Sideritis royoi (Lamiaceae), A New Orophilous Species from Northeastern Spain

1. Introduction

Sideritis L. is a large genus of family Lamiaceae Martynov, nom. cons., that includes nearly 150 species, mainly distributed in Europe, North Africa, Macaronesia and Western and Central Asia [1,2,3], though some of which are introduced or naturalised in other areas. The Port Massif (northeastern Spain, Tarragona Province), exhibits high plant species richness and endemism [4]. During field work and posterior study of herbarium materials from this mountainous area, some specimens of Sideritis L. caught our attention due to a combination of characteristics that do not match those of any described species within the genus. The presence in the upper areas of the Port Massif of plants of the genus Sideritis, whose identity is uncertain, dates back more than 40 years. These plants had initially been collected by the local botanist Lluís de Torres in 1982 at the base of Caro (the highest mountain in the area), but strikingly it was not listed in the floristic catalogue of the Port Massif [5]. Subsequently, Buira et al. [6], including two of the authors of this paper (LS and RC), tentatively attributed those plants to S. hyssopifolia L., but remarking some discordant morphological characters. The most recent reference to the Sideritis occurring in the upper parts of the Port Massif is due to Sáez and Aymerich [7], who (in comments on S. hyssopifolia) indicated that the taxonomic identity of those populations was unclear.

In order to clarify that point, during field trips between 2021 and 2023 we gathered new specimens of the Sideritis from the Port Massif, which had doubtfully been attributed to S. hyssopifolia. The study of the material collected, herbarium specimens, literature, photographs and field observations, revealed that the Port Massif plants do not fit with any currently accepted species within the genus and represent a new species, herein described.

2. Materials and Methods

The present morphological and comparative study is based on examination of herbarium specimens. In addition, field observations were made on individuals from the populations of the Port Massif area. Morphological characters, recognised as taxonomically discriminant within Sideritis, were studied according to Obón and Rivera [1], Rivera et al. [8,9], and Ríos et al. [10]. Morphological observations of materials were carried out under a binocular stereoscopic microscope Zeiss Stemi DV4. We examined material of morphologically related species held mostly at the herbaria ABH, BC, and MUB. Authors of the taxa cited in the text follow IPNI [11], and the herbarium acronyms accord with Thiers [12]. Representative herbarium material examined is listed in the Appendix. Bioclimatic classification conforms to Rivas-Martínez [13], and biogeographical data follow Rivas-Martínez [14]. To evaluate the conservation status of the new species, the IUCN Red List Categories and Criteria [15,16] were used.

3. Results

The combination of morphological characters with diagnostic value, the biogeographical data, and a review of the foremost regional floras and taxonomic revisions [1,10,17] suggested that the plants collected in the Port Massif area are distinct enough to merit recognition as a new taxon, for which we believe the rank of species to be the most appropriate, and which we describe herein.

3.1. Taxonomic Treatment

Sideritis royoi L.Sáez, R.Curto & M.B.Crespo, sp. nov. Figure 1 and Figure 2.

Holotype: SPAIN. Catalonia, Tarragona province: Baix Ebre, Roquetes, La Barcina, 31TBF7723, limestone rocks, 1250 m a.s.l., 16 July 2023, R. Curto s.n. (ABH 83741!). Isotype: BC 849997!

Diagnosis: Sideritis royoi differs from S. hyssopifolia by the lower leaves (main surface) glabrous or rarely glabrescent (vs. hairy); the upper leaves subspinescent and narrower than the lower (vs. non-subspinescent and similar to the lower); the adaxial and abaxial surfaces of the bracts lacking eglandular hairs (vs. eglandular hairs present); and the shorter inflorescence, with 1–2(–3) verticillasters (vs. longer inflorescence, with (1–)2–13 verticillasters).

