Pilosella riloensis Szeląg & Vladimirov, 2025

Szeląg, Zbigniew & Vladimirov, Vladimir, 2025, Pilosella riloensis (Asteraceae), a new hybridogenous species and nomenclatural notes on P. pseudopilosella in Bulgaria, Phytotaxa 704 (2), pp. 203-207 : 204-205

Pilosella riloensis Szeląg & Vladimirov , sp. nov. ( Figs. 1–2)

Type: ― BULGARIA. Rila Mountains , Ribnite ezera glacial valley, grassy places between loose Pinus mugo thickets, ca 150 m west of the hut, 2250 m a.s.l., 13 August 2019, Z. Szeląg (holotype KRAM; isotypes SOM, Herb. Hierac. Z. Szeląg) .

Paratypes: ― BULGARIA. Rila Mountains, along a tourist road from Yastrebets hut to Musala hut, grassy places amongst thickets of Pinus mugo , 2330 m a.s.l., 3 August 2018, V. Vladimirov & Z. Szeląg ( SOM, Herb. Hierac. Z. Szeląg).

Description: ―Phyllopodous. Monocephalous, or with two capitula on erect peduncles up to 15 cm long. Stolons absent. Stem up to 20–25 cm high, in the lower third with dense stellate hairs, and sparse, pale trichomes up to 10 mm long; in middle part with dense stellate hairs, scattered, black in the lower half trichomes up to 5 mm long, and few black glandular hairs 0.2–0.4 mm long; in the upper third with dense stellate hairs, numerous black (with grey apex) simple trichomes up to 8 mm long, and scattered black glandular hairs 0.3–0.5 mm long. Peduncles with dense stellate hairs, numerous, dark grey, simple trichomes up to 8 mm long, and numerous to dense black glandular hairs 0.3–0.5 mm long. Rosette leaves 5–10, up to 12 cm long and up to 1.5 cm wide, lanceolate, entire, subacute at apex (the outer leaves shorter and rounded at apex); on upper surface pale green with numerous pale, simple trichomes 4–5 mm long, and sparse to scattered stellate hairs; on lower surface with protruding pale midrib, and with dense stellate hairs, only on margins and occasionally on midrib with sparse pale, simple trichomes 2–3 mm long. Cauline leaves usually two, up to 4 cm long and up to 0.5 cm wide, lanceolate, sessile, acute at apex, with an indumentum like the rosette leaves. Involucres 10–11 mm long and 10–12 mm wide, globose at base, with very dense indumentum. Involucral bracts acute at apex, up to 1.8 mm wide at base, with dense, dark grey, black-based simple trichomes 5–7 mm long, dense stellate hairs, and scattered dark glandular hairs 0.3 mm long. Ligules yellow, with or without pale red stripes, flat, glabrous at apex. Styles pure yellow. Achenes light brown, 1.8–2.2 mm long. Pappus white. Pollen absent. Flowering: August.

Ploidy level and mode of reproduction: ―2n ~ 3x ~ 27, agamospermous.

Distribution and habitats: ―Endemic to the Rila Mountains, currently known from two localities in the core of the mountains but additional localities are to be expected. In 2019, its population in the type locality comprised more than two hundred flowering plants growing in a few clusters, on grassy places amongst the loose thickets of Pinus mugo , at 2250–2270 m a.s.l. (Fig. 3). In 2018, the second population of Pilosella riloensis along a tourist road from Yastrebets hut to Musala hut seemed to be slightly smaller.

Affinity: ― Pilosella riloensis is triploid whereas its supposed parental species P. kalinensis and P. sericochrota are diploids ( Pavlova 1999; Vladimirov & Szeląg 2001; Szeląg & Vladimirov 2025). The intermediate morphological position of P. riloensis is summarized as follows:

Nomenclatural changes: ― Pilosella pseudopilosella (Tenore) Soják (1971: 217) , originally described as Hieracium pseudopilosella ( Tenore 1811 –1815 [suppl. 2]: 71), is the collective species which comprises 8 subspecies in the Mediterranean area ( Zahn 1923). The nominal taxon occurs in Italy. In Bulgaria, it is represented by H. pseudopilosella subsp. sericochrotum Zahn in Ascherson & Graebner (1922: 60), characterized by long, thin stolons and dense glandular hairs on peduncles. As this name is unavailable in the genus Pilosella Hill (1756: 441) , following the accepted taxonomic concept to recognize Hieracium Linnaeus (1753: 799) and Pilosella as separate genera ( Schultz & Schultz-Bipontinus 1862; Schou 2001; Tyler 2001; Sennikov 2003), we propose a new generic combination, also elevating Hieracium pseudopilosella subsp. sericochrotum to species rank within Pilosella . The name is lectotypified from specimens collected by Johan Wagner in the Rila Mountains and examined by Zahn (1922).