Chorisochora (Acanthaceae) in Somalia: the new speciesC. chascanoides

Mats Thulin1,2, Iain Darbyshire3 & Hannah I. Banks4

Summary. The new species Chorisochora chascanoides is described from limestone cliffs in north-eastern Somalia.Three species were previously known in Chorisochora, two in Yemen (Socotra) and one in NE South Africa andBotswana. On morphological grounds the Somali species is believed to be most closely related to the two species onSocotra. The pollen of the new species is of the Ecbolium-type, in agreement with the other species ofChorisochora.

Key Words. Ecbolium, pollen morphology, taxonomy.

IntroductionThe account of the Acanthaceae for Flora of Somalia(Hedrén & Thulin 2006) comprised nearly 150species in 26 genera. In 2009 one of us (I.D.) founda specimen in the herbarium at Kew from northernSomalia (Newbould 1063), provisionally identified asMonothecium sp. nov. Monothecium Hochst. is a genusnot otherwise known from Somalia and this speci-men had not been consulted during the preparationof the Flora of Somalia account of the family.However, a closer investigation showed that thisspecimen cannot be a Monothecium, having, amongstseveral differences, bithecous rather than monothe-cous anthers. Instead, it represents a new speciesthat is best placed in the genus Chorisochora Vollesen.Chorisochora previously had three recognised species,two in Yemen (Socotra) and one in South Africa(Limpopo and Mpumalanga Provs.) and Botswana.The new species is described below.

Materials & MethodsThe description was compiled based upon the singleknown herbarium collection of Chorisochora chascanoidesheld at Kew. Herbaria known to house duplicatespecimens of Newbould collections were consulted forisotype specimens but no duplicates were uncovered.Due to the paucity of material, only a single floraldissection was made following soaking in Aerosol OT10% solution; all other measurements were made on

dry material. One anther of Chorisochora chascanoides wastaken from Newbould 1063, dissected to extract thepollen and mounted onto a SEM stub coated withdouble-sided sticky tape. The preparation was thensputter coated with platinum and examined using aHitachi S4700 cold field emission SEM at 2 kV.Palynological terminology follows Punt et al. (1994).

TaxonomyChorisochora chascanoides Thulin & I. Darbysh. sp.nov. differt ab omnibus speciebus generis foliismargine revolutis et floribus minoribus tubo corollaec. 4 mm (non 6 – 18 mm) longo et lobis corollae c. 5mm (non 10 – 25 mm) longis. Typus: Somalia, BariRegion, Assah, Newbould 1063 (holotypus K!).

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Shrublet, c. 30 cm tall; young stems terete or somewhat4-angled, brownish, densely puberulous with shorthairs, older stems glabrescent, up to c. 7 mm indiam. Leaves fairly thick and rigid; blade ovate toelliptic, 6 – 11 × 3.5 – 7 mm, rounded at the base,obtuse to subacute at the apex, with revolutemargins, 2 – 4 pairs of lateral veins prominentbeneath and network of finer veins often also visible,densely puberulous with short hairs on both surfaces;petiole 1 – 2 (– 4) mm long, puberulous. Inflorescenceraceme-like, 3 – 13.5 cm long including up to 0.8 cm

Accepted for publication January 2012.1 Department of Systematic Biology, EBC, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden. e-mail: mats.thulin@ebc.uu.se2 Honorary Research Fellow, Royal Botanic Gardens, Kew, Richmond, Surrey, UK.3 Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK. e-mail: i.darbyshire@kew.org4 Micromorphology Section, Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3DS, UK. e-mail: h.banks@kew.org

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Fig. 1. Chorisochora chascanoides. A habit; B leaf from below and with enlargement of margin; C portion of inflorescence withflower in situ; D bract (right) and bracteole (left); E calyx opened up and with enlargement showing indumentum; F corolla openedup, with stamens attached; G stamen with detail showing attachment of anther; H ovary and base of style; J tip of style; K valve ofcapsule; L seed. All from Newbould 1063. DRAWN BY MARGARET TEBBS.

