BS 55 315

Diversity and endemism of the westernEthiopian escarpment – a preliminary

comparison with other areas of the Horn of Africa

SEBSEBE DEMISSEW, INGER NORDAL, CHRISTOF HERRMANN, IB FRIIS,TESFAYE AWAS AND ODD STABBETORP

SEBSEBE DEMISSEW, NORDAL, I., HERRMANN, C., FRIIS, I., TESFAYE AWAS & STABBETORP, O. 2005. Diver-sity and endemism of the western Ethiopian escarpment – a preliminary comparison with otherareas of the Horn of Africa. Biol. Skr. 55: 315-330. ISSN 0366-3612. ISBN 87-7304-304-4.

The vegetation on the western Ethiopian escarpment is still fairly intact, but imperfectly known.The escarpment-area agrees with the area of White’s Undifferentiated woodlands (Ethiopian type). Ithas characteristic vegetation, which consists mainly of deciduous woodland, with combretaceoustrees, e.g. Anogeissus leiocarpus, Combretum hartmannianum, or the frankincense tree, Boswelliapapyrifera, and dense thickets of the lowland bamboo Oxytenanthera abyssinica. Other vegetationtypes are wooded grassland, riverine forest and swamps. Potential threats to the vegetation andflora of the western escarpment are mentioned. The flora of the western escarpment consists ofat least 950 species, of which at least 27 are endemic or near-endemic. Most of these occur in theBenshangul Gumuz National Regional State, a core area of the western Ethiopian escarpment. Anumber of new endemic species have been discovered in Benshangul Gumuz in recent years,especially petaloid monocots. Genera with western escarpment endemics include Ceropegia(Asclepiadaceae), Vernonia, Bidens and Laggera (Asteraceae), Combretum (Combretaceae), Crinum(Amaryllidaceae), Chlorophytum (Anthericaceae) and Aloe (Aloaceae). With regard to diversitythe western escarpment ranks at a low position when compared with Ethiopian and EritreanFlora regions, while with regard to number of local endemics it ranks higher than most Ethiopianand Eritrean Flora regions, but lower than Flora regions in Somalia. With regard to the relativenumber of local endemics the western escarpment ranks lower than nearly all Flora regions inSomalia, but higher than nearly all Ethiopian and Eritrean Flora regions. Possible reasons for thedevelopment of the endemism in a transition zone between the Nile Valley and the Ethiopianhighlands are discussed. The new endemic species Chlorophytum herrmannii Nordal & Sebsebe andChlorophytum serpens Sebsebe & Nordal from the region are described in an appendix, and thenew combination Drimiopsis spicata (Baker) Sebsebe & Stedje for an endemic species is made.

Sebsebe Demissew, National Herbarium of Ethiopia, Addis Ababa University, P.O. Box 3434, Addis Ababa,Ethiopia. E-mail: nat.heb@telecom.net.et or sebsebed@bio.aau.edu.et

Inger Nordal, Department of Biology, University of Oslo, P.O. Box 1045, Blindern, N-0316 Oslo, Norway. E-mail: inger.nordal@bio.uio.no

Christof Herrmann, Av. Industrial 2, Satipo, Peru. E-mail: c_herrmann62@hotmail.com

Ib Friis, Botanical Garden and Museum, Natural History Museum of Denmark, University of Copenhagen,Gothersgade 130, DK-1123 Copenhagen K, Denmark. E-mail: ibf@snm.ku.dk

Introduction

The study of the Ethiopian flora of vascularplants has intensified since the beginning ofthe Ethiopian Flora project in 1980 and muchnew herbarium material has accumulated(Friis 2001). Yet, the gathering of informationand the scientific investigations in the differentparts of Ethiopia have not been evenly distrib-uted. Accessible regions with passable roadsand other infrastructure have been betterinvestigated than those without these facilities.The construction of new roads, particularly inthe southern regions of Ethiopia, has resultedin records of species that are either new to sci-ence or new for the Ethiopian flora. However,many other areas remain poorly collected(Friis 2001).

The western escarpment of the Ethiopianhighlands is one of the areas that have had lit-tle attention before 1980. The flora around thetwin towns of Gallabat and Metemma on theSudan-Ethiopian border was studied in 1865(Fig. 1 and the section Exploration of the flora inthis paper) and this and a few other areas ofthe western escarpment, especially in the Gam-bella National Regional State (Fig. 1), havebeen visited by a number of botanists since.

The vegetation of the western Ethiopianescarpment has been characterised as a sepa-rate vegetation unit by White (1983) on hisvegetation map of Africa, where it is mapped asunit no. 29b (Fig. 1) and named Undifferenti-ated woodlands (Ethiopian type). To the east, thisparticular vegetation type is bordered by theextremely mixed and complex vegetationmosaic of the Ethiopian highlands, to the west

with the grassland, wooded grassland andbushland of the Nile Valley. This area has alsoappeared, and has been somewhat differentlytreated, in other recent attempts at mappingthe Ethiopian vegetation (Friis & SebsebeDemissew 2001), but White’s concept seems tous to be the most appropriate.

Our preliminary analyses of what we know sofar about this little explored region, includingdata which we have extracted from the Flora ofEthiopia and Eritrea (Hedberg & Edwards 1989,1995; Edwards et al. 1995, 1997, 2000), showthat this region has an interesting and partlyunique flora.

There is very little detailed informationabout the environment of this area, but what issaid in the following, based primarily on gov-ernment reports and a project survey of theBenshangul Gumuz National Regional State(Population and Housing Census of Ethiopia1994; Bureau of Planning and EconomicDevelopment 1998; Feasibility Study 2001),may be approximately true for large parts ofthe western Ethiopian escarpment. The centralposition of the Benshangul Gumuz NationalRegional State is indicated in Fig. 1.

