New taxa of Barleria sect. Prionitis (Acanthaceae) from the Horn of Africa biodiversity hotspot in Somalia

. Two new taxa in Barleria L. sect. Prionitis Nees (Acanthaceae) are described from Somalia, namely Barleria biramosa Defty & I.Darbysh. from central Somalia and B. compacta Malombe & I.Darbysh. subsp. minima I.Darbysh. & Defty from the north-east coastal region. These taxa are further endemics of the Horn of Africa biodiversity hotspot and have highly restricted ranges. Barleria biramosa was previously included within B. punctata Milne-Redh., another range-restricted endemic of the Horn of Africa region form northeast Ethiopia and northern Somalia; an updated description of B. punctata is therefore provided. Notes on the habitat requirements and conservation status (extinction risk) of the species are provided. Barleria biramosa is considered to be globally Endangered whilst B. compacta subsp. minima is currently assessed as Least Concern; the published assessment of Vulnerable for B. punctata is confirmed. With these additions, 11 taxa in 10 species of Barleria sect. Prionitis are currently recognised in Somalia.


INTRODUCTION
The Horn of Africa biodiversity hotspot-one of only two entirely arid biodiversity hotspots globally-ranges across the drylands of northeast continental Africa, the southern Arabian Peninsula and the Socotra archipelago.It covers most of Somalia, Djibouti, parts of Ethiopia, Eritrea, Kenya, Yemen and Oman, and a small portion of northeastern Sudan (CEPF 2024).This hotspot is particularly important for its rich endemic flora, with many plant species having highly restricted ranges (Thulin 2004;Friis et al. 2005;Marshall et al. 2016;CEPF 2024).For example, in Somalia, Thulin (2006a) reports a total flora of 3,165 species, of which approximately 800 (25%) are endemic.
Northeast Africa in general, and in particular the Horn of Africa hotspot, is amongst the most diverse areas globally for the Acanthaceae family (Manzitto-Tripp et al. 2022).For example, in the speciesrich genus Barleria L. (Acanthaceae: Acanthoideae: Barlerieae; Manzitto-Tripp et al. 2022), 32 species are known from Somalia alone, 12 (37.5%) of which are endemic (numbers modified from POWO 2024), this representing over 10% of the total species richness in Barleria.Several of the endemic species from this region have been described relatively recently, including B. albomarginata Hedrén, B. compacta Malombe & I.Darbysh., B. dentata Hedrén, B. ensermui (Hedrén 2006a; Malombe and Darbyshire 2010;Ensermu and Darbyshire 2018).Many are known from few botanical collections, and B. ensermui and B. ilicifolia are both known only from the type collections, despite being showy, large-flowered species.Hence, the likelihood of further new discoveries in Barleria within this region is high, particularly as large areas remain under-explored botanically.
However, the Horn of Africa is one of the most degraded biodiversity hotspots in the world due to overgrazing, charcoal production, political instability and infrastructure development (Thulin 2004;CEPF 2024).Therefore, it is important that the endemic species of the region are identified and described in light of the high levels of threat faced in this region and the urgent need for effectively targeted conservation efforts.
As part of a planned monograph of Barleria, two interesting taxa within sect.Prionitis Nees that have come to light amongst herbarium specimens from Somalia are here investigated morphologically for their taxonomic status.The first is a taxon from central Somalia that has been previously included within Barleria punctata Milne-Redh.by Hedrén (2006b) in the Flora of Somalia treatment of Barleria.That species is otherwise known only from northern Somalia and northeast Ethiopia, and is disjunct from the central Somalian populations both geographically and ecologically.The second taxon is from arid coastal northeast Somalia and is closely allied to Barleria compacta Malombe & I.Darbysh., described in 2010 from the same region, although with most collections from further inland (Malombe and Darbyshire 2010).

MATERIALS & METHODS
Herbarium specimens of the potential new taxa and morphologically allied species housed at EA, ETH, FT, K and UPS herbaria were analysed and measured at K, using standard herbarium practices; herbarium abbreviations follow Thiers (updated continuously).Prior to dissection, flowers were soaked in Aerosol OT 5% solution; all other characters were measured on dry material.All duplicates seen by the authors are marked "!".Barcodes for duplicates are listed wherever available to facilitate digital access to the specimens.
The distribution map for the relevant taxa was produced in QGIS V.3.2, using georeferenced herbarium collections.Country borders and first-order administrative boundaries were downloaded from GADM (https:// gadm.org/maps.html).
The species conservation (extinction risk) assessment follows the Categories and Criteria of the IUCN Red List (IUCN 2012) and the guidelines for their use (IUCN Standards and Petitions Subcommittee 2022).Extent of Occurrence (EOO) and Area of Occupancy (AOO) were calculated using the GeoCAT tool (https:// geocat.iucnredlist.org/;Bachman et al. (2011).