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long peduncle; axis pubescent with spreading egland-ular and glandular hairs; bracts narrowly ovate toobovate, 3.5 – 4 mm long, densely pubescent withshort and long spreading hairs on both surfaces,subacute, with obscure venation, caducous. Flowersone per bract; pedicel c. 0.5 mm long; bracteoles 2,linear, 3 – 4 mm long, densely pubescent, caducous.Calyx divided almost to the base; lobes 5, linear, 4lobes subequal and 5 – 6.5 mm long, the ventral lobe3 – 3.5 mm long, all densely pubescent withspreading eglandular and glandular hairs. Corolla2-lipped, probably magenta, pubescent outside; tubec. 4 mm long, c. 1.5 mm wide, cylindrical, slightlycurved; lobes c. 5 mm long, becoming recoiled atanthesis; upper lip linear, of 2 fused lobes, entire;lower lip deeply divided into 3 linear lobes. Stamens 2,± parallel, held ± equidistant between upper andlower lip; filaments attached at the apex of thecorolla tube, c. 5 mm long, with short downwardlydirected hairs; anthers bithecous, medifixed, c. 2 mmlong, thecae oblong and attached at the same height,rounded at both ends; staminodes absent. Ovary4-ovulate, pubescent; style filiform, c. 9 mm long,pubescent in lower part; stigma minutely bilobed.Capsule club-shaped, flattened, c. 9 × 3 – 4 mm,pubescent, 2 – 3-seeded. Seeds flattened, broadlyelliptic in outline, c. 4 – 4.5 × 3 mm, shortly spinuloseall over and with a verrucose rim. Fig. 1.

DISTRIBUTION. Chorisochora chascanoides is known onlyfrom the type locality, situated in the Cal MiskaatRange in north-eastern Somalia. Cal Miskaat is well

known as an area with many narrowly endemic plantspecies, some examples from different families beingAcacia tephrophylla Thulin, Aloe miskatana S. Carter,Cyclamen somalense Thulin & Warfa, Fagonia gypsophilaBeier & Thulin, Haplophyllum sanguineum Thulin,Helianthemum speciosum Thulin, Jatropha miskatensisThulin, Plocama somaliensis (Puff) M. Backlund &Thulin, Polygala dasanensis Thulin, Scutellaria somalensisThulin, and Wellstedia robusta Thulin.SPECIMEN EXAMINED. SOMALIA. Bari Region: Assah,11°20'N, 49°49'E, fl. & fr. 5 Sept. 1957, Newbould 1063(holotype K!).HABITAT. Sheltered ravine in crack in limestone cliff; c.900 m alt.CONSERVATION STATUS. Known from a single specimen,this is probably a very local species that may beregarded as Critically Endangered (CR D1) followingthe categories and criteria of IUCN (2001). How-ever, at present there are no particular threats to thearea, which is without roads and has no permanentinhabitants.ETYMOLOGY. The epithet chascanoides chosen for thenew species refers to its habit, which is superficiallysimilar to various species of Chascanum E. Mey.(Verbenaceae), also found in rocky habitats in northernSomalia.NOTES. The genus Chorisochora was described byVollesen (1994) to accommodate three species, C. striata(Balf. f.) Vollesen (previously Ecbolium striatum Balf. f.),C. minor (Balf. f.) Vollesen (previously E. striatum var.minor Balf. f.), and C. transvaalensis (Meeuse) Vollesen(previously Angkalanthus transvaalensis Meeuse).

Fig. 2. Hydrated pollen grains of Chorisochora chascanoides (SEM), A equatorial view, B polar view; scale bars=20 μm. FromNewbould 1063.

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C. striata and C. minor are confined to Socotra, whereasC. transvaalensis, the type of the genus, is confined toNE South Africa and Botswana.

In the key to the genera of the Ecbolium grouppresented by Vollesen (1994), Chorisochora is distin-guished from Ecbolium Kurz (22 species in the OldWorld), Megalochlamys Lindau (10 species in Africaand Arabia) and Trichaulax Vollesen (one species inKenya and Tanzania) by having pedicellate flowersand corolla lobes longer than or about as long as thetube, and from Angkalanthus Balf. f. (one species onSocotra) by having erect inflorescences, linear-lanceo-late calyx lobes, a more or less cylindrical corolla tube,a deeply lobed lower lip of the corolla, and by havingstamens held more or less equidistant between thecorolla lips. The new Somali species fits the genericdescription of Chorisochora in all these respects,although the pedicels are only about 0.5 mm long(versus 1 – 2 mm in the three other species).

