Ovicula biradiata, a new genus of Compositae from Big Bend National Park in Trans-Pecos Texas

Abstract

Here, we describe and illustrate a new monospecific genus of Compositae, Ovicula biradiata gen. et sp. nov., from the Chihuahuan Desert in Big Bend National Park, Texas. Ovicula biradiata is a very locally abundant, yet range-limited, spring annual herb found in coarse calcareous alluvium. Based on its pistillate ray florets, pappus of hyaline, aristate scales, tomentose foliage and slightly saucer-shaped to flat, epaleate receptacle, we determine that the new species has affinities with the Helenioid subtribe Tetraneurinae in the Heliantheae alliance. Molecular phylogenetic analysis of nrDNA (ITS) sequence data supports the phylogenetic position of Ovicula biradiata within the subtribe Tetraneurinae, where it is resolved as the sister lineage to the genus Psilostrophe. We also present detailed habitat information, high-resolution images captured using a dissecting microscope and scanning electron micrographs of vegetative and reproductive characters of Ovicula biradiata and related taxa, as well as provide an updated key to the genera of Tetraneurinae. Finally, we discuss the significance of this remarkable discovery for community science, biodiversity exploration and plant conservation in the Chihuahuan Desert.