The aim of this paper is to demonstrate theendemism of the western Ethiopian escarp-ment and to illustrate the general interest ofthe flora of that area, where comparativelymuch of the natural vegetation is still nearlyintact. By doing so, we hope to encourage fur-ther studies as the area becomes more gener-ally accessible. We also sincerely hope that anincreasing knowledge of this area might con-tribute to the conservation of the vegetationand flora of this interesting area.

316 BS 55

Tesfaye Awas, Institute of Biodiversity Conservation and Research, P.O. Box 30728, Addis Ababa, Ethiopia

Odd Stabbetorp, Norwegian Institute for Nature Research, P.O. Box 736, Sentrum, N-0105 Oslo, Norway. E-mail: odd.stabbetorp@nina.no

Physical environmentThe topography of the western Ethiopianescarpment is characterised by a rolling ter-rain, sloping sometimes comparatively gently,sometimes dropping steeply from an averageof ca. 1800 m (sometimes considerably higher)on the Ethiopian highlands to the east to 500-700 m in the lowlands of the Sudan. In the low-land there are a number of isolated hills andoutcrops rising several hundred meters abovethe prevailing elevation.

The exact area of the western Ethiopianescarpment is not known, but the area ofWhite’s Undifferentiated woodlands (Ethiopiantype) is approximately 145,000 km2, when esti-mated from the vegetation map accompanyingWhite (1983).

The average rainfall (more or less unimodalfrom April to October, sometimes with smallpeaks in January to February) is 1200 mm inthe area around the town of Assosa, capital ofthe Benshangul Gumuz National RegionalState, and this figure is reduced towards northand west to about 800 mm. There are heavyshowers associated with thunderstorms overthe escarpment (oreographic rain). The meanannual temperature varies from 20º C to 35º C,and the variation is, as elsewhere, strongly cor-related with altitude.

The geology of the area comprises predomi-nantly outcrops of very old Precambrian rocks.Deep clayish red soils (dystric nitosols) pre-dominate in most of the zone south of the BlueNile (Abay) river. These have good physicalproperty with general agricultural potential.North of the Abay, the predominant soils(orthic acrissols) are chemically poorer andhave a more limited agricultural potential,although big farms with good potential havebeen established at the base of the westernescarpment near the border between Ethiopiaand Eritrea. The soils in many places south ofthe Benshangul Gumuz National RegionalState seem also to have more limited agricul-

tural potential. Particularly in the BenshangulGumuz National Regional State the westernPrecambrian formation holds rich mineraldeposits, mainly gold, but also copper, lead,and zinc. In addition there are importantoccurrences of marble, which to some extentare utilised.

Vegetation; species richnessOn the western escarpment of Ethiopia thedestruction of forest and woodland resourceshas been less than in other parts of Ethiopia.This is due to the low population density andthe general inaccessibility of the region. Mostof the region is covered with different types offorests, woodlands and bamboo tickets.

The common woodland type is dominatedby small to moderately sized trees with fairlylarge deciduous leaves. The woodland has anumber of floristic characteristics, that havepartly been listed by White (1983, p. 107) in hisdescription of the Undifferentiated woodlands(Ethiopian type). Later, but mainly unpublishedstudies (described in more detail below underExploration of the Flora), have supplemented thisinformation. Species of Terminalia, Combretum,and Lannea are common, as well as Entadaabyssinica, Erythrina abyssinica, Strychnos innoc-ula, Anogeissus leiocarpus, and Stereospermum kun-thianum. Particularly interesting is the com-mon occurrence of the solid-stemmed lowlandbamboo (Oxytenanthera abyssinica). The groundcover is a tall stratum of perennial grasses,including species of Cymbopogon, Hyparrhenia,Echinochloa, Sorghum and Pennisetum. This vege-tation type, which occurs at most altitudes ofthe escarpment, is burnt regularly, and is partof a zone of high fire frequency, which occursacross Africa from Senegal to the westernEthiopian escarpment, where it penetrates intothe highlands along the deep river valleys(Jensen & Friis 2001: Fig. 3). This vegetationhas been burning annually for such a long timethat the plants show many adaptations to fire,

BS 55 317

and the vegetation must be assumed not to beadversely affected by controlled annual fires.Such adaptations in the flora of the regionhave been dealt with by Jensen & Friis (2001)and Menassie Gashaw et al. (2002).

The riparian and swamp vegetation consistsof two physiognomically different types, river-ine forests and open almost treeless swamps.Typical trees in the riverine forests are Celtisafricana, Ficus sycomorus, Tamarindus indica Syzy-gium guinense, Kigelia aethiopicum, Lepisanthessenegalensis, Nuxia oppositifolia, Salix mucronata,Trichilia emetica, Diospyros mespiliformis, Mimu-sops kummel, Breonadia salicifolia, Phoenix recli-nata, and species of Acacia and Ficus. There isoften a shrub layer, and lianas and vascular epi-phytes occur. The ground cover includesgrasses ferns, and a few herbaceous dicotyle-dons.

The swamps are dominated by species ofCyperaceae, grasses, and many herbs, of whichmany are not found elsewhere in Ethiopia. Vol-ume 2(1) of the Flora of Ethiopia and Eritrea(Edwards et al. 2000) contains an appendixwith recently recorded species for the Floraarea, and many of these new records haverecently been made in the Benshangul GumuzNational Regional State. The flora of groundorchids in the Benshangul Gumuz NationalRegional State is very diverse for Ethiopia, as isindicated by Cribb et al. (2002).