Daniel et al. (2008) included Chorisochora, togetherwith sampling of members of Angkalanthus, Ecbolium,Megalochlamys and Trichaulax, in a molecular studyfocusing mainly on the New World “Tetrameriumlineage”. However, the position of Chorisochora, repre-sented only by C. transvaalensis, was unresolved inrelation to these genera. Daniel et al. (2008) concludedthat “it is clear that understanding of Chorisochorarequires inclusion of the Socotran species in phyloge-netic work”. Pending this, we here accept the genuswith its original circumscription.

Chorisochora chascanoides seems to be most closelyrelated to its geographical neighbours, C. striata andC. minor on Socotra. These three species all differmarkedly from C. transvaalensis in southern Africa byhaving corolla lobes only slightly longer than the tube(not about twice as long as the tube), flowers inunbranched raceme-like inflorescences (not inbranched paniculate inflorescences), and by their smallcapsules (8 – 13 mm vs 15 – 22 mm long). However, C.chascanoides clearly differs from both C. striata andC. minor by its densely puberulous (not glabrous) stemsand leaves. Furthermore, C. chascanoides differs from allthe other species in the genus by its revolute leafmargins and small flowers (corolla tube c. 4 mm vs 6 –18 mm long and corolla lobes c. 5 mm vs 10 – 25 mmlong).

Pollen MorphologyDESCRIPTION. Shape subprolate, hydrated grains 35 – 46 ×34 – 37 μm, P/E ratio usually 1.1 – 1.2, amb circular inhydrated state, triangular in dehydrated state. Aperturesheterocolpate, 3-colporate with each colporus flanked

by two subsidiary colpi, one on either side of thecolporus; colpori slightly longer than subsidiarycolpi, extending into the apocolpium but not reach-ing the pole; colpi narrow, pore wider than width ofcolpus, broadly elliptic with longer axis orientedalong the same axis as the colpus. Sculpturingreticulate. Fig. 2.NOTES. According to Vollesen (1994) the pollen mor-phology of Angkalanthus and of the three species ofChorisochora then known is essentially identical to theEcbolium-type of pollen as described by Furness (1989).The pollen morphology of the new species describedhere is also of the Ecbolium-type and does not contradictthe placement of this species in the genus Chorisochora.It is of note that the genera Megalochlamys (Furness1989) and Trichaulax (Furness 1992) differ markedly intheir pollen morphology.

AcknowledgementsWe are indebted to Margaret Tebbs for the illustrationin Fig. 1. We thank Itambo Malombe for checking theholdings of Acanthaceae at EA for a duplicate of theNewbould specimen. We thank two anonymousreviewers for their comments on an earlier draft ofthe manuscript.

ReferencesDaniel, T. F., McDade, L. A., Manktelow, M. & Kiel, C.

A. (2008). The “Tetramerium lineage” (Acanthaceae:Acanthoideae: Jusiticieae): delimitation and intra-lineage relationships based on cp and nrITSsequence data. Syst. Bot. 33: 416 – 436.

Furness, C. A. (1989). The pollen morphology ofEcbolium and Megalochlamys (Acanthaceae). KewBull. 44: 681 – 693.

____ (1992). A note on the pollen of Trichaulaxmwasumbii (Acanthaceae: Justicieae). Kew Bull. 47:619 – 624.

Hedrén, M. & Thulin, M. (2006). Acanthaceae. In: M.Thulin (ed.), Flora of Somalia 3: 374 – 454. RoyalBotanic Gardens, Kew.

IUCN (2001). IUCN Red List Categories and Criteria:Version 3.1. IUCN Species Survival Commission.IUCN, Gland, Switzerland & Cambridge, UK.

Punt, W., Blackmore, S., Nilsson, S. & Le Thomas,A. (1994). Glossary of Pollen and Spore Terminology.LPP Contrib. Ser. 1. LPP Foundation, UtrechtUniversity.

Vollesen, K. (1994). Delimitation of Angkalanthus (Acan-thaceae: Justicieae) and the new genus Chorisochora.Kew Bull. 49: 469 – 479.

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