First photograph of Ovicula biradiata taken by Deb Manley on 2 March 2024.

Researchers examining individuals in habitat. A Patty Manning scanning the ground in appropriate habitat for individuals of Ovicula biradiata B NPS botanist Carolyn Whiting photographing O. biradiata (circled in red). Photos by Cathy Hoyt on 20 April 2024.

Known habitat of Ovicula biradiata. A, B Habitat with evident pediment slopes C slight habitat variation with iron-bearing rocks present in calcareous cobbles D overview of population locality with individual plants circled in red E close-up of individual plants in habitat illustrating cryptic appearance amongst calcareous surficial deposits. Photos by James Bailey (A) in April 2024 and Deb Manley on 20 April 2024 (B–E).

Images of Ovicula biradiata individuals representing the “small” growth habit that occurs most frequently in all three known locations. Photographs by James Bailey in April 2024 (A), Kelsey Wogan on 27 April 2024 (B, E), Cathy Hoyt on 2 March 2024 (C), Dana Sloan on 27 April 2024 (D).

Examples of moderately sized individuals found occasionally throughout the known locations. Photographs by Cathy Hoyt (A) & Deb Manley (B) on 2 March 2024 and James Bailey in April 2024 (C).

Largest individuals of Ovicula biradiata encountered by researchers in known localities thus far. Photographs by Deb Manley (A, B) on 20 April 2024 & A. Michael Powell (C) on 27 April 2024.

Scan of the Holotype of Ovicula biradiata.

Line drawing of Ovicula biradiata gen. et. sp. nov. A Ray floret without cypsela B disc floret without cypsela C cypsela D habit with close up of leaf surface illustrating nature of indumentum. Illustration by Ellen Ruggia, based on material from the paratype (Manley 3).

Approximate range map of Ovicula biradiata. Geographical location of the known range of O. biradiata in Big Bend National Park in Brewster County, Texas. The boundaries of the park are illustrated in dark green. The purple dot marks the approximate area where three sub populations, each with abundant individuals of O. biradiata, were located. An inset illustrates the location of the study site within the Chihuahuan Desert.

Phylogenetic relationships of Ovicula biradiata and representative photographs of genera of Helenieae. A Maximum Likelihood (ML) phylogenetic tree of Helenieae, based on an aligned matrix of nrDNA sequence data from the Internal Transcribed Spacer region. ITS sequences generated as part of this study have collector numbers indicated to the right. Subtribes are indicated with text. Ovicula biradiata is in bold B Tetraneuris scaposa C Hymenoxys cooperi D Ovicula biradiata E Psilostrophe tagetina F Amblyolepis setigera G Baileya pleniradiata H Gaillardia pulchella I Helenium amphibolum. Photographs by Peri Lee Pipkin (C) and James Bailey (B, D–I).

Scanning electron micrographs (SEM) of Ovicula biradiata. A Cypsela trichomes appear stiff, linear and end in a bifurcate (forked) tip B trichomes on leaf surface with a flexible, helical structure C short-stalked capitate glands on abaxial surface of ray corolla D pollen E ray floret without cypsela F disc corolla apex G anther column and exserted stigma H pappus palea tip with fine pleated serrations I style branch apex, with papillate trichomes sweeping pollen grains.

Scanning electron micrographs (SEM) of various genera of Tetraneurinae. A Pappus of Amblyolepis setigera B pollen of A. setigera C short-stalked capitate glands on disc corolla of Baileya pauciradiata D stiff, twin hairs on cypsela of Hymenoxys cooperi E hyaline, aristate palea-like pappus of Hymenoxys cooperi F vesicular trichomes on abaxial surface of disc corolla lobes in Psilostrophe bakeri G ridges on the surface of a cypsela in P. bakeri H sweeping papillate trichomes on style branch apices in Tetraneuris scaposa I paleaceous pappus of T. scaposa with terminal, antrorsely setose bristle.