Dionysias possess unique qualities that make them fascinating to both naturalists and botanists. They captivate us with their lovely appearance and amazing habitats, diverse range of species, considerable ornamental value, and remarkable capacity for producing new and cute varieties through cross-breeding (Zeraatkar et al., 2022; Lidén & Mehregan, 2023; Zeraatkar et al., 2023).

Many previous studies have shown that when two species of the genus are in sympatry and have overlapping flowering time, they often interbreed and create hybrids. This results in the formation of natural hybridization zones (Zeraatkar & Khajoei Nasab, 2022).

The occurrence of hybridization in Dionysia has been known for less than half of a century. To this point, only a small number of natural hybrids within the genus have been reported. In contrast, many artificially produced hybrids are commonly found in cultures (Lidén & Mehregan, 2023). The lack of natural hybrids produced within the genus is more likely because of strong pre-zygotic barriers to reproduction. Several species of the genus have restricted distributions, occupying only specific geographical locations. The distribution of suitable localities for many species is similar to that of islands, even occurring within a single mountain (Grey-Wilson, 1969).

In August 2021, during investigation on the genus Dionysia specimens kept at D herbarium, the first author came across specimens of D. iranshahrii Wendelbo and D. zagrica Grey-Wilson that have been collected from the same locality and attracted his attention. He speculated that the populations of these species might create another undescribed hybrid between purple and yellow-flowered species. Following our careful examination field in spring 2022-2024, we observed the two mentioned species occur side-by-side in nature and sometimes utilize the same habitats (under overhangs or on vertical faces and slopes), where diffuse hybridization zones with hybrid swarms can occasionally be witnessed between D. iranshahrii and D. zagrica.

Dionysia ×mallahiae Zeraatkar nothosp. nov. (= D. iranshahrii × D. zagrica) (Figs. 1-3)

Description: Cushions very dense green to bluish green, 5-10 cm across. Branches closely packed, densely clad with imbricate leaves. Yearly growth 2-4 mm, with contiguous leaf generations. Marcescent leaves brownish, brownish black, whitish, long persistent, eventually disintegrating and shed. Defoliated stems up to 1.5-2 mm in diameter, with a dark wine-red bark. Leaves green to bluish green, unnoticeably involute, slightly thick or papery, non-hyaline or hyaline at margin, lateral veins obscure or slightly raised, sclereids slightly significant or insignificant, conspicuously ciliate throughout with up to 0.2 mm long trichomes and short-stalked (0.05-0.1 mm long) and medium-sized (ca. 0.15 mm) glands; lanceolate, oblong-spathulate, oblanceolate, oblong, spathulate-lanceolate, elliptic-spathulate, spathulate or elliptic, 1.5-2.7(3) × 0.3-0.8(0.9) mm, abaxially and adaxially pubescent, glabrescent or glabrous, with trichomes to 0.2 mm long, short-stalked and medium-sized glands, apex acute, subacute, obtuse or sometimes rounded. Bracts 1 (0?), narrow, narrowly oblong to lanceolate, apex acute to obtuse, shorter than calyx, 1.5-2.5 mm long, pubescent like the calyx teeth. Flowers single, sessile. Calyx (2)2.5-3(3.5) mm long, divided for slightly more 1/2 to 4/5 of its length into oblong to lanceolate entire or with 1-2 fine teeth lobes, apex acute, ciliate along the margin, abaxially sparsely pubescent or glabrescent, adaxially glabrous sometimes with a few trichomes and glands at some teeth apex. Corolla pale/dark violet with a distinct yellowish eye; tube violet or pale yellow, 7-15 mm long, sparsely with trichomes to 0.2 mm long and short-stalked and medium-sized glands; limb (4)5-7(7.5) mm across, lobes elliptic, widely obovate, elliptic-obovate, suborbicular, apex entire (sometimes slightly emarginate), with a few trichomes and glands at the distal part of the lamina. Style of short-styled flowers up to 4-5 mm long, reaching about halfways through the tube; that of long-styled flowers 11-12 mm long, exserted or as long as the corolla tube. Anthers ca. 0.9 mm, inserted in the throat or just below the middle of the corolla tube. Ovary small, sub-spheric, with three ovules. Capsule narrowly ovate, valves spiraling after dehiscence, ca. 2.5 mm long, with seeds that lack embryos.