Description: Dwarf shrub. Woody basal parts 7–14 cm including branches, decumbent to suberect. Non-woody branches 8–30 cm long, ascending to erect. Branchlets with goniotrichous and homotrichous trichomes, with scarce to abundant glandular hairs up to 0.1 mm long and lacking glands; trichomes scarce, antrorse, 0.2–1 mm long, with 2–3(4) cells cylindrical, the apical one conical. Leaves greenish subspatulate to sublinear, with main surfaces glabrous or glabrescent, with very scarce eglandular hairs 0.2–0.7 mm long, patent mainly at the margins and at the midrib of the adaxial surface, with scarce glandular hairs up to 0.1 mm long and always lacking sessile glands; lower and middle leaves 8–32 × 3–12 mm, 2–4-dentate, apiculate or mucronate at the apex; upper leaves 6–15 × 2–4 mm, subspinescent, usually 2-dentate, sometimes entire; axillary fascicles of leaves usually absent at the flowering time. Inflorescence commonly yellowish or greenish, ovoid to globose, 0.7–2.5 cm (rarely up to 4 cm) long, with 1–2(–3) verticillasters, the central 3–3.5 mm apart; axis usually yellowish or greenish, with sparse sessile glands and glandular hairs up to 0.1 mm long abundant antrorse eglandular hairs 0.2–0.8 mm long. Bracts greenish to yellowish, erect, ovate, with the widest part towards its basal third; divided to 1/3–1/2 of its width; adaxial surface glabrous, abaxial with sparse (sometimes abundant) glandular hairs up to 0.1 mm long and always lacking sessile glands; eglandular hairs usually absent, sometimes present (very scarce) at the margins, 0.2–0.5 mm long; lower bracts 7–9 × 6–10 mm, with 3–8 teeth on each side; middle bracts 8–10 × 9–12 mm, divided to 1/3–1/2 of its width, with 6–10 teeth on each side. Verticillasters 6-flowered. Calyx campanulate, 8–11 mm long, with five subequal divergent teeth, 4–8 mm long, ending in spines 0.7–2 mm long; the outer surface with scarce to abundant glandular hairs up to 0.15 mm long, sessile glands and antrorse eglandular hairs 0.5–1.8 mm long; carpostegium discontinuous to more or less continuous. Corolla yellowish, 6–9 mm long; upper lip bifid up to 1/5–1/3 of its length; stamens included in the corolla tube, with short filaments 0.3–0.5 mm long; style 1.8–2.5 mm long. Nutlets ovoid, c. 2 × 1.5 mm.

Eponymy: The new species is dedicated to the late Ferran Royo Pla (1969–2016), for his outstanding work to improve the botanical knowledge of the Port Massif.

Phenology: Flowering is from June to early July; fruiting is from late July to late August.

Distribution and ecology: Sideritis royoi is an orophilous species endemic to a small area in the Port Massif. The new species is found in the rocky slopes and in patches in the understory of the open Pinus sylvestris L. forests at the northern face of Caro-La Barcina mountain, between 1080 and 1325 m a.s.l. The known sites of the new species show a pluviseasonal Mediterranean bioclimate, mostly within the Supramediterranean thermotype and with a Subhumid or locally Lower Humid ombrotype [13]. Biogeographically, this area belongs to the Puertobeceitan-Morellan District of the Western-Catalanid subsector (Valencian-Tarraconensian Sector, Catalan-Provencian-Balear Province, Mediterranean Region), according to Rivas-Martínez [14]. The Caro-La Barcina mountain hosts a rich flora including a high number of endemic plant species to northeastern Iberian Peninsula [4], some of them restricted to the Port Massif. Font Quer [18] first noticed that several plant species occurring in the Port Massif usually showed conspicuous morphological differences compared with other related taxa occurring in other areas of northeastern Iberian Peninsula. The new species grows together with several Puertobeceitan-Morellan endemics, such as Aquilegia paui Font Quer, Arenaria conimbricensis subsp. viridis (Font Quer) Font Quer, Knautia rupicola (Willk.) Font Quer, or Thymus willkommii Ronniger, as well as more widely distributed orophilous species such Arctostaphylos uva-ursi (L.) Spreng., Erinacea anthyllis Link subsp. anthyllis, Festuca trichophylla (Gaudin) K.Richt. and Teucrium aureum Schreb. subsp. aureum.

Conservation status: Based on the present state of knowledge, the extent of occurrence (EOO) and area of occupancy (AOO) of Sideritis royoi seem quite restricted (less than 5 km²), which suggest categorising it as “Vulnerable” (VU), mainly according to IUCN criterion D2 [15]. However, further field studies are needed to define a more accurate conservation category of this species.

Additional specimens examined: SPAIN. Tarragona Province: Alfara de Carles, prop de les Clotes, 1080 m a.s.l., 10 July 1982, L.Torres (MMA); per davall del Pas de la Barcina, cara Nord, 1200 m a.s.l., 14 July 2009, Aparicio, Beltran, Curto, Mesa & Royo 6085 (MMA); La Barcina, matollar, 31TBF72, 1270 m a.s.l., 25 July 2021, R.Curto (L. Sáez herb. pers.).