RESULTS
Following detailed morphological investigation, two new taxa are described in the taxonomic account below.As noted in the Introduction, the first of these, Barleria biramosa Defty & I.Darbysh., was previously included in the circumscription of B. punctata by Hedrén (2006b).Whilst B. biramosa is superficially similar to that species, it differs in a number of vegetative and floral traits and the two are readily separable as well as being geographically and ecologically disjunct.As the description of B. punctata by Hedrén (2006b) includes specimens of B. biramosa, we also provide a full, modified description of B. punctata s.s. in the Taxonomic Account below.
The second new taxon is closely allied to Barleria compacta Malombe & I.Darbysh., described in 2010 from the same region, although with most collections from further inland (Malombe and Darbyshire 2010).In fact, one of the specimens now assigned to the new taxon was originally included among the paratypes of B. compacta.They differ primarily in vegetative characters and have very similar floral morphology and so they are treated as subspecies, with the new taxon B. compacta subp.minima I.Darbysh.& Defty described below.
Together with other taxonomic changes made after the Flora of Somalia account (Hedrén 2006b), i.e., the description Barleria polhillii I.Darbysh.and the reduction of B. glaucobracteata Hedrén to synonymy within B. quadrispina Lindau by Darbyshire et al. (2010) 1).

Diagnosis
Barleria biramosa has previously been confused with B. punctata but differs in (1) the axillary spines having a stalk 5.5-13 mm long with similarly sized spine rays (versus stalk 1.5-3.9mm long, usually shorter than the spine rays, up to 5× shorter); (2) the leaf indumentum including unequally biramous hairs (versus hairs all simple, uniramous); (3) the calyx having broad sessile glands on the median portion of the anterior and posterior lobes either side of the midrib (versus no visible glands); (4) the offset of the abaxial lobe relative to other lobes being 8.9-10.6 mm (versus 4.7-5.9mm); (5) the abaxial corolla lobe shape being lanceolate and 5.8-6.5 × 1.6-1.8mm in size (versus broadly obovate and 12.2-12.3× 8.5-9.5 mm in size); (6) the ratio of the abaxial: lateral corolla lobes length being ca.0.4: 1 (versus 0.88-0.91:1); and (7) the flowers being held in the distal portion of the branches but the bracts barely differentiated from leaves (versus flowers held in a short terminal spike with the bracts clearly differentiated from the leaves).See Table 1.

Etymology
The species epithet "biramosa" denotes the unequally biramous hairs, present on the foliage, that are unusual in Barleria sect.Prionitis; this is one of the key characters for separation of this species from Barleria punctata.

Conservation status
Based on current evidence, this species is highly range-restricted, with an area of occupancy (AOO) of 8 km 2 ; the extent of occurrence (EOO) based on application of a minimum convex polygon is less than 1 km 2 , hence EOO is matched to AOO at 8 km 2 in accordance with the IUCN guidelines.This species occurs in deciduous bushland, where overgrazing by goats and use of wood for firewood, charcoal burning and house building pose some threat (M.Thulin, pers. comm. 2024).There is some habitat degradation and human activity observable on Google Earth imagery in the immediate vicinity of Yasoomman village.Agricultural activity is also present along the river valley to the west of the escarpment.Based upon this information, two threat-based locations are defined.These threats are inferred to result in a continuing decline in extent and quality of habitat and, combined with its small EOO and AOO, this species is assessed as Endangered (EN) under criterion B1 and B2: EN B1ab(iii)+2ab(iii).

Taxonomic notes
Although this species has been previously confused with B. punctata, and this is the most likely species with which B. biramosa could be confused, the two are readily separated by the characters listed in the diagnosis and Table 1.The biramous hairs on the leaves are an unusual character in B. biramosa; such hairs are more frequent in Barleria sect.Somalia (Oliv.)Lindau, where they can be equally biramous to anvil-shaped, i.e., with one well-developed branch and a second, poorly developed or stunted branch (Balkwill and Balkwill 1997;Darbyshire et al. 2010).Within sect.Prionitis, unequally biramous hairs have otherwise been recorded in B. brevispina (Fiori) Hedrén, another species of the Horn of Africa biodiversity hotspot.That species also shares with B. biramosa the highly zygomorphic corolla with a strongly offset and much-reduced abaxial lobe relative to the other lobes.These two species may therefore be allied, and B.brevispina is included in Table 1 for completeness.However, B. brevispina is easily separated from B. biramosa in, amongst other differences, having only shortly-stalked (0.5-3 mm) axillary spines, the sessile glands on the leaves, bracts and (usually) calyx being absent or sparse and inconspicuous and having smaller anthers, 2.5-3.3 mm long.Most populations of B. brevispina are additionally most easily separated by having linear-lanceolate to narrowly oblong leaves with a length: width ratio 5.5-15.5: 1 and so markedly different from those of B. biramosa.However, there are a few specimens of B. brevispina with broader leaves, notably P.E.Ellis 226 (K! [K001295268]) from SW of El Rago in eastern Ethiopia where the leaves are more elliptic or obovate (length: width ratio ca.2.4-2.7:1), similar in shape to those of B. biramosa.That specimen is, however, otherwise a good match for B. brevispina.
Ipomoea hiranensis Thulin has a similar distribution to B. biramosa in the Buloburde District of Hiiraan, with the type specimen (M.Thulin & Abdi M. Dahir 6488, holotype UPS, isotype K) from the same escarpment above Yasoomman as the type of Barleria biramosa (Thulin 2008).

