Introduction

Dionysia Fenzl, one of the larger genera of Primulaceae, consists of more than 50 species. They are suffrutescent herbs that form loose tufts or dense cushions in crevices of rocks and cliffs. During spring, these plants are covered by yellow, purple or pink flowers (Lidén 2007; Grey-Wilson 1989; Melchior 1943; Wendelbo 1961, 1964, 1965, 1971).

The majority of Dionysia species (more than 20) are found in the Zagros Mountains of W Iran (Lidén 2007). The number of species of Dionysia in other regions of SW Asia is lower: there are eight species in other areas of Iran, 11 species in Afghanistan, three in Turkey, two in Iraq, two in Turkmenistan, two in Tajikistan, one in Oman and one in Pakistan. The majority of species of Dionysia occurs in the area covered by Flora iranica (Wendelbo 1965). Thanks to the extensive collection of material from different mountainous areas of this region in recent years, new species have been described (Jamzad 1996, 1999; Lidén 2007; Borjian & al. 2014).

Ilam province in W Iran is a poorly studied area, from which several new species have recently been described (Mozaffarian 2008). Two nearby localities of an unknown Dionysia species were found in the Dinar-Kouh mountains in the Abdanan region of this province by the first author. Here, we report the finding of a new species and clarify its relationships to other species of Dionysia.

Material and methods

Morphology

We compared our unknown species with other Dionysia species reported from W Iran and N Iraq, namely D. bornmuelleri (Pax) Clay, D. gaubae Bornm., D. odora Fenzl and D. tacamahaca Lidén (Wendelbo 1965; Jamzad 1999; Lidén 2007), as well as all Iranian species with similar morphology. All type specimens of the above-mentioned species were studied. Vegetative and floral parts were observed and measured under a stereomicroscope (NTB-3A, Wuzhou New Found Instrument Co., Guangxi, China). Voucher specimens were prepared and deposited in the herbarium of Science and Research Branch, Islamic Azad University (IAUH), Tehran, with duplicates in B and UPS (herbarium codes according to Thiers [continuously updated]).

Fig. 1.

Phylogram obtained from a maximum likelihood (ML) analysis of ITS DNA sequences. The numbers above the branches are ML bootstrap values, the numbers below the branches are posterior probabilities (PP). Bootstrap values equal to or less than 50 % and PP equal to or less than 0.5 are not shown.

Results and Discussion

Material of the new putative species showed some morphological dissimilarity to those species already described from W Iran, as summarized in Table 1. Morphologically, our material also showed resemblance to Dionysia iranica Jamzad and D. sarvestanica Jamzad & Grey-Wilson, which were described from localities further south. Genetically, the new material can be distinguished from these and other species, as shown in Table 2.

We found that the ITS DNA sequence of the new species is most similar to that of Dionysia gaubae and differs from it by only four bases (Table 2 and Fig. 1). MP analysis identified a set of 142 parsimony-informative characters and resulted in 449 most parsimonious trees with a length of 491 steps, a consistency index (CI) of 0.607 and a retention index (RI) of 0.749. The strict consensus tree displayed the following characteristics: length = 502 steps, CI = 0.594, and RI = 0.735 (tree not shown). In all three analyses of the ITS dataset (Fig. 1), our new putative species showed to be closely related to D. gaubae. It did not display close relationships to the morphologically similar species D. iranica and D. sarvestanica. Hence, we conclude that that our newly gathered material indeed represents a new species.

Dionysia robusta Younesi, sp. nov. — Fig. 2 & 3. Holotype: Iran, Ilam Province, SW of Abdanan, Dinar-Kouh protected region, Pizeleh, 32°56′09.6″N, 47°18′35.4″E, 1720 m, 11 May 2015, Younesi 14494 (IAUH; isotypes: B, TARI).

