TAXONOMIC REVIEW AND PHYLOGENETIC INVESTIGATIONS OF LAVANDULA FROM IRAN AND OMAN

A review of the native Iranian species of Lavandula is presented, including the first recorded occurrence of L. pubescens , new distribution records for L. coronopifolia , and a detailed description and observations of the poorly known endemic L. sublepidota . The phylogenetic relationships of several taxa, including Lavandula sublepidota and L. hasikensis from Oman, are investigated for the first time using molecular data ( mat K and ITS regions), and changes to the sectional classification are proposed.


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Lavandula from Iran and Oman

Assessment of conservation status
The categories and criteria of the International Union for Conservation of Nature (IUCN, 2012) were used to evaluate threat levels for Lavandula species distributed in Iran. We used the occurrence data for our taxa in GeoCAT (GeoCAT, no date) to determine conservation priorities (Bachman et al., 2011).

Results
The recent phylogenetic analysis of Moja et al. (2016), based on the matK gene, provided the base tree to which we added Lavandula sublepidota and L. hasikensis (Figure 1). Although we were unable to amplify the entire gene region (1313 out of 1653 bp were amplified), the general topology of our tree and the grouping of the sections were similar to those in the previous study's tree. However, the proposed relationship between Lavandula sublepidota and L. hasikensis was not supported, with both species being within the Subnudae clade. The Bayesian analysis did suggest a relationship between Lavandula sublepidota and the Indian species L. bipinnata Kuntze (sect. Chaetostachys); however, this was with low support (posterior probability, 0.66). The phylogenetic tree placed Lavandula hasikensis close to L. samhanensis, with strong support (see Figure 1), their matK sequences being identical.
Although fewer ITS sequences were available, we carried out a molecular phylogenetic analysis to further elucidate relationships. This indicated a closer relationship between Lavandula hasikensis and L. dhofarensis than between the former and L. samhanensis, and as with the matK analysis, no close relationship between L. sublepidota and L. hasikensis (L. bipinnata was not sampled) ( Figure 2). The recently described Lavandula noorudinii (Patzelt & A.Al Hinai, 2019) was included in a molecular analysis for the first time, confirming its classification in sect. Subnudae.
Phenology. Flowers February to April, fruits March to May.
Distribution. Occurring from the Cape Verde Islands, across northern Africa, western Asia and the western Arabian Peninsula to southern Iran (Upson & Andrews, 2004). This is the most widespread distribution of any Lavandula species. In Iran, Lavandula coronopifolia was previously known from Hormozgan and Bushehr Provinces, and this study extends this to Kerman Province further to the east ( Figure 4).  Habitat and ecology. The distribution pattern of this species follows that of the Saharo-Arabian floristic region of Iran (Zohary, 1973). It typically grows on stony slopes, along river margins and at the edges of farms and cultivated areas (Jamzad, 2012).
Conservation status. Lavandula coronopifolia has an extent of occurrence (EOO) of 53,467 km 2 (an estimate based on previous records of this species; Jamzad, 2012) and an area of occupancy (AOO) of 3200 km 2 in Iran. It is treated as Near Threatened (NT) in Iran, and Least Concern (LC) globally.
Ethnobotany. No uses are recorded in Iran or elsewhere.   Recorded as Lavandula stricta in Flora Iranica (Rechinger, 1982) and Flora of Iran (Jamzad, 2012), the accepted name by priority is L. coronopifolia (Upson & Jury, 2002). The highly branched peduncles and long, often-interrupted, almost wispy flower spikes make this species readily recognisable (see Figure 3A,B). Its short bracts and calyx lobes of equal size are characteristic. This widespread species reaches its most easterly point of its distribution in Iran.  Description. See Upson & Andrews (2004).
Phenology. In Iran, flowers from February to October, curtailed by winter cold rather than drought stress. Inflorescences up to 10 cm long are common, bearing both flowers and fruit (see Figure 5D).
Distribution. Southwest Asia (Jordan and Palestine), Northeast Africa (Egypt, Eritrea), the Arabian Peninsula (Saudi Arabia and Republic of Yemen) and Iran (Bushehr Province).
Habitat and ecology. This species is found in the moist valleys on the northern slopes of Mount Khormoj and is known from two populations 5 km apart (see Figure 4). Here it is restricted to mesic environments in moist valleys on the northern slopes, which are recognised as part of the Saharo-Arabian floristic region (Zohary, 1973). One population grows on stony margins of date palm gardens and the other on rocky slopes and stony habitats accompanied by Mentha mozaffarianii Jamzad, a narrow endemic species previously recorded only from Hormozgan Province (Jamzad, 1987; see Figure 5A). It is clearly restricted to favourable microclimates away from the intense aridity typical of the area. Conservation status. During field observations, about 30 individuals were counted in two populations with an AOO of about 12 km 2 and an EOO of 0.05 km 2 . Lavandula pubescens is assessed as Critically Endangered (CR) in Iran [B1ac(ii+iii_iv)+B2ac(ii+iii+iv) + D] (IUCN, 2012). Its occurrence with the other restricted species strongly suggests that these habitats need protection. Globally, it is of Least Concern (LC) (Upson & Andrews, 2004).
Ethnobotany. This species' essential oil is composed largely of carvacrol, caryophyllene oxide, β-bisabolene, p-cymen-8-ol, β-caryophyllene, carvacrol methyl ether and terpinolene, and has shown notable antibacterial and antifungal activity (Chhetri et al., 2015;Ibrahim et al., 2017;Al-Badani et al., 2017). It has been the subject of many studies for its application in the production of palm oil (Rashed et al., 2016) and honey (Nuru et al., 2015). In Yemen it is used in folk medicine as a carminative, insect repellent and antiseptic (Chhetri et al., 2015). No uses are recorded in Iran, and based on fieldwork it is little known to local people. Lavandula pubescens is a well-known species notable for its acrid and unpleasant smell; it has a diagnostic indumentum with short-and long-stalked glandular hairs and long simple hairs. The pinnatisect leaves, which are highly dissected two or three times, are characteristic (see Figure 5B). It is a species of arid areas, as reflected in its woody rootstock and stem base from which annual stems are produced (Collenette, 1985;Upson & Andrews, 2004).
Its previously known distribution followed the Syro-African Rift Valley, with the species occurring on mountains and hills along the Red Sea coast and reaching the Dead Sea depression in the north. Its occurrence in Iran is significant due to the large disjunction across the Arabian Peninsula.  (Rechinger, 1979) and later in Hormozgan Province, Haji Abad, Shamil-e Bala, Bukhun, by Mozaffarian (Jamzad, 2012).