Habitat & Ecology
This species occurs on rocky slopes and ridges associated with mountain valleys and on open stony ground, sometimes associated with limestone, at 884-1524 m asl.

Conservation status
This species is assessed as Vulnerable under criteria B: VU B1ab(iii)+2ab(iii) on the IUCN Red List (Darbyshire and Roberts 2023).It has an extent of occurrence of 12,915 km 2 , an area of occupancy of 28 km 2 and is known to occur in seven locations.The major threat to this species is overgrazing by livestock, exacerbated by drought, and there is an inferred resultant continuing decline in area, extent and quality of habitat.

Taxonomic notes
The type specimen and the single specimen seen from Ethiopia-the two western-most collections-differ notably from the other material in having ovate calyx lobes 3-4.5 mm long (versus lobes lanceolate-acuminate, 5-9 mm long); minute to small, ovate to linear-lanceolate bracteoles, 1.2-6.7 × 0.6-0.8mm (versus larger, always linear-lanceolate, 9.3-11.5 × 1.1-1.6 mm) and proportionately broader bracts with a shorter apical spine, 2.5-3.2mm long (versus spine 3.4-4.9mm long).Two subspecies may well be involved but it is desirable to see more material before drawing firm conclusions.
Barleria punctata is superficially similar to the more widespread species B. proxima but differs most clearly in having glabrous, not puberulous, corollas and capsules, in having more sparsely hairy calyces, those of B. proxima being strigose throughout externally, and in having a larger and broader abaxial corolla lobe, that of B. proxima being only 3-4.5 mm wide (measurements for B. proxima from Darbyshire et al. 2010).

Diagnosis
Subsp.minima differs from subsp.compacta in (1) the axillary spines having a stalk 7-15.5 mm long and usually longer than the spine rays (versus (0.8-)1.5-5 mm long, usually shorter than the spine rays and up to 3-5× shorter); (2) the leaves being shortly oblong-elliptic or somewhat obovate (versus leaves linear, linear-lanceolate or narrowly oblong); (3) the flowers being subsessile (versus flowers usually on a peduncle 1.5-8 mm long, rarely subsessile); and (4) the anterior and posterior calyx lobes being lanceolate, with a gradually tapering apex that is not acuminate (versus anterior posterior calyx lobes lanceolate-acuminate).See Table 2.

Distribution
Occurs in the coastal region of northeastern Somalia in Bari Region, in the vicinity and north of Bandarbeyla town (N3 floristic region).(Figure 2).

Habitat & Ecology
Habitat information for this subspecies is very limited, with the three early (non-type) collections lacking any habitat notes; J.B. Gillett recorded it occurring on a limestone plateau with low sparse Acacia-Commiphora bushland and scattered Dobera glabra at the type locality.However, it has been noted that the habitat along the coast north and south of Bandarbeyla is composed of mostly bare rocks and sand with sparse vegetation, whereas the plateau a bit further inland has a vegetation of scattered low bushes (M.Thulin pers.comm.2024).It is recorded from ca. 60-240 m asl (220 m recorded on Gillett 23105).

Conservation status
This subspecies has a restricted range, with an extent of occurrence (EOO) of 38 km 2 and an area of occupancy (AOO) of 16 km 2 based on known occurrence data.It was recorded as "occasional" at the type locality but no other notes on abundance are available.It is not known from any protected areas, but this species occurs in habitat that is mostly undisturbed by human activity.Despite having no or few permanent inhabitants, apart from in Bandarbeyla itself, the area north and south of the town would be visited after rain by nomads or people coming to fish during certain periods of the year -the latter mainly affecting the coastal strip only (M.Thulin, pers. comm. 2024).With no confirmed threats, this subspecies is assessed as Least Concern (LC), but threats should be assessed more completely and monitored as any increase in disturbance may quickly cause this subspecies to become Vulnerable.
Subsp.compacta was also assessed previously as of Least Concern (LC) by Malombe and Darbyshire (2010) and therefore the species as a whole, including the two subspecies now recognised, is considered to be LC.