Exploration of the floraThe flora of the western escarpment ofEthiopia has been rather sporadically explored(Cufodontis 1962; Friis 2001). During his trav-

318 BS 55

Fig. 1. Section of White’s Vegetation map of Africa from1983, showing the total extent of the mapping unit 29b,“Undifferentiated woodlands (Ethiopian type).” The borderbetween Eritrea/Ethiopia (to the right) and the Sudan (tothe left) has been marked with a dotted line. The Ben-shangul Gumuz National Regional State, which is fre-quently referred to in the text, and which covers a largeand topographically very diverse part of White’s mappingunit 29b, is marked with red outline. The eastern part ofthe Gambella National Regional State is marked withgreen outline. The twin towns of Gallabat and Metemmaare marked with a red dot. Reproduced with permission(UPO/D/A/2000-088).

els in the Sudan in 1865-1871 G. Schweinfurthmade a detour into Ethiopia and studied theflora in western Amhara region around Galla-bat and Metemma (Schweinfurth 1865).R.E.G. Pichi-Sermolli explored in 1937 thewestern Ethiopian escarpment in the region tothe west of Lake Tana (Pichi-Sermolli 1951).The lowlands and the western Ethiopianescarpment in the Gambella NarionalRegional State has been studied fairly fre-quently in the years just before and during theEthiopian Flora Project (1980-2004), but mod-ern studies of the flora to the north of theGambella have been rather few. M.G. Gilbert,J.J.F.E. de Wilde, W.J.J.O. de Wilde and B.E. deWilde-Dufjes and M. Thulin visited the westernEthiopian escarpment in the 1960es and1970es, Mesfin Tadesse, Sebsebe Demissew andothers studied the area several times in the1970es and 1980es. I. Friis, Menassie Gashaw, S.Bidgood, Sebsebe Demissew and Tesfaye Awasand others paid visits to the BenshangulGumuz National Regional State the 1990es andin 2000-2001. However, a special contributionto the knowledge of the flora of the Ben-shangul Gumuz National Regional State hasbeen made by C. Hermann, who spent twoyears’ of work for the Ethiopian Department ofAgriculture in Benshangul Gumuz NationalRegional State during 1999-2001. He has par-ticularly enriched our knowledge of the areabecause he has stayed there and collected dur-ing the rainy season.

Together, these studies have indicated thatthe western Ethiopian escarpment hosts aninteresting and partly unique, but as yet poorlyknown flora, as is demonstrated by the exam-ples later in this paper.

Socio-economic conditions, development andpossible threats to the biodiversityAccording to the most recent population cen-sus (Population and Housing Census ofEthiopia 1994), the population of the Ben-

shangul Gumuz National Regional State, acore area in this study, is ca. 460.000 people, ofwhich 92% are settled in rural areas. This givesa density of 10.9 individuals pr km2, while theoverall number for Ethiopia is 57.7. Ten yearsearlier the population was much less dense andthe impact on vegetation accordingly onlyslight. During the famine in Welo and Tigrayaround 1984 100.000 persons were movedfrom the areas in north and north-east and set-tled in the Benshangul Gumuz NationalRegional State (National Atlas of Ethiopia1988). The area used for agricultural produc-tion in the Benshangul Gumuz NationalRegional State amounts to 142.223 ha, onlyabout 2.84% of the region’s area, or 0.36 ha pr.inhabitant (Bureau of Planning and EconomicDevelopment 1998). In many parts of the west-ern Escarpment income is created by collec-tion of gum arabic from Acacia seyal and frank-incense from Boswellia papyrifera. The local tra-dition of gold mining in the western lowlands,especially in the Benshangul Gumuz NationalRegional State, goes back to the AxumiteEmpire, and currently (Bureau of Planningand Economic Development 1998) an averageof 180 kg gold/month is produced in the min-ing season (February to April).

The population on the western escarpmentis growing. The population of the BenshangulGumuz National Regional State is expected tobe double within 2030 (Bureau of Planningand Economic Development 1998), and else-where a similar or slightly lower increase seemslikely.

These changes may present a number ofthreats to the biodiversity.

(1) Loss of wetlands by draining, whichwould mean loss of habitat for the many rareorchids and other wetland species, includingendemics.

(2) Unsustainable development of the wood-lands and bamboo-thickets by uncritical fuel-wood cutting, charcoal-burning and mining,

BS 55 319

which may harm future sustainable exploita-tion of the woody vegetation by the local peo-ple and might threaten some of the woodyendemics.

(3) Unsustainable development of agricul-ture and mining in the wooded grasslands,which might threaten some of the rare grass-land and woodland species.

(4) Change from traditional slash and burnagriculture to large scale cultivation.

It is therefore important that the florabecomes better known so that the threats canbe assessed and proper management plansdrafted and implemented.

Diversity of the western EthiopianescarpmentThe flora of the area covered by this vegeta-tion is not well known, and it is only possibleto present a rough estimate of the diversity.Two of us (Sebsebe Demissew and TesfayeAwas) have compiled a list of 956 species ofvascular plants that are reported to occur inthe Benshangul Gumuz National RegionalState, a core area in the area under study here.The list has been compiled from publishedFlora of Ethiopia and Eritrea accounts andunpublished sources.

It would currently be very difficult to give aprecise count of the species, which occur onthe entire western Ethiopian escarpment, orthe area of White’s Undifferentiated woodlands(Ethiopian type), but a reasonable guess wouldseen to be the number of species in the Ben-shangul Gumuz National Regional State plus10-25%, or a total between 1040 and 1180species. Together, the authors of this paperhave visited many small sectors of the westernEthiopian escarpment, and it is our impressionthat many of the species are widespread in anorth-south direction, even some of thespecies, which are endemic to the escarpment.It is therefore our impression that a list for the

Benshangul Gumuz National Regional Statewill represent a comparatively large proportionof the entire diversity.

