Centranthus pontecorvi Bacchetta & Brullo, 2024

Bacchetta, Gianluigi, Cambria, Salvatore, Castro, Olga De, Fenu, Giuseppe & Brullo, Salvatore, 2024, Centranthus pontecorvi (Valerianaceae) a new species from Sardinia, Phytotaxa 661 (3), pp. 253-266 : 255-258

1. Centranthus pontecorvi Bacchetta & Brullo , sp. nov. ( Figs. 1–2 )

Diagnosis. Centranthus pontecorvi differs from C. trinervis for its simple, all basal stems, leaves ovate to linear-lanceolate up to 3.5 cm wide, axillary twigs absent or rare and subsessile, inflorescence always compact, floral bracts up to 3.5 mm long, ovary 1.5–2 mm long and 0.9–1 mm wide, calyx teeth 16–17, pappus 4–4.5 mm long, corolla white or pinkish-white, 4.5–6 mm long, with tube 2–3 mm long and lobes 1.5–2.7 × 1–1.9 mm, stem filament 1.2 mm long, anther 1.4–1.5 mm long, style 4.8–5 mm long, cypsela ovate-oblong, larger (3–3.5 × 1.5–1.7 mm).

Type. ITALY. Sardinia: Monte Perda, San Benedetto (Iglesias), metadolomie cambriane, 657 m s.l.m., esp. SW, 39°21’54.38”N, 8°31’56.30”E, 14 April 2024, G. Bacchetta, T. Carai & E. Pontecorvo s.n. (holotype CAG!, isotypes CAG!, CAT!, FI!).

Description. Plant in tufts (20–)25–40(–45) cm tall when flowering, with simple basal branches without axillary twigs or few and subsessile. Stems fistulous, robust. Leaves glaucescent-green, ovate to lanceolate, sometimes linear-lanceolate, (2.4–)3–8.5(–10) × (0.7–)1–3.5(–4) cm. Inflorescence in thyrse more or less compact (1.6–)2–4(–4.5) cm long at flowering, (4–)4.5–8(–10) cm long when mature. Bracts ovate-lanceolate 1.5–3.5 mm long. Ovary ovate, 1.5–2 × 0.9–1 mm, dorsally with a central rib, ventrally with 3 ribs and folded at the edges. Calyx with coronula 0.8–1 mm long, provided with 16–17 teeth, hairs of pappus 4–4.5 mm long, plumose with lax feathers 0.3–0.5 mm long. Corolla white to pinkish-white, 4.5–6 mm long, with tube 2–3 mm long, provided with a small lateral hump, and 5 lobes 1.5–2.7 × 1–1.9 mm. Staminal filament 1.2–1.25 mm long, provided with one anther 1.4–1.5 mm long. Style 4.8–5 mm long. Cypsela ovate-oblong, 3–3.5 × 1.5–1.7 mm.

Etymology. The species is dedicated to Cristiano Pontecorvo, botanist of Cagliari University (1971–2023), prematurely disappeared, who during his career has investigated the flora of Sulcitano-Iglesiente biogeographic sector of southern Sardinia, where the new species grows. For the specific epithet, the authors preferred to Latinize the name Pontecorvo into Pontecorvus, which in the genitive is declined into “ pontecorvi ”.

Phenology. Flowering March to April, fruiting May to June.

Ecology and distribution. Centranthus pontecorvi is a glareicolous species growing on Cambrian metadolomites and metalimestones, belonging to the Nebida and Gonnesa geological formations ( Carmignani et al. 2001), at an elevation of 565–715 m a.s.l. This species is a member of a plant community differentiated by some Sardinian and Cyrno-Sardinian endemics, such as Dianthus cyatophorus Moris in Moris & Delponte (1852: 32), Helichrysum microphyllum Cambessèdes (1827: 272) subsp. tyrrhenicum Bacchetta, Brullo & Giusso in Angiolini et al. (2005: 272), and Santolina corsica Jordan & Fourreau (1869: 9). It is narrowly localized in the upper part of Mt. Perda ( Fig. 3 ), near San Benedetto village (municipality of Iglesias, SW Sardinia), where it is represented by few groups of individuals. Based on field observations, this species is limited to a very narrow area of approximately 1 ha, where it grows in the sunny clearings constituted by deposits of incoherent clasts within the meso-mediterranean bioclimatic belt. This species is endemic to the Sulcitano-Iglesiente biogeographical sector, more precisely to the Iglesiente subsector ( Fenu et al. 2014).

Conservation status. The population is threatened by goat and deer grazing. During the monitored period (2018– 2024), a continuous decline in population size was observed. The single population comprised 153 mature individuals in 2018, reduce to 149 in 2019, and only 136 in 2024. Considering the restricted Extent of Occurrence (EOO) and Area of Occupancy (AOO), both equal to 8 km 2, the presence of only one location, the continuous decrease in the number of mature individuals, and the population structure, according to the IUCN protocol ( IUCN 2001, 2024), Centranthus pontecorvoi has to be considered Critically Endangered [CR = B1ab(v)+ B2ab(v)+C2a(II)] at a global level, based on criteria B and C.

As part of the projects funded by the Conservatoire Botanique Nationale de Corse (CBNC) and the EU Life Nature Project Seed Force, the Centro Conservazione Biodiversità (Università degli Studi di Cagliari) has initiated a conservation programme. This programme encompasses in situ studies and long-term ex situ conservation efforts at the Sardinian Germplasm Bank (BG-SAR) for all Centranthus species endemic to Sardinia and Corsica, including Centranthus pontecorvoi .

Specimens examined (paratypes). ITALY. Sardinia: Monte Perda, San Benedetto ( Iglesias ), ambienti glareicoli su substrati carbonatici paleozoici, 605 m s.l.m., 39°21’54.38”N, 8°31’56.30”E, 28 June 2016, G. Bacchetta, G. Fenu & C. Usai s.n. (CAG) ; Monte Perda, San Benedetto — Iglesias (SW Sardegna), 665 m s.l.m., 39°21’58.84”N – 8°31’56.64”E, 24 April 2017, G. Bacchetta & G. Fenu s.n. (CAG!, CAT!) ; Monte Perda (San Benedetto, Iglesias ), 675 s.l.m., 39°21’57.71”N – 8°31’57.96”E, 31 March 2024, G. Bacchetta s.n. (CAG!) .

Figures

FIGURE 1. Diagnostic features of Centranthus pontecorvoi. A. Habit. B. Inflorescence. C. Flowers. D. Flower bud. E. Stamen. F. Cypsela dorsal view. G. Cypsela ventral view. H. Cypsela cross section. I. Cypsela with pappus. J. Pappus. K. Pappus feathers. L. Stigma. Illustration by S. Brullo based on living and herbarium material coming from the type locality (CAT).

FIGURE 2. Phenological features of Centranthus pontecorvoi. A. Mt Perda (locus classicus) natural habitat. B. Habit in natural places. C. Detail of flowering plant. D. Detail of fruiting plant. (Photos: G. Bacchetta).

FIGURE 3. General distribution of the species belonging to the Centranthus sect. Nervosae (A). C. trinervis yellow dot, C. amazonum blu dots, C. pontecorvoi red dot. Local distribution of C. pontecorvoi (B) red area.