Evolution of Tidestromia (Amaranthaceae) in the deserts of the southwestern United States and Mexico

Abstract

Tidestromia (Gomphrenoideae, Amaranthaceae) is a monophyletic genus restricted to deserts of North America with the highest levels of endemism centered in the Chihuahuan desert. Tidestromia is morphologically distinct from related genera which caused researchers difficulty in identifying its phylogenetic affinities. Recent molecular phylogenetic evidence suggests that a monophyletic Tidestromia is related to Alternanthera and Pedersenia in a well-supported linage referred to as the Alternantheroid clade. Preliminary species circumscription of Tidestromia suggested six species, two subspecies and two varieties. However, this study revealed problems in the current infraspecific classification based on morphology. The current study aims at testing the phylogenetic relationships within the genus using nuclear (ITS), chloroplast (rpl16, trnL-F), and morphological data and examine the role that soils, climate, and habitat have had on speciation in the genus. Earlier researchers hypothesized these environmental features were reproductive barriers driving speciation; however, incongruency between the chloroplast and nuclear datasets with additional support from previous cytogenetic data suggests that hybrid speciation has played a larger role. The total evidence results in a fully resolved ingroup and suggests that all infraspecific taxa are distinct species requiring nomenclatural taxonomic changes. Contrary to previous findings, the annual habit has evolved twice in the genus.

High phylogeographic and genetic diversity of Tidestromia lanuginosa supports full‐glacial refugia for arid‐adapted plants in southern and central Coahuila, Mexico

“…An important factor that might also contribute to the high genetic differentiation found in Tidestromia lanuginosa is its potential adaptation to different environments, including different climatic and edaphic conditions such as gypsum, saline, calcareous, limestone, sandy, granite, and clay soils (Sánchez‐del Pino and Motley, 2010). As currently circumscribed, Tidestromia lanuginosa has an unusually broad ecogeographic distribution, with populations across northern Mexico, ranging from relatively wetter environments on the Gulf of Mexico coast to very dry environments in the center of the Chihuahuan Desert.…”

“…Leaves of 10–20 individuals per population were collected in silica gel (Appendix S1), but we included only up to five individuals per population because González (2015) showed that such sampling was sufficient to represent population variation. Four closely related taxa ( T. gemmata I.M.Johnst., T. rhizomatosa I.M.Johnst., T. tenella I.M.Johnst., and Alternanthera flavescens Kunth) were selected as outgroups based on recent phylogenetic studies (e.g., Sánchez‐del Pino et al, 2009; Sánchez‐del Pino and Motley, 2010). Collecting and voucher information is provided in Appendix 1.…”

“…Total DNA was extracted using the Qiagen Plant DNeasy kit (Qiagen, Valencia, CA, USA) and the manufacturer’s protocol. The plastid trnL‐F intron and spacer region and the psbJ‐petA spacer region were sequenced based on previous studies that demonstrated their informativeness in addressing phylogenetic relationships, including in Tidestromia (Shaw et al, 2007; Sánchez‐del Pino and Motley, 2010; Aguirre‐Liguori et al, 2014). The trnL‐F region was amplified and sequenced using primers “c” and “f” of Taberlet et al (1991), whereas the psbJ‐petA spacer region was amplified using primers “ psbJ” and “ petA” from Shaw et al (2007).…”

“…Tidestromia Standl. comprises a clade of eight herbaceous to suffruticose, C 4 photosynthetic species distributed in the arid regions of northern Mexico and the southwestern United States, with a center of diversity in the Chihuahuan Desert, and especially in Coahuila, where a majority of the species can be found (Henrickson, 1993; Sánchez‐del Pino and Motley, 2010; Bena et al, 2017). Tidestromia lanuginosa is the most widely distributed species in the genus, occurring in arid and semiarid habitats throughout northern Mexico and the southwestern United States, with disjunct populations in the Dominican Republic (Robertson, 1981; Sánchez‐del Pino and Flores‐Olvera, 2006).…”

Molecular phylogenetics of Alternanthera (Gomphrenoideae, Amaranthaceae): resolving a complex taxonomic history caused by different interpretations of morphological characters in a lineage with C4 and C3-C4 intermediate species

“…Similar incongruent results have been demonstrated in the closely related genus Tidestromia . Chromosome evidence related to number and the form of meiotic division indicated hybridization in some members of Tidestromia (Sánchez‐del Pino & Motley, 2010). It is interesting to note that Turner (1994) stated that although two‐thirds of the genera of the Amaranthaceae remain to be counted, polyploidy appears to be common in the family.…”