Endemism of the western EthiopianescarpmentIn spite of the imperfect knowledge of theflora of the western Ethiopian escarpment,there are a notable number of interesting localendemics or near-endemics which arerestricted to or mainly distributed in White’sUndifferentiated woodlands (Ethiopian type). Thehighest concentration seems to be in the Ben-shangul Gumuz National Regional State, butour knowledge about the distribution of theplant species of the western Ethiopian escarp-ment is still incomplete. The examples we areaware of from our own studies have been sup-plemented by examples found throughsearches through the Flora of Ethiopia andEritrea, but we are sure that many more exam-ples will be found through further studies.These 27 examples are discussed below. We donot know the exact number, but a reasonableguess would probably be to add 10-25%, so thenumber may increase to 30-40.

DicotyledonesAsclepiadaceaeCeropegia recurvata M.G. Gilbert. This a newlydescribed endemic species discovered in theOxytenanthera woodland around Assosa in theBenshangul Gumuz National Regional State ataltitudes between 1300 and 2200 m (Gilbert2002). It is related to Ceropegia melanops H.Huber and C. nigra N.E. Br. from Central andWest Africa. This species occurs in other locali-ties in western Ethiopia, where western taxareach into the Ethiopian highlands in the deepriver valleys; the southernmost example of thisis from the Omo Valley in the Flora of Ethiopiaand Eritrea region GG, a locality which seems to

320 BS 55

be inside the southernmost extension ofWhite’s Undifferentiated woodlands (Ethiopiantype).

AsteraceaeOchrocephala imatongensis (Philipson) Dittrich.This is a species which is fairly widespread inWhite’s Undifferentiated woodlands (Ethiopiantype), but transgresses slightly the borders ofthis area in southern Sudan and northernUganda. It occurs in areas of fierce annualgrass fires in woodlands along the westernescarpment of Ethiopia from Gallabat andMetemma to Gambella, and has outlying local-ities on the Imatong Mountains, both on theSudanese and the Ugandan side. A rather simi-lar distribution is shown by the climber Pepo-nium cienkowskii (Schweinf.) Engl. (Cucur-bitaceae, see below). The relationship of thismonotypic genus is not yet known.

Vernonia cylindrica Sch. Bip. ex Walp. Thisspecies often occurs in undergrowth of Oxy-tenanthera thickets at altitudes between 1200and 1600 m. It seems to be distributed fromwestern part of the Flora of Ethiopia and Eritrearegion TU throughout the bamboo thickets ofBenshangul Gumuz National Regional State. Itis not known elsewhere, and the relationship ofit is not yet known.

Vernonia thulinii Mesfin. This is a fairly recentlydescribed species (Mesfin Tadesse 1997) thatprobably should be included here. It isrestricted to the woodlands of the Didessa Val-ley, but it is well known that species from thewestern Ethiopian escarpment may penetrateinto the highlands along the major river val-leys. The species is not known elsewhere, andthe relationship of it is not yet known.

Vernonia gilbertii Mesfin. This is another fairlyrecently described species (Mesfin Tadesse1997) with a similar, but slightly wider known

distribution than V. thulinii. It occurs in veryopen Combretum-Terminalia-Stereospermum wood-land at 1200-1700 m a.s.l., with a concentrationin the Benshangul Gumuz National RegionalState, but it penetrates further into the high-lands along the big river valleys, and it has itssouthern limit just inside the woodlands ofGambella. It is not known elsewhere, and therelationship of it is not yet known.

Vernonia didessana Mesfin. This is yet anotherfairly recently described species (MesfinTadesse 1997) with a distribution that only justexceeds the Benshangul Gumuz NationalRegional State, where it occurs in woodlandwith Piliostigma, Combretum, Schefflera, Entada,etc., on sandy soil at altitudes between 1220and 1700 m. a.s.l. It is not known elsewhere,and the relationship of it is not yet known.

Laggera braunii Vatke. This species occurs inopen Annona senegalensis woodland and Oxy-tenanthera abyssinica thickets at altitudes be-tween 1300 and 1800 m on the western escarp-ment of the Ethiopian highlands. In spite of itsdistribution in White’s Undifferentiated wood-lands (Ethiopian type) it will have to be classified asa near-endemic, because it is also known fromthe Jebel Marra in western Sudan, but not else-where. The relationship of it is not yet known.

Bidens borianiana (Sch. Bip. ex Schweinf.)Cufod. This species occurs in regularly burn-ing woodlands from ca. 300 to 1200 m a.s.l.from south-western Eritrea along the westernEthiopian escarpment to the northern Ben-shangul Gumuz National Regional State; it alsooccurs in the immediately adjacent parts of theSudan. The relationship of it is not yet known.

CombretaceaeCombretum hartmannianum Schweinf. Thisspecies is a characteristic small tree in thewoodlands along the western border of

BS 55 321

Ethiopia from the extreme south-western partof Eritrea to the Benshangul Gumuz NationalRegional State and the adjacent parts of theSudan at altitudes between 500 and 1200 m.The remarkable drooping and extremely longdrawn-out leaf-tip makes C. hartmannianumeasy to recognise, and the feature is not foundin any other species. It is not known else-where, and the relationship of it is not yetknown.

Combretum rochetianum A. Rich. ex A. Juss. Thisspecies has almost the same distribution area asthe previous one. The relationship of thisspecies is not yet known. It is not known else-where, and the relationship of it is not yetknown.

CucurbitaceaePeponium cienkowskii (Schweinf.) Engl. Thisspecies has been recorded from rocky outcropson the border between the Benshangul GumuzNational Regional State and the adjacent partof the Sudan, but is also known from similarhabitats in the Imatong Mountains, both onthe Sudanese and the Ugandan side, so it isslightly transgressing the limits of White’sUndifferentiated woodlands (Ethiopian type). Arather similar distribution is shown by the tall,shrubby Asteraceae Ochrocephala imatongensis(Philipson) Dittrich. The relationship of thisspecies is not yet known.

