The southernmost tip of Texas is a part of the Tamaulipan Province of northeastern Mexico which some authors consider in the Madrean Subkingdom of the Holarctic Kingdom, while others the “Xerofitica Mexicana” of the Neotropical Kingdom. To shed more light on this question, a natural flora of fourteen counties in the S TX Plains ecoregion, South Texas Plains flora (S TX), was compiled, studied from a biogeographical perspective, and analyzed in this work. The analysis was based primarily on the species and genera distribution outlines. Phylogenetic literature was searched to find relationships, patterns of migrations, and geographical connections of the species of major clades. Taxonometric and geographic spectra of the S TX flora were obtained and compared with those of two other floras in southern Texas: SC Texas (EP, or Edwards Plateau) and Big Bend Region (BB). There are 1250 native species in 553 genera and 117 families in the S TX flora. These species were classified into 25 geographic (floristic) elements. Herein is presented a checklist of S TX accompanied by the geoelement descriptions, a comparison of geographical spectra of the species and genera in all three floras, and the biogeographical analysis of the S TX flora. South TX, having a flat topography and being on the crossroads of migration routes, has multiple connections with adjacent floristic centers. The Tamaulipan endemism is not particularly high (8% in S TX) in comparison with much higher Chihuahuan endemism in BB (23% in BB; 10% in S TX). Proportions of taxa of the largest families in the three southern Texas floras show much higher numbers of tropical-subtropical, Tamaulipan, Gulf Coast, and Mesoamerican (coastal) species in the S TX flora in comparison with those of EP and BB. North temperate, E North American, and Prairie species are best represented in EP (47%), followed by S TX (36%), with only 17% in BB. The majority of the BB differential species are in the Chihuahuan, SW N American, Sonoran/Apachian, and the Madrean geoelements. The genera of the largest family, Asteraceae, that are differential among the three floras show importance of the Mexican (Madrean) centers of diversity as well as migrations from the Tethyan Subkingdom in the assembly of the S TX flora. Tethyan connections are also evident among the Boraginaceae s. str. and some other groups found in the flora. The spectra of generic and specific geographical elements of S TX illustrate transitional position of its flora. It represents an ecotone between the Western (Madrean) and the Eastern (Atlantic and Gulf Coast) N American Regions, with a very high influence of the various Neotropical elements and a higher affinity to the EP flora than to that of BB.
Areas of endemism (AEs) are fundamental entities of analysis in biogeography and a key step for biogeographical regionalization. Even though many studies have contributed to the biogeographical knowledge of southern USA flora, no endemicity analysis (EA) has been conducted that would include a large number of native seed plant species from different families. A new analysis of plant spatial patterns is important as a first step for a future updated floristic regionalization of North America North of Mexico. It has become easier to accomplish owing to the increased availability of large-scale digitized distributional data and statistical methods of biogeographic analysis. Here we identify the AEs in SC/SW USA using digitized plant specimen data available from IDigBio. We built a database with 81,851-specimen point records of 400 selected mostly angiosperm species and applied the NDM/VNDM method of endemicity analysis. We then compare the established 26 AEs in the area of study with the floristic provinces in two comparatively recent regionalization systems of USA. To understand the spatial patterns, we also pay attention to the information on relationships of the endemic species found in phylogenetic literature.
The history and connections of the flora of south-central/southwestern (SC/SW) North America have been studied and summarized in biogeographic regionalization. However, some studies show contrasting delineations of the SC/SW North American provinces that could be better determined using quantitative methods. We aimed to find spatial patterns of a set of plants in the SC/SW United States by conducting endemicity analysis (EA) on different scales. We first built a dataset with 81,965 specimen point records of 400 species from 174 genera and 61 families of angiosperms and two genera of gymnosperms using digitized specimen data from iDigBio. We then performed EA at four different scales to identify the areas of endemism (AoEs). We obtained 28 AoEs with different cell sizes by selecting each AoE under the grid size that yielded the highest number of high-scoring species. The study region split into two significant centers of accumulation of nested or partially overlapping AoEs: the SW and SC consensus areas. In these parts of the Nearctic region, many genera/clades, among those in the dataset, showed a geographic split into western and eastern clades. The split corresponded to an environmental and physical barrier known as Cochise Filter Barrier. The Sonora–Mojave arid center, parts of South Texas, and the Chihuahuan Desert harbor basally branching taxa of several genera and even families, based on the observations of some species, which allowed identification of the AoEs.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.