4. Discussion

Sideritis royoi shows morphological affinities with taxa of S. sect. Sideritis subsect. Hyssopifoliae Obón & D.Rivera and is assumed to belong here, based on its hair covering at the base of branchlets goniotrichous (or slightly holotrichous) with antrorse trichomes [1]. Most of the taxa belonging to this group are found in mountain areas of the Iberian Peninsula and Northern Africa, with a higher concentration in Southern and Eastern Spain. Some of these species are orophyte specialists that are narrowly endemic to a reduced mountain range [1,10]. A comparison of S. royoi with morphologically related species belonging to S. subsect. Hyssopifoliae is shown in Table 1.

The type species of this subsection, S. hyssopifolia, is quite variable, particularly in habit, and size of stems, leaves and flowers. Several variants are treated at species or infraspecific ranks [1,17,19], or even included in synonymy [17]. This is the case of S. brachycalyx Pau (≡ S. hyssopifolia var. brachycalyx (Pau) Font Quer), an entity often regarded as a distinct species based mostly on the lack of carpostegium. However, this is also a variable character, even inconstant in S. brachycalyx. Therefore, for practical purposes S. hyssopifolia is considered in this work in a broad sense to include S. brachycalyx, a taxon that in our opinion is best to treat as subspecies or variety in the former [20].

Sideritis hyssopifolia is apparently closely related to S. royoi, with which it shares the goniotrichous and homotrichous hair covering at base of branchlets, the general habit and calyx shape, size and indumentum. However, S. royoi differs from S. hyssopifolia in several striking characters (see Table 1). Most importantly, the leaves glabrous on main surfaces, the subspinescent upper leaves, the absence of eglandular hairs ont the main surfaces of the bracts (Figure 1A) and shorter inflorescences, while S. hyssopifolia has usually hairy leaves, non subspinescent upper leaves, eglandular hairs on the main surfaces of the bracts and longer inflorescences.

Weaker similarities were also observed with other taxa in S. subsection Hyssopifoliae. Sideritis pungens (including subsp. vigoi Peris et al., and also for practicity S. javalambrensis Pau ≡ S. pungens subsp. javalambrensis (Pau) Obón & D.Rivera) differ from the new species mainly by heterotrichous hair covering at base of branchlets, entire lower leaves, cylindrical inflorescences, adaxial surface of middle bracts hairy, and shorter calyces with carpostegium continuous. Differences between S. pungens and S. javalambrensis to other related orophilous taxa were highlighted by López-Udias [21].

Sideritis carbonellii Socorro and S. tugiensis S.Ríos et al., two species closely related to each other that occur in southern Spain, are much more different morphologically. They are easily separated from S. royoi by the base of branchlets with holotrichous hairs and glands, main surface of leaves hairy, longer inflorescence, fewer teeth on middle bracts and shorter calyces. See Ríos et al. [10], López-Udias [21], and table 1 for the differences between S. carbonellii and S. tugiensis.

Finally, morphological relationships with species belonging to S. subsect. Fruticulosae Obón & D.Rivera seem to be remote. It was suggested that the plants now described as S. royoi might be the result of introgression with S. spinulosa Barnades ex Asso [6], because of the presence of subespinescent upper leaves in S. royoi. Our results indicate that the morphological differences between S. spinulosa and S. royoi are notable, allowing for a clear separation between those two species. Sideritis spinulosa differs by holotrichous hair covering at base of branchlets, leaves with scarce glands and abundant trichomes 1.5–2.0 mm long, cylindrical inflorescences with 3–15 verticillasters, the abaxial surface of middle bracts with scarce glands and scarce to abundant trichomes (0.5–1.5 mm long) and calyx with carpostegium continuous. Another species of S. subsect. Fruticulosae occurring in the Port Massif, but in lower areas (up to 750 m a.s.l. altitude) is S. fruticulosa Pourr. This species differs from S. royoi by holotrichous hair covering at base of branchlets, leaves with scarce glands and abundant trichomes 0.3–1.5 mm long, cylindrical inflorescences with 3–7 verticillasters, the abaxial surface of middle bracts with scarce glands and scarce to abundant trichomes (1.0 mm long) and calyx with carpostegium continuous. In a recent and detailed taxonomic revision of S. fruticulosa [22], four subspecies are recognized, none of them approaching to the morphological characteristics of S. royoi. Interestingly, Roselló et al. [22], who were very sensitive to detecting small morphological variations and hybrids, indicate no morphological relationship or existence of hybrids with S. hyssopifolia. Further, we have not observed S. spinulosa or S. fruticulosa in the locations where S. royoi occurs. Finally, regarding the suggested possible hybrid origin, S. hyssopifolia is widespread in Northern Iberian Peninsula, mainly in the Pyrenees [10,23], but the species is not known from the Port Massif [5,23] and thus no range overlap with S. royoi occurs. Further molecular and cytogenetic work will help to elucidate this point.