EuphorbiaceaePhyllanthus dewildiorum M.G. Gilbert. Thisspecies occurs in woodlands in the deep rivervalleys of the western part of the Flora ofEthiopia and Eritrea regions WG and KF, and itseems to be restricted to the area of White’sUndifferentiated woodlands (Ethiopian type).According to the Flora of Ethiopia and Eritrea, itis closely related to Phyllanthus trichotepalus Bre-nan, known from western Uganda, Rwanda,Burundi and Congo DR.

Euphorbia veneifica Kotschy. This species occursin the Combretum woodlands of the Sudan andwestern Ethiopia, just entering northernUganda, and it does thus transgress the bor-ders of White’s Undifferentiated woodlands(Ethiopian type). The distribution thus resem-bles that of Peponium cienkowskii (Schweinf.)Engl. and Ochrocephala imatongensis (Philipson)Dittrich. The relationship of this species is notyet known.

Fabaceae subfam. PapilionoideaeMucuna melanocarpa Hochst. ex A. Rich. Thisspecies is endemic to Ethiopia and occursmainly on the western escarpment and in thedeep river valleys. It is common in the westernCombretum woodland, but it spreads into suit-able habitats elsewhere in Ethiopia, reachingthe Flora of Ethiopia and Eritrea regions GG andSD, and it may therefore slightly transgress theborders of White’s Undifferentiated woodlands(Ethiopian type). The relationship of this speciesis not yet known.

Rhynchosia stipulosa A. Rich. This species isapparently endemic to the western Ethiopiandeciduous woodlands. It was described fromthe dry woodlands of Shire in Tigray and hasalso been recorded from similar habitats inwestern parts of the Flora of Ethiopia and Eritrearegions WG and GG, which are all withinWhite’s Undifferentiated woodlands (Ethiopiantype). However, in the Flora of Ethiopia andEritrea it is suggested that this species may beconspecific with the widespread Africanspecies Rhynchosia luteola (Hiern) K. Schum.

Vigna frutescens A. Rich. subsp. kotschyi (Schwe-inf.) Verdc. This subspecies is an Ethiopiannear-endemic described from Combretum wood-lands in western Ethiopia and the adjacentparts of the Sudan. It is only known from veryfew collections, which have been collectedinside White’s Undifferentiated woodlands

322 BS 55

(Ethiopian type). However, it may be identicalwith Vigna neumannii Harms, described fromwoodlands in the Ethiopian Rift Valley, but thetype of the later is now lost, and the taxon hasapparently not been recollected. Even if thetwo taxa are united, the resulting taxon wouldbe an endemic or a near-endemic of White’sUndifferentiated woodlands (Ethiopian type).

LamiaceaePycnostachys sp. = Mesfin & Kagnew 2249. Thisapparently undescribed and narrowlyrestricted species has been collected in wet-lands near Assosa, capital of the BenshangulGumuz National Regional State, by Mesfin &Kagnew 2249 and Friis et al. 7919. It would seemto be narrowly restricted inside White’s Undif-ferentiated woodlands (Ethiopian type). It may berelated to P. niamniamensis Gürke from theSudan, Uganda and Kenya.

Scutellaria schweinfurthii Briq. Subsp. schwein-furthii. This subspecies occurs in wooded grass-land subject to regular burning and in rockyplaces with woodland. From Ethiopia it is onlyknown with certainty from the western part ofthe Flora of Ethiopia and Eritrea region WG. It isdoubtfully recorded from the lowlands of IL(Gambella). Outside Ethiopia, it is knownfrom similar habitats in southern Sudan andthe adjacent parts of Uganda, and it doestherefore, like a few other species, slightlytransgress the borders of White’s Undifferenti-ated woodlands (Ethiopian type). The other sub-species, Scutellaria schweinfurthii Briq. subsp.paucifolia (Baker) A.J. Paton, is widespread intropical Africa.

VitaceaeCyphostemma pannosum Vollesen. ThisEthiopian endemic species was described froma specimen collected by Friis et al. (as no. 2409)in Combretum woodland on the westernEthiopian escarpment above Gambella (in the

Flora of Ethiopia and Eritrea region IL), but it hasalso been found from woodlands of the Ben-shangul Gumuz National Regional State and inone similar locality in the Flora of Ethiopia andEritrea region GG, at the south-eastern borderof White’s Undifferentiated woodlands (Ethiopiantype). It is most closely related to the WestAfrican species Cyphostemma flavicans (Bak.)Descoings.

Monocotyledons.In this group, particularly the petaloid mono-cots appear to have speciated in the region.

AmaryllidaceaeCrinum bambusetum Nordal & Sebsebe. This is anewly described species, which is distributednear Assosa in the Benshangul GumuzNational Regional State and in adjacent areasof the Sudan (Nordal & Sebsebe 2002). Alllocalities are inside White’s Undifferentiatedwoodlands (Ethiopian type). It belongs among theCrinum species with star-shaped rather thanbell-shaped flowers, a group with few and rarespecies in Tropical Africa. It is the only Crinumknown to grow in bamboo ticket. The sisterspecies appears to be Crinum subcernuum Baker,distributed disjunctly in southern Africa.

AnthericaceaeChlorophytum herrmanii Nordal & Sebsebe sp.nov. This endemic new species will be formallydescribed below. It is only known from openrocky outcrops in the bamboo forest close toAssosa in the Benshangul Gumuz NationalRegional State. It belongs among the specieswith prostrate inflorescence, but differs fromthe others by its much branched inflorescenceand pubescent leaf undersides. The sisterspecies appears to be Chlorophytum neghellenseCufod., another Ethiopian endemic onlyfound in Bale and Sidamo regions in Acacia-Commiphora woodland and bushland.