Type. Iran. Chaharmahal and Bakhtiari province. Felard district, near mount Dalankuh, 2810 m a.s.l., 24.IV.2022, Zeraatkar 7193 (holotype: D7193).

The specific epithet is chosen in honor of Dr. Mahlagha Mallah, an Iranian environmentalist and researcher who has made significant contributions to reduce environmental pollution in Iran. She is known as the founder of “Women’s Society Against Environmental Pollution”.

In the locality type, D. iranshahrii and D. zagrica start to flower at the beginning of middle of April and continues until the late of May. The flowering period of hybrid plants occur late of April to middle of May. The species are mainly pollinated by hawk moths such as Macroglossum stellatarum. It seems the hybrid is without seed production.

Dionysia iranshahrii with a very restricted distribution had been previously reported from two closely populations in Isfahan province at altitude 2400-2590 m a.s.l. (Lidén & Mehregan, 2023). In the framework of this paper, this species was collected for the first time from Chaharmahal and Bakhtiari province at 2810-2915 m a.s.l. (see Appendix 1). In contrast, D. zagrica is relatively widely distributed in the Chaharmahal and Bakhtiari province and south Isfahan at altitude 1850-2850 m a.s.l. (Lidén & Mehregan, 2023). Regarding pre-zygotic barriers (ecological isolation), there are only a few overlapping areas between D. iranshahrii and D. zagrica exist in the north of Felard district, at altitudes of 2810-2850 m a.s.l. (see Appendix 1). The hybridation between D. iranshahrii and D. zagrica do occur where the both species meet each other at their highest altitude (2800-3000 m a.s.l.).

Despite the differences in the niches of these species, their populations occasionally come into contact, which may result in interspecific hybridization (Table 1). One or two swarms of Dionysia × mallahiae grow at the hybridization zones where populations of D. iranshahrii and D. zagrica occur together. In agreement with previous studies in Primulaceae (Jacquemyn et al., 2009; Zeraatkar & Khajoei Nasab, 2022), the current results indicate such hybrid plants are in fact rare in nature and distributed within a narrow range between the parental habitats and do not spread further.

The parental plants remain morphologically distinct and pure in their hybridization zones. Previous studies in the genus demonstrate postzygotic isolation mechanisms still maintain parental species in the genus (Zeraatkar & Khajoei Nasab, 2022). Our observation shows that the following traits are variable among the hybrids: corolla color, corolla limb outline, leaf and calyx size, gland and trichome size, degree of prominence of lateral veins, thickness of leaf and calyx margin (Figs. 1-3, Table 1). Trichomes are totally absent in D. zagrica. In contrast, D. iranshahrii is densely covered by trichomes. The trichomes are present in the hybrid plants; however, they are considerably shorter in the hybrid plants than that of D. iranshahrii (Figs. 2-4, Table 1). D. zagrica is glandular pubescent all over while the glands are insignificant in D. iranshahrii. In our study, glands were present in the all hybrid plants but slightly longer compared with parental species (Figs. 2-4, Table 1). Across most of the investigated leaves, hybrids express patterns similar to D. zagrica.

The leaves of D. zagrica were described and illustrated as entire in previous research (Grey-Wilson, 1974; Lidén & Mehregan, 2023). More materials from broad geographic range demonstrate the leaves are entire and very rarely with 1-2 fine teeth in upper part or slightly lobed (Fig. 3B).

In contrast, in case of the reproductive traits, hybrids express patterns similar to the parents (Figs. 2 and 4, Table 1). The calyx lobes of D. iranshahrii are treated as entire in the original description and consequent studies (Wendelbo, 1975; Lidén & Mehregan, 2023). However, our materials show that the calyx lobes are mostly with 1-2 fine teeth (Fig. 3A). The ovule numbers are variable and range from 2-4 per ovary in the species.