Morphological variation in cones and seeds of two species of pinyon pines distributed in a latitudinal gradient of Mexican highlands

Abstract

The intra- and inter-population variation in cones and seeds of Pinus cembroides and Pinus johannis from central Mexico were analyzed because of the expected effects caused by the wide variation in the latitudinal gradient of the distribution of P. cembroides and P. johannis. The objectives of this study were to identify cone and seed variation in two pinyon species, corroborate taxa-specific identity according to cone and seed characteristics, and detect genetic interactions between species. Cones and seeds from 27 populations distributed in Mexican Altiplano were collected. The cone length, width, peduncle length, cone umbos length, number of scales, seed length and width, and testa thickness were measured. Based on morphological characteristics, population, and species, univariate analysis was performed. Intra-population differences were analyzed using the Kruskal-Wallis test, and interspecific differences were analyzed using the t-test. Discriminant analysis was used to evaluate genetic interactions between species. The cone and seed morphometry between species showed significant differences in cone length, width, umbo length, and seed length. P. johannis showed greater peduncle length and seed testa thickness. Discriminant analysis differentiated the two species and demonstrated eventual hybridization between them. The structures measured in populations of P. cembroides and P. johannis from the center of distribution had intermediate dimensions compared to the northern or southern populations. The cones and seeds of P. cembroides were less variable than those of P. johannis in terms of latitudinal distribution. This information is considered useful for forest management and conservation of specific populations.