Taxonomic identification key with leaf anatomical characters for Pinus L. species in Hidalgo

Abstract

Twelve pine species naturally occur in the state of Hidalgo, of which, Pinus pinceana and P. greggii are listed as threatened. In this context it is necessary to generate information for Pinus species identification specially for immature individuals without seed cones. In this study we establish an identification key based on leaf anatomy for the identification of pine species occurring in the state of Hidalgo. Specimens from different localities were collected from which, permanent slides were prepared from transverse leaf sections and a character matrix was codified from leaf anatomy features and analyzed with UPGMA. The matrix was used to construct an identification key. The key allow for the identification of 10 out of the 12 species, including Pinus greggii a species under risk category. Pinus cembroides can only be differentiated from P. pinceana when it exhibits a semicircular shape in transverse section. External resin canals were only observed in Pinus subgenus Strobus and septal resin canals were only recorded for P. oocarpa. The number of resin canals may only be used as complementary for identification because of its high variation. UPGMA analysis generated two principal clusters, the first group included two interior clusters corresponding with subgenus Strobus species and subgenus Pinus species, the second principal cluster included only species from subgenus Pinus. This study contributes with a robust identification key for pine species at a local scale exclusively using secondary leaf anatomy characters.