The taxonomy of the family Linaceae has not been updated for over two decades and, particularly in Mexico, there is no work evaluating the taxonomic status of all its species. This study provides an update and integrates each of the taxa in the family Linaceae distributed in Mexico. Specimens of plants of this family collected from across the distribution range in Mexico and deposited in herbaria and digital databases, as well as specialized literature, were reviewed. Twenty-four native and one introduced species belonging to two genera, in addition to two varieties, were recognized for the family; the rate of endemism is more than 50% and all native species are under some threat. Reflecting the previously limited knowledge of the group, many of the specimens that we studied had been misidentified. We provide morphological descriptions, supplemented with photographs, illustrations, morphological descriptions, synonymy, ecological data, assessment of conservation status, and a key to differentiate these species. Results presented here reduce the number of native Linum species present in Mexico, modify the distribution range of others, provide data about conservation, as well as new records, and support the presence of the genus Hesperolinon in Mexican territory.

The morphological characteristics of pollen grains of Linum species in Mexico have not previously been evaluated in quantitative terms. This study reports statistical values of pollen characteristics – polar axis, equatorial axis, shape, polar area, exine thickness, sexine thickness, nexine thickness, and height and diameter of ornamental pollen elements – of 11 of the 13 endemic species accepted to date and for which material was available: L. cruciata, L. flagellare, L. lasiocarpum, L. longipes, L. mexicanum, L. modestum, L. orizabae, L. pringlei, L. rzedowskii, L. scabrellum, and L. tenellum. The detailed light and scanning electron microscopy study revealed that the pollen is prolate-spheroidal to subprolate, tricolpate and with semitectate exine sculptured with bacula, clavae, gemmae or spines whose height and diameter follow a homogeneous, intermediate, or heterogeneous pattern. The principal component analysis found that five characters, namely the height of the ornamental elements, sexine thickness, exine thickness, diameter of ornamental elements, and nexine thickness, explained the highest percentage of the variance between species. The cluster and discriminant analyses classified some of the species into three groups and differentiated three of them according to their morphology. The difficulty in distinguishing some species through a conventional approach was solved conveniently using palynological traits since the ornamentation pattern of pollen grains was unique and because grains of various species were statistically different, thus representing a tool for identifying Linum species.