Taxonomic notes
In the protologue of Barleria compacta, Malombe and Darbyshire (2010) noted that Gillett 23105 (EA) from west of Bandarbeyla in NE Somalia was allied to that new species but differed in the longer stalks to the spines, the shorter and more elliptic or shortly oblanceolate, conspicuously glaucous leaves, and subsessile flowers.The Gillett specimen was therefore excluded from B. compacta, although a specimen with similarly shaped leaves (Merla, Azzaroli & Fois s.n.ex Migiurtinia, Altipiano presso Culule, FT) was included among the para- Detailed study of these four specimens has revealed that this taxon is indeed close to Barleria compacta in the compact growth habit, axillary single-flowered cymes, and a subregular corolla with the abaxial lobe barely offset from the other lobes and comparable in size.However, they differ in the characters noted in the Diagnosis above.The rank at which to separate these two taxa is debatable, and they may ultimately prove to be separate species, but given their floral similarity and the fact that some of the differences (e.g., whether or not the flowers are pedunculate) are not entirely diagnostic, we consider subspecies rank to be most appropriate based on current evidence.These two taxa appear to be largely allopatric, with subsp.minima occurring close to the Indian Ocean coastline and subsp.compacta occurring more inland except for one coastal locality to the south of the known range of subsp.minima.
The glaucous leaves of the type specimen are very striking and differ from the typically brighter green leaves of subsp.compacta.However, the Merla et al. collections are less markedly glaucous and there is some overlap between the leaf coloration on these specimens and on some specimens of subsp.compacta (e.g., T. Fison 25, K!).Some of the characters observed in subsp.minima, notably the compact habit, long-stalked spines and short leaves, are reminiscent of Barleria tetracantha Balf.f., a species that is endemic to the Socotra (Soqotra) archipelago of Yemen.There are some phytogeographic links between northeast Somalia and the Socotran flora, rather unsurprisingly given that Socotra lies only ca.350 km from the Somali coastline.For example, in Acanthaceae, the Bandarbeyla area is the only known locality in continental African for Rhinacanthus scoparius Balf.f., a species previously thought to be endemic to Socotra (Miller and Morris 2004;Thulin 2006b).However, B. compacta, including subsp.minima, differs from B. tetracantha in having markedly larger flowers particularly with regard to the corolla lobes, with the abaxial lobe slightly offset from the other lobes (so less strictly salverform than in B. tetracantha), larger anthers and always having singleflowered cymes.For completeness, the Barleria compacta subsp.minima is compared to both B. compacta subsp.compacta and B. tetracantha in Table 2.In the published RADseq phylogeny of Barleria (Comito et al. 2022), B. tetracantha is resolved as sister to a clade comprising B. compacta s.s. and B. brevispina (Fiori) Hedrén, the latter two species forming a morphological "species pair" which are almost inseparable in the vegetative and fruiting states but have very different corolla morphology, B. brevispina being highly zygomorphic with a much reduced and offset abaxial lobe (Malombe and Darbyshire 2010).
I.Darbysh.,B. ilicifolia Hedrén and B. shebelleensis Ensermu & I.Darbysh.from Somalia, and B. gidoleensis Ensermu & I.Darbysh.,B. ferox Ensermu & I.Darbysh.and B. negeleensis Ensermu & I.Darbysh.from Ethiopia , this work results in 10 species and 11 taxa being recognised within Barleria sect.Prionitis in Somalia at present.However, there is still further taxonomic work needed on this group in the Horn of Africa biodiversity hotspot, particularly in relation to the variable species B. proxima Lindau and B. quadrispina, which are currently under investigation.

Table 1 .
A comparison of the diagnostic characters for separation of Barleria biramosa from Barleria punctata and Barleria brevispina.New taxa of Barleria sect.Prionitis (Acanthaceae) from the Horn of Africa biodiversity hotspot in Somalia

Table 2 .
A comparison of the diagnostic characters for separation of Barleria compacta subsp.compacta, Barleria compacta subsp.minima and Barleria tetracantha.This latter specimen had only been seen as a digital image at the time of the publication of B. compacta and so measurements and detailed observations were not taken from Merla et al. s.n.when preparing that description.A recent visit to the FT herbarium by one of us (I.Darbyshire) allowed for more detailed investigation of this specimen and also revealed two further collections by Merla et al. that match Gillett 23105.