Euphorbia guadalhorcensis Casim.-Sor. Solanas & Hidalgo-Triana

Solanas, Federico Casimiro-Soriguer & Hidalgo-Triana, Noelia, 2023, A new taxon of Euphorbia (Euphorbiaceae) from the southern Iberian Peninsula (Andalusia, Spain), Phytotaxa 579 (1), pp. 1-16 : 3-4

Euphorbia guadalhorcensis Casim.-Sor. Solanas & Hidalgo-Triana , sp. nov. ( Figs. 1–2 ).

Type:— SPAIN. Málaga province : Pizarra , Hacho de Pizarra, Castillejos de Luna, roquedos, molasas, 30SUF4869, 190– 200 m, 2 June 2021, F. Soriguer s.n. (holotypus MGC 94769!, isotypi MA!, MGC 94770!, GDA!) .

Diagnosis: — Euphorbia guadalhorcensis differs from the other taxa of sect. Paralias (sensu Riina et al. 2013) in the following combination of morphological characteristics: chamaephytic and erect habit, and presence of indumentum of short hairs on the leaves, stems, dichasia, cyathia, and fruits, and in the greater length of the caruncle ( Table 2 ).

Description:— Perennial plant, small shrub up to 50 cm tall, with short and erect, unicellular hairs, up to 0.1 mm. Woody stems except at the top, erect, the upper ones very branched, pubescent. Cauline leaves (5–)6.5–20(–26) × (1.3–)1.5–3.5(–3.9) mm, laxly disposed, pubescent, narrowly oblanceolate, apex acute, apiculate, base attenuate, margin entire, sessile, and deciduous. Pleiochasium with 2–5 primary rays, 1–6 cm long, pubescent; ray-leaves 4–11 × 2.5–4 mm, elliptic to rhomboid or like cauline leaves, apex apiculate, deciduous, pubescent. Dichasium simple or divided 1–2 times, pubescent; raylet leaves 2.5–6.5 × 3–11 mm, free, reniform or semi-circular, apiculate, pubescent. Cyathium 0.9–1.8 mm long, campanulate, very pubescent; cyathial glands 4, yellow to orange, with 2 horn-like appendages, (0.1–) 0.2–0.5 mm, triangular, rarely setaceous. Ovary hairy; styles 3, hairy; bifid stigma. Capsule 2.5–3.6 × 2.4–3.8 mm, sulcate, trilobate, subglobose, with a pedicel (0.8–)1–2(–2.5) mm long, pubescent; cocci rounded, laxly hairy at the base and keels, rugose-granulate at keels. Seeds (1.5–)1.7–2(–2.2) × 1.2–1.6 mm, carunculate, ovoid, testa reticulate-foveolate, brown or greyish; caruncle 0.7–1 × 0.6–1.1 mm, conical; length of caruncle/length of seed (excluding caruncle) = (0.33–)0.4–0.48(–0.51).

Phenology:— Flowering from February to May and fruiting from May to August.

Distribution and habitat:— Euphorbia guadalhorcensis is endemic to the southern edge of the Iberian Peninsula ( Fig. 3 ). Its distribution is restricted to the rocky, low mountains of Sierra del Hacho de Pizarra and Sierra del Hacho de Álora, both localized in the Guadalhorce River Valley (Málaga province, Spain). This valley constitutes the entire Malacitano subsector (Malacitano-Axarquiense Sector, Betic Province, Mediterranean Region; cf. Pérez-Latorre et al. 2008, 2019). The new species grows in cliffs, screes, and other rocky places, always on sandy and stony soils derivate from molasses (a mixture of calcareous sandstones with conglomerates), forming part of rupicolous communities and xerophilous open scrublands between 200–550 m elevation in the lower thermomediterranean thermotype with dry ombrotype ( Pérez Latorre et al. 2008) ( Fig. 4 ). All the narrow endemisms of the Malacitano subsector grow in molasse (Valdés 2012, Pérez Latorre et al. 2014, Blanca et al. 2017), like E. guadalhorcensis . These rocky low mountains composed of molasses are also considered as a floristic refuge, as a former maritime island area during the lower Pliocene ( Serrano & Guerra 2004), with some characteristic semiarid relict taxa ( Pérez Latorre et al. 2014). The geographic isolation during the Pliocene and the special ecological characteristics of the area may have been crucial for the divergence of the new species from close relatives in sect. Paralias .

Etymology:— The specific epithet refers to the Guadalhorce River, the most important of the Málaga province. The low part of this river forms one great valley where the low mountains of Sierra del Hacho de Pizarra and Sierra del Hacho de Álora are located, like some kind of rocky islets.

Conservation status:— None of the known populations are in any protected territory under any type of protection. It is a species that presents reduced area of occupancy (7,8 km 2), a reduced extension of the presence (17,63 Km 2), and the presence of only two populations until now (one in the Hacho de Alora and the other one in the Hacho de Pizarra). However, both populations are constituted by a large number of individuals. We suggest that the conservation status of Euphorbia guadalhorcensis should be designated as NT (IUCN 2012), due to the reduced occupancy area (lower than 10 km 2) and because future changes in land use could lead to a significant loss of its habitat.

Figures

FIGURE 1. Euphorbia guadalhorcensis (A. habit; B. upper stems with leaves; C. dichasia). Photos by the authors.

FIGURE 2. Details of morphology of Euphorbia guadalhorcensis (A. apex of leaf; B. abaxial side of leaf; C. medium stem; D. capsule). Photos by the authors.

FIGURE 3. Distribution of Euphorbia guadalhorcensis in the Iberian Peninsula.

FIGURE 4. Habitat of Euphorbia guadalhorcensis (A. xeric rocky slopes and cliffs on the west face of Sierra del Hacho de Pizarra; B. rupicolous vegetation with E. guadalhorcensis growing in molasses in Castillejos de Luna, type locality). Photos by the authors.