Lavandula sublepidota
Habitat and ecology. This species occurs on rocky limestone slopes with shallow soil on arid mountains (see Figure 6A,B). The areas of distribution in Darab (Fars) and Bukhun (Hormozgan) are the transitional area between the Irano-Turanian and Saharo-Arabian floristic regions (Zohary, 1973). It typically bears leaves around its base in spring (see Figure 6A), these subsequently dropping due to drought. Therefore it can appear leafless for parts of the year (see Figure 6B). Conservation status. According the AOO of 48 km 2 and EOO of 267 km 2 , Lavandula sublepidota is categorised as Endangered (EN) [B1ac(ii+iii+iv) + B2ac(ii+iii+iv) + D] (IUCN, 2012). During recent exploration of the area, only a single individual was recorded at the type locality (see Figure 4). This previously poorly known species was described by Rechinger (1979) during work on Flora Iranica and based on specimens collected in the Zagros Mountains in the Province of Fars, south Iran. The scale-like adpressed stem hairs, reflected in the epithet, are unique and give the species its characteristic whitish appearance. Rechinger (1979) originally placed the species in sect. Pterostoechas and noted affinities to Lavandula coronopifolia (treated as L. stricta). Although it bears single-flowered cymes, these are spirally arranged in Lavandula sublepidota rather than decussate, as is diagnostic for sect. Pterostoechas. Its sectional affinities therefore lie elsewhere and are discussed further below.