Description — Cushions very dense, bluish grey-green, up to 70 cm in diam. Branches tightly packed, very densely leafy, with cream-coloured marcescent leaves long persistent. Basal part of leaf suberect, distal part widely spreading, subspatulate-obovate, 4–7 mm long, 2–3 mm wide, covered with subsessile glands to 0.1 mm long, more sparsely so abaxially, margin entire (rarely slightly lobed at apex), apex obtuse to subacute. Inflorescence with a single sessile flower. Bract 1, oblanceolate, 4–5 mm long, c. 1 mm wide, base very shortly ciliate, margin entire or apically with a few minute denticles. Calyx 4–5 mm long, divided to ⅔-¾; lobes broadly lanceolate, often overlapping in basal ⅓, outside shortly glandular hairy, especially at base, on veins and on margin, inside sparsely glandular, base keeled, margin entire, apex subacute. Corolla yellow, glandular hairy, rather densely so toward base, less so apically, hairs 0.1–0.2 mm long; tube 20–24 mm long; limb c. 10 mm wide; lobes not or slightly overlapping, apex rounded or very slightly emarginate. Stamens in longstyled flowers inserted c. ⅔ from base; anthers c. 2 mm long. Ovary with 3 or 4 ovules; style in long-styled flowers conspicuously exserted; style in short-styled flowers c. ⅔ as long as corolla tube. Capsule broadly ovoid, c. 3 mm long, 3- or 4-seeded; valves thick, not twisted. Seeds 1.4-1.6 × 0.6-0.7 mm.

Phenology — Flowering in May, fruiting in June.

Distribution and ecology — Dionysia robusta is known from two localities in Ilam Province, Iran (Fig. 4). Each locality is a strip on the SE face of two parallel, deep gorges between 32°55′N, 47°18′E and 32°57′N, 47°22′E in an altitudinal range of 1550–1800 m. The type material was collected from the more northern strip. The species forms large subpopulations at both localities — not common for most species of this genus. The plants grow in crevices of vertical calcareous rocks and N-facing slopes. The general vegetation is dominated by Quercus brantii Lindl. accompanied by Acer monspessulanum L., Amygdalus orientalis Mill., Crataegus azarolus var. aronia L., Ficus carica sub sp. rupestris (Hausskn. ex Boiss.) Browicz and Pistacia atlantica Desf.

Fig. 2.

Dionysia robusta in its natural habitat — A, B: at anthesis; C, D: after anthesis. — All photographs taken at the type locality by S. Younesi; A, B: 11 May 2015; C, D: 15 June 2014.

Fig. 3.

A–G: Dionysia robusta — A: flowering branch; B–D: leaves; E: bract; F: calyx; G: corolla of short-styled flower; H: corolla of long-styled flower; I: fruit valve. — Scale bar: for A, G, H = 10 mm; for B–F, I = 5 mm. — Drawn by M. Lidén from part of the type material (Younesi 14494, IAUH).

Table 1.

Comparison of morphological characters of Dionysia robusta, D. gaubae, D. iranica, D. sarvestanica and D. tacamahaca.

Table 2.

Comparison of different bases in ITS DNA sequences of Dionysia robusta, D. gaubae, D. iranica, D. odora and D. sarvestanica. — Alignment length = 681 bases; each column represents a position with dissimilar bases.

Fig. 4.

Geographical distribution of Dionysia robusta, D. bornmuelleri, D. gaubae, D. iranica, D. odora, D. sarvestanica and D. tacamahaca in Iran and Iraq.

Conservation status — According to our observations, the number of mature individuals of Dionysia robusta is rather high (probably more than 10 000). We observed the population in two large localities in the form of two strips up to 10 km long and 400 m wide. The area of occupancy of D. robusta is less than 10 km². There is no information on population size reduction, but we project a decline in the area of occupancy, quality of habitat, and number of mature individuals due to recent severe droughts in the area. We suggest, therefore, that this species should be placed under the IUCN (2012) category Critically Endangered with the criteria CR B2ab(ii,iii,v).

Etymology — The epithet robusta refers to the robust habit and large size of the plants.

Comparison with other species — Dionysia robusta is easily distinguishable from other species growing in the region by having cushions very large, up to 70 cm in diameter, and leaves entire or slightly divided. It is similar to D. gaubae, D. iranica, D. sarvestanica and D. tacamahaca (Table 1). However, D. gaubae differs in having leaves longer and usually more divided, marcescent leaves strongly reflexed so as to become more or less coiled, glands on the leaves more clearly stalked, and calyx much more deeply divided. Dionysia iranica differs in its dark green colour, usually less dense habit, and more deeply divided calyx. Dionysia sarvestanica differs in having leaves not or only slightly spreading, smaller, and always entire, more densely glandular with hairs clearly stalked, and calyx divided to the base. Dionysia robusta is similar to D. tacamahaca in the outcurved leaves and distinct calyx cup, but is very different in indumentum.