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Schenk, John [1], Brokaw, Joshua [2], Devitt, Jessica [3], Brokaw, Destiny [4].

Phylogeny and Floral Character Evolution of Mentzelia Section Bicuspidaria (Loasaceae).

Mentzelia section Bicuspidaria (Loasaceae) is a monophyletic group of desert ephemerals that inhabit the complex, heterogeneous landscapes of the southwestern United States and northwestern Mexico. To investigate species circumscriptions and evolutionary relationships in M. section Bicuspidaria, we employed phylogenetic reconstructions based on DNA sequences from the plastid trnL-trnF, trnS-trnfM, ndhF-rpl32, and rpl32-trnL regions and the nuclear ribosomal ITS and ETS regions. Due to evidence of discordant relationships reconstructed from the plastid and nuclear partitions, we used coalescent-based methods in addition to concatenated data sets to estimate the species tree. Maximum likelihood reconstructions based on the combined plastid and nuclear data, as well as the coalescent-based reconstructions, inferred congruent and fully-resolved species-level phylogenies. A monophyletic M. section Bicuspidaria was composed of two clades. The first clade contained species endemic to the United States and included M. reflexa, M. tricuspis, and M. tridentata. The second clade contained species that were at least partially distributed in Mexico, and included M. hirsutissima and M. involucrata. All species of M. section Bicuspidaria were monophyletic, except for M. hirsutissima, in which the northern clade of M. hirsutissima from California and Baja California was sister to M. involucrata, and both, in turn, were sister to a geographically disjunct southern clade of M. hirsutissima from Baja California Sur and Cedros Island. We propose M. hirsutissima var. nesiotes, which corresponds to the southern clade of M. hirsutissima, be recognized at the specific rank as M. nesiotes, thus rendering all species monophyletic. The recognition of M. nesiotes as distinct from M. hirsutissima is further supported by multivariate analyses of morphological data and differences in climate niches, with M. nesiotes inhabiting the Vizcaíno fog desert west of the Peninsular Ranges and M. hirsutissima inhabiting areas further north with higher precipitation and temperature fluctuations primarily east of the Peninsular Ranges. Despite the unusual floral morphology of M. reflexa, molecular phylogenetic reconstructions placed it sister to M. tridentata. Ancestral character state estimations based on the Mentzelia phylogeny suggest the gain and loss of key floral traits, including the loss of the bicuspidate stamens in M. reflexa, as well as homoplasious floral evolution, such as the evolution of floral bracts with white bases.

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1 - Ohio University, Department Of Environmental And Plant Biology, 22 Richland Ave., 401 Porter Hall, Athens, OH, 45701, United States
2 - Abilene Christian University, Biology Dept, ACU Box 27868, Abilene, TX, 79699, United States
3 - 114 Summit Drive, Story City, IA, 50248, United States
4 - Abilene Christian University, Biology, ACU Box 27868, Abilene, TX, 79699, USA

coalescent model
cryptic species
floral traits
species distribution models
VizcaĆ­no Desert

Presentation Type: Oral Paper
Session: SYSTIV, Systematics IV: Eurosids & Basal Asterids
Location: Virtual/Virtual
Date: Wednesday, July 21st, 2021
Time: 3:30 PM(EDT)
Number: SYSTIV003
Abstract ID:124
Candidate for Awards:None

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