BS 55 323

Chlorophytum serpens Sebsebe & Nordal sp. nov.This new species is endemic to Ethiopia andwill be formally described below. It has onlybeen found in open patches in Combretum-Ter-minalia woodland and only in an area north ofAssosa in the Benshangul Gumuz NationalRegional State. Also this species belongsamong the taxa with prostrate inflorescence,and it connects to the widely distributed Chloro-phytum comosum (Thunb.) Jacq. complex, oth-erwise including rainforest taxa. Superficially itresembles the Cameroonian C. petrophilum K.Krause, growing in moss mats in lowland rainforest. The species share the trait of rathershort, broadly lanceolate leaves and very longtrailing inflorescences producing plantlets(pseudovivipary) and very few flowers.

HyacinthaceaeDrimiopsis spicata (Baker) Sebsebe & Stedjecomb. nov. (formalised below). This speciesgrows in grassland at the margin of Combretum-Terminalia woodland and in annually floodedmeadows near river banks. It has beenrecorded from a small area in the Flora ofEthiopia and Eritrea region WG, in the lowlandpart of IL and the adjacent parts of the Sudan.This species is unique in having blue flowers,apparently bridging the morphological gapbetween the genus Ledebouria (with which itshares the flower colour) and the genus Drim-iopsis (with which it shares the reduced bracts,the closed flowers and the sessile ovary). Itmight have originated as an inter-generichybrid, which has overcome sterility and consti-tuted a distinct species. The case is under studyby Sebsebe & Stedje (in prep.).

AloaceaeAloe sp. = Friis et al. 9130. This is an apparentlyundescribed Ethiopian endemic species fromrocky outcrops in the south western part of theBenshangul Gumuz National Regional State. Itwill be described as a new taxon when ade-

quate material has been obtained. It is uniquewithin the genus in having traits making itresistant to fires.

CommelinaceaeCyanotis sp. = Gilbert & Thulin 707. This appar-ently endemic and undescribed species is so faronly known from one collection from rockcrevices the deep river valleys in the westernpart of the Flora of Ethiopia and Eritrea regionWG. The relationship of this species is not yetknown.

CyperaceaeAscolepis eriocauloides (Steud.) Steud. This west-ern Ethiopian endemic occurs in seasonallywet grassland and seepage areas with shallowsoil over rocks, presumably in deciduous wood-land. It was described from the Flora of Ethiopiaand Eritrea region TU and is now also knownfrom western part of the regions WG and KF. Itseems to be restricted to White’s Undifferenti-ated woodlands (Ethiopian type). The relationshipof this species is not yet known.

Discussion and conclusion It seems fairly clear that biogeographically, theflora of the western Ethiopian escarpment(White’s Undifferentiated woodlands (Ethiopiantype)) is linked most closely to the flora of theWest-African Sudanian region (White 1983), ascan be seen from e.g. the distribution of domi-nant tree species such as Anogeissus leiocarpus(see Wickens 1976: Map. 55), and in has mostlybeen included with the Sudanian regional cen-tre of endemism of White (1983).

The western Ethiopian escarpment couldperhaps be considered a transition zonebetween the Afromontane region in Ethiopiaand the Sudanian region in the Sudan. In sev-eral of his phytogeographical maps, White hasindicated the existence of such a transitionzone, e.g. on a map of the Sudanian region

324 BS 55

(White 1983: Fig. 7), but this transition zone isindicated at higher altitudes and above hismapping unit 29b, Undifferentiated woodlands(Ethiopian type). It is as yet too early to draw anyfirm conclusions about the precise phytogeo-graphical position of the western Ethiopianescarpment as a separate phytochorion at somerank. Yet, it is tempting to compare some ofour preliminary observations on diversity andendemism of the area with the results of Friis etal. (in this publication) and see how the areastudied in this paper ranks in comparison withother parts of the Horn of Africa.

Rank in comparison with diversity of otherareas of the Horn of Africa In this paper, it has been established that theentire western Ethiopian escarpment, or thearea of White’s Undifferentiated woodlands(Ethiopian type), has a flora of more than 950species, and perhaps 1040-1180 species.

Compared to the figures found for the vari-ous Flora regions of the Horn of Africa by Friiset al. (in this publication: Fig. 3), such a diver-sity seems to be comparable to a range of Floraregions of the Flora of Ethiopia and Eritrea,where there is both highland and lowland, e.g.EW, TU, GD, GJ and BA. The Flora regions ofFlora of Ethiopia and Eritrea are indicated on amap reproduced in all the published volumes,and in Friis et al. (in this publication: Fig. 2).

We can calculate the expected diversity ofthe western Ethiopian escarpment, based onthe empirical formula found by Friis et al. (inthis publication), where Texp is the number ofexpected taxa in the Flora region and A is thearea in square degrees of the region:

Texp = 587 + 96.57*A

The area of the western Ethiopian escarpmentis, as mentioned in the introduction, approxi-mately 145,000 km2, or, as we consider the lati-tudinal decline in longitude degree insignifi-

cant so close to the equator, 12.0 squaredegrees, for which area the expected diversityaccording to the formula is 1746. Hence, theestimated minus the expected value is between-566 and -706. When compared with Friis et al.(in this publication: Fig. 4), and if our estimateis correct, this will place the diversity of thewestern escarpment at approximately the samerank as the Flora of Ethiopia and Eritrea regionHA and a number of Flora regions in Somalia.However, we must emphasise that so far, this isonly based on very limited evidence.

Rank in comparison with local endemism ofother areas of the Horn of Africa In the list of examples, which we have so farbeen able to put together, there are 27 casesthat can be considered endemics or nearendemics on the western Ethiopian escarp-ment (the area covered by White’s Undifferenti-ated woodlands (Ethiopian type)), and our esti-mate is that future studies may add to this fig-ure, so that the number of endemics mayincrease to 30-40, which – even with conserva-tive estimates – will rank the area analysed hereat a higher position than nearly all theEthiopian and Eritrean Flora regions analysedfor single-region endemics in Friis et al. (in thispublication: Fig. 12), with the exception of HAand SD, but lower than a number of the Floraregions in Somalia.