Biogeography and the flora of Iran
Both Lavandula pubescens and L. coronopifolia reach their most easterly distributions in Iran. Of particular note is the strong disjunction of Lavandula pubescens between its main distribution centre along the Syro-African Rift Valley and Iran. Such disjunct distribution patterns are known in other Lavandula species, including L. multifida L., a western Mediterranean species with disjunct populations in Sicily and Egypt, and L. dentata L., also western Mediterranean but with a disjunction to the mountains of Yemen and Saudi Arabia. Rather than being a result of recent dispersal events, these distributions most likely reflect a previously much wider occurrence and subsequent range contraction due to post-glacial climate change and the increasing desiccation of the Sahara and adjacent regions over the past 5000 years (Upson & Andrews, 2004). The current occurrence of Lavandula pubescens in mesic environments in Iran supports such a relictual distribution. Although Lavandula coronopifolia has a widespread distribution, its actual occurrence across its range is associated with mid-altitude mountain ranges and desert wadis, which is reflected in its scattered distribution in Iran. Section Subnudae is characterised by many narrow endemic species usually associated with mountain ranges. This pattern is reflected in the distribution of Lavandula sublepidota.

Sectional relationships
In the most recent taxonomic monograph by Upson & Andrews (2004), it was noted that Lavandula sublepidota, with single-flowered, spirally arranged cymes, could be assigned to sections Subnudae, Chaetostachys or Hasikenses rather than to sect. Pterostoechas (Rechinger, 1979). The general morphology, major differences in the nutlet and restriction of distribution to India is not consistent with its placement in sect. Chaetostachys, although a relationship with low support is suggested here.
Lavandula hasikensis, a narrow endemic from the Dhofar mountains in Oman, was described by Miller (1985), who noted the spirally arranged cymes, subequal calyx lobes and geography suggesting affinities with sect. Subnudae. Key differences were the distinctive double-lobed bracts, flower stalks extending in fruit and the habit of a woody subshrub (rather than a woody perennial), but it was not assigned to a section. Upson & Andrews (2004) created sect. Hasikenses, recognising the differences observed by Miller (1985), and included Lavandula sublepidota based on the photograph and description in Flora Iranica (Rechinger, 1982). This specimen showed bracts with the distinct wing-like membranous lobes, short central apex and capitate spikes extending in fruit.
The availability of new herbarium collections of Lavandula sublepidota has since resulted in the interpretation of these characters being questioned. The bracts are consistently scarious with a long-acuminate apex, and although the bases are broad, they are not lobed. The availability of a high-quality scan of the type also shows the bracts to be less distinctly lobed than they appear in the photograph in Flora Iranica. It is possible to interpret the fruiting axis as extended.
The molecular data and phylogenetic analysis presented here has provided independent evidence of its affinities. Both sequence regions show Lavandula sublepidota embedded in the clade corresponding to sect. Subnudae. With reinterpretation of morphological characters based on new material, we hereby transfer Lavandula sublepidota to sect. Subnudae.
Our molecular data and increased sampling provide some intriguing new insights. The trees show Lavandula hasikensis embedded in sect. Subnudae, close to L. samhanensis, based on the matK region, and L. dhofarensis in the ITS tree. All three species are native to the escarpment mountains of Dhofar. It could be argued that Lavandula hasikensis should also be included in sect. Subnudae. However, the key morphological characters, such as bract morphology, noted by Miller (1985) would be inconsistent with other members of the section. We also note that sections Subnudae, Chaetostachys or Hasikenses share the spirally arranged cymes, a unique character in the genus. One possible treatment would be to merge all three into sect. Chaetostachys Benth., because this is the oldest name. However, this treatment would ignore some major morphological differences, and differences in chromosome number and nutlet morphology. The transfer of Lavandula sublepidota renders all three sections consistent and communicates useful information on geography and morphology, hence we retain these three sections.