriminate between parental and hybrid categories due to their simple genetic inheritance.

Species study:

Three oak taxa distributed in the montane regions of the Mexico were studied: Quercus crassifolia, Q. crassipes and their hybrid Q. × dysophylla.

Hypothesis:

We describe the leaf micromorphological and macromorphological variation of these taxa. Specifically, we searched for a unique combination of micromorphological characters in hybrids. We hypothesize that spatial micromorphological variation will match the spatial pattern revealed by a previous genetic study.

Study sites:

Two allopatric stands for each parental species and seven hybrid zones were studied. Individuals within each stand were identified as belonging to parental or hybrid categories following previous genetic analyses.

Methods:

Stomata and trichome types for each taxa were determined through Scanning Electron Microscopy. Eight micromorphological characters for trichomes and stomata and four foliar macromorphological characters were measured.

Results:

We found the presence of both multirradiate and simple stellate non-glandular trichomes as a diagnostic feature of Q. × dysophylla. Overall populations, Q. × dysophylla showed intermediate phenotypes in 70 % of morphological characters. However, hybrid phenotype exhibited geographical variation. Lastly, spatial hybrid’s phenotype variation did not correlate with the spatial genetic pattern previously identified.

Conclusions:

The micromorphological features of Q. × dysophylla may enable taxonomists to accurately discriminate between this taxon and its parental species. Finally, we suggest that micromorphological expression of both parental species and hybrids may be influenced by environmental gradients and microclimates.

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