This means that the endemism (number ofendemics/number of species) of the westernEthiopian escarpment (White’s Undifferentiatedwoodlands (Ethiopian type)) is approximately0.03 (3%). A comparison with Friis et al. (inthis publication: Fig. 13) shows that only thevalues from the Flora of Ethiopia and EritreaFlora regions of HA and SD are comparablewith this, and only among the Flora regions ofnorth-eastern Somalia there are values consis-tently higher than 0.03.

The diversity and endemism of the westernEthiopian escarpment is not likely to be clearly

BS 55 325

reflected in the analyses made in the paper byFriis et al. (2005) as these analyses use the Floraof Ethiopia and Eritrea and the Flora of Somaliaregions as units. The western escarpment andWhite’s Undifferentiated woodlands (Ethiopiantype) cut across nine Flora regions (EW, TU,GD, GJ, WG, IL, KF, GG, SD), which is nearlyone third of the units. Endemism in a compar-atively narrow zone that cuts across so manyunits would tend to blur the results of theanalysis.

Possible reasons for the endemismThe local endemism in White’s Undifferentiatedwoodlands (Ethiopian type) has developed in aregion where the distance between the moun-tains and the dry lowlands is relatively small,and the climatic shift may have been very dra-matic in relation to Pleistocene fluctuationsbetween wetter and drier periods (cf. White1993). The flora of such areas would beexpected to have suffered from severe extinc-tion, but it has been shown that elsewhere suchareas in fact can be rich in species and particu-larly in endemicity, as is e.g. shown by the dis-cussion of the transitional zone between theAfromontane and the Somalia-Masai region in’the Flora of Ethiopia and Eritrea regions BA andSD by Sebsebe Demissew et al. (2001, p. 245),and of the transition zone with Juniperus-Buxus-Acokanthera between the Afromontane regionand the Somalia-Masai region by Friis (1992).

The mechanisms that support the evolutionof an endemic flora in such places are as yetundocumented, but a possible explanation ofthe endemics and near endemics in White’sUndifferentiated woodlands (Ethiopian type) mightbe the complex topography and the relativelyreliable oreographic rain on the westernEthiopian escarpment, which, with the deephinterland of deep river valleys, would seem toprovide small refugia during time of adverseclimatic conditions. This may have securedniches of very restricted range where species

could survive unfavourable periods. The bestconditions for such niches are likely to havebeen in the most topographically and geologi-cally complex area in the lower reach and atthe mouth of the biggest river system in west-ern Ethiopia, the gorges of the Abay river andits tributaries, an area that approximatelyagrees with the extension of the BenshangulGumuz National Regional State, the areaapparently most rich in local endemics.

Two new endemic species ofChlorophytum (Anthericaceae) and anew combination for an endemicspecies of Drimiopsis (Hyacinthaceae)Chlorophytum herrmannii Nordal & Sebsebe, sp.nov.

Type: Benshangul Gumuz National RegionalState, Anbessa Chaka, ca. 24 km SE of Assosa,9º 54’ 41” N 34º 39’ 35” E, 1590 m, 27.05.2001,Herrmann 220 (ETH holotype, K isotype, Fig.2A).

Haec species nova habitu prostrato foliorum etinflorescentiarum C. neghellensi Cufod. similis, seddiffert radicibus carnosis (non tenuibus tubera later-alia habentibus), foliis nec secus marginem et innervis; inflorescentia valde ramosa, pedicello articu-lato, non curvato. Inflorescentia prostrata ut in C.humifuso, sed foliis brevioribus, prostratis (non erec-tis), rosulatis, (non distichis), ciliatis (non glabris) etinflorescentia ramosa differt.

Perennial herbs with short horizontal rhi-zomes carrying fleshy roots. Leaves rosulate,slightly petiolate, lanceolate, up to 20 x 3.5 cm,acute with hyaline, crispy undulate margin, cil-iate on margin and the veins abaxially. Pedun-cles 2-2.5 cm long, prostrate with short hairs.Inflorescence a much branched panicle, 4-12cm long, also flat on the ground. Bracts largeand leaf-like, up to 20 x 5 mm, ciliate alongmargin and veins. Pedicels straight, 2-4 at eachnode, 5-6 mm long at anthesis, articulated inthe lower half. Flowers white with brownish

326 BS 55

BS 55 327

Fig. 2. (A). The new species Chlorophytum herrmannii Nordal & Sebsebe, based on the holotype from Benshangul GumuzNational Regional State (Herrmann 220). (B). For comparison, Chlorophytum neghellense Cufod., based on plant fromSidamo in southern Ethiopia (Nordal 2218).

tips, tepals 5-6 x 2 mm with 3-5 veins. Stamensshorter than the tepals, filaments 3-4 mm long,anthers 2 mm. Styles straight. Fruits and seedsnot known.

The species epithet honours the collector,Christof Herrmann, who, during his work forthe Benshangul Gumuz National RegionalState, extended the knowledge of the region’sbiodiversity considerably.

The species grows on open rocky outcrops inbamboo forest, around 1600 m. It is onlyknown from the Assosa area in the BenshangulGumuz National Regional State (Flora of

Ethiopia and Eritrea region WG). The main flow-ering period is in June.

Based on morphology, C. herrmannii mightwell be the sister species of another fairly nar-row Ethiopian endemic, C. neghellense (Fig.2B), growing in Acacia-Combretum-Commiphoradominated woodland, often heavily grazed, onred sandy soils between 1000 and 1700 m, inFlora of Ethiopia and Eritrea regions SD and BA.

