Urospermum × siljakii Hidalgo, Balant & Pellicer nothosp. nov.

Type:— SPAIN. Catalonia. Barcelona: Montjuïc, Carrer Doctor Font i Quer, 14 May 2021, O. Hidalgo 682 & M. Balant (holotype BC).

Parentage:— Urospermum dalechampii (Linnaeus 1753: 790) Scopoli ex Schmidt (1795: 276) × Urospermum picroides (Linnaeus 1753: 790) Scopoli ex Schmidt (1795: 275).

Diagnosis:—Plants of Urospermum × siljakii are intermediate between U. dalechampii and U. picroides in most traits. They differ from parental species by the consistency of indumentum, that is not as softly hairy as in U. dalechampii nor as strongly hispid and spinulose as in U. picroides, a trait particularly noticeable on the involucrum bracts.

Description:—Annual to perennial herb. Stem sometimes prostrate in its lowest part, vegetative and sparingly branched, then upright. Leaves entire to pinnatifid, with hispid and spinulose trichomes at least on the veins beneath. Flowering shoot with usually 0–3 branches restricted to the first order as in U. dalechampii, whereas in U. picroides it may present more branches (up to> 20) and of higher order. Capitula 20–45 mm wide (40–70 mm in U. dalechampii, 10–30 mm in U. picroides), on long peduncles. Involucre of generally eight bracts of equal length arranged in a row and connate in their lower third, covered by a slight indumentum of hispid and spinulose trichomes. Floret number per capitulum closer to U. picroides (<150) than to U. dalechampii (> 150). Ligules yellow, sometimes with a dark mark at the apex of petals and a purplish stripe on the outer face. Seeds not developed, suggesting that the hybrid is likely sterile. Chromosome number 2n = 12, intermediate between that of U. dalechampii (2n = 14) and U. picroides (2n = 10). Genome size (i.e., nuclear DNA content) of 2C = 1.89 pg ± 0.01, corresponding to the average value between the genome size of U. dalechampii (2C = 2.26 pg. ± 0.01) and U. picroides (2C = 1.51 pg ± 0.01).

Flowering time:—The phenology of Urospermum × siljakii is similar to its parent species U. dalechampii and U. picroides, all of them flowering mostly in spring from April to June.

Eponymy:— Urospermum × siljakii is named after Prof. Sonja Siljak-Yakovlev (Vršac, Serbia, 8 September 1946 –), Directeur de Recherche Emérite at the Université Paris-Saclay, France, a botanist with a longstanding interest in the Asteraceae. She has been mentor to many researchers working on karyology and cytogenetics, sparing no time and effort to train and connect researchers from all over the world.