Chlorophytum serpens Sebsebe & Nordal, sp. nov. Type: Benshangul Gumuz National Regional

State, 71 km from Chagni towards Guba

328 BS 55

Fig 3. A-B. The new species Chlorophytum serpens Sebsebe & Nordal, based on the holotype from Benshangul-GumuzNational Regional State (Sebsebe Demissew et al. 6080). Drawn by Svetlana Voronkova. A. complete plant. B. Detail of flower.C. For comparison, Chlorophytum petrophilum Krause, based on the holotype from Cameroon (Zenker 4846).

(Mankush), 11º 12’ N 36º 07’ E, 1100 m,23.07.2001, Sebsebe Demissew, Tesfaye Awas,Melaku Wandafrash & Kagnew H. Sillasie 6080(ETH holotype, K isotype, Fig. 3A, B).

Haec species nova C. petrophilo Krause similis,brevissima folia et longissimas inflorescentiashabens, praecipue viviparia multiplicans, differtradicibus brevibus, in tuber distinctum terminan-tibus, rosula foliorum sine internodiis, foliis distincteciliatis et firmis non membranaceis.

Perennial herbs with short rhizomes carry-ing short roots ending in distinct tubers.Leaves rosulate, petiolate, broadly lanceolate,7-10 x 2-3 cm, with ciliate margins. Peduncleslax arcuate to trailing, glabrous. Inflorescenceup to 50 cm long, simple or with one branch.Bracts 5 – 15 mm, acute to acuminate. Pedicels,single or paired at the nodes, 4-8 mm long atanthesis, articulated near or below the middle.Flowers white, tepals patent, 3-5 x 1.5-2 mmwith 3-veins. Stamens shorter than the tepals,filaments 2-3 mm long, anthers ca. 1.5 mm.Styles straight. Fruits and seeds not known.

The species name refers to the trailing, thusserpent-like habit, of the inflorescence.

The species grows in Combretum-Terminaliawoodland with tall Sorghum and Pennisetumspecies, around 1100 m. It is only known fromthe type locality in the Flora of Ethiopia andEritrea region GJ. It flowers in July.

Both C. serpens and C. petrophilum belong in thewidespread, heterogeneous C. comosum(Thunb.) Jacq. complex, a complex wherepseudovivipary is common. C. petrophilum is arainforest taxon, only found in the wettestcoastal forests of Cameroon. The particular traitsof the relatively short broadly lanceolate leavesand the very long trailing inflorescences mighthave evolved independently in the two species.

Drimiopsis spicata (Baker) Sebsebe & Stedje,comb. nov.

Basionym: Scilla spicata Baker in Journ. Bot.1878: 323 (1878).

Types: The Sudan, Jur, east of the river Wau,Schweinfurth 1641 (K syntype); by the RiverWau, Schweinfurth 1652 (K syntype)

[next person in K should lectotypify] Synonym: Drimiopsis barteri sensu Stedje, non

Baker, in Flora of Ethiopia and Eritrea 6: 139 (1997).The species is referred to the genus Drimiop-

sis due to its reduced bracts, the closed flowerand the sessile ovary. It is, however, easilyrecognised from other species in the genus byits purplish to bluish flowers, all others havewhitish to greenish. The particular flowercolour reminds of traits found in the closelyrelated genus, Ledebouria.

The species grows in grassland at the marginof Combretum-Terminalia woodland, in annuallyflooded meadows near river banks. It isrecorded from the Flora of Ethiopia and Eritrearegions WG and IL and from adjacent parts ofthe Sudan. The flowering period is from Aprilto May.

AcknowledgementsWe wish to thank Dr. P.H. Wagner, BotanicalLibrary, University of Copenhagen, for trans-lating the diagnoses in the Appendix intoLatin. Two of us (Sebsebe Demissew and IngerNordal) would like to acknowledge Financialsupport from NUFU to work on the Biodiver-sity of Eastern Africa (Lilies, Orchids andSedges) – Taxonomy, Conservation and Use.

Literature cited

Bureau of Planning and Economic Development. 1998.Population Projection for Benishangul Gumuz NationalRegional State 1994-2003. Unpublished.

Cribb, P., Herrmann, C., & Sebsebe Demissew. 2002. Newrecords of orchids from Ethiopia. Lindleyana 17: 178-188.

Cufodontis, G. 1962. The botanical exploration of North-east Tropical Africa. In: Fernandes, A. (ed.), Comptes Ren-dus de la IVe Réunion plénière de l’Association pour l’Étudetaxonomique de la Flore d’Afrique tropicale. Lisbonne et Coïm-bre, 16-23 septembre, 1960. Lisboa. Pp. 233-248.

BS 55 329

Edwards, S., Mesfin Tadesse & Hedberg, I. (eds.), 1995.Flora of Ethiopia and Eritrea. Vol. 2,2. Canellaceae to Euphor-biaceae. Addis Ababa, Ethiopia & Uppsala, Sweden.

Edwards, S., Mesfin Tadesse, Sebsebe Demissew & Hed-berg, I. (eds.), 2000. Flora of Ethiopia and Eritrea. Vol. 2,1.Magnoliaceae to Flacourtiaceae. Addis Ababa, Ethiopia &Uppsala, Sweden.

Edwards, S., Sebsebe Demissew & Hedberg, I. (eds.), 1997.Flora of Ethiopia and Eritrea Vol. 6. Hydrocharitaceae to Are-caceae. Addis Ababa, Ethiopia & Uppsala, Sweden.

Feasibility Study. 2001. Feasibility Study and EnvironmentalImpact Assessment for: Assosa-Guba Road project. NDF CreditNo. 207-TD1. November 2001. Carl Bro a/s TransportDepartment, in association with DANA Consult Plc Engi-neering Consultants.

Friis, I. 1992. Forest and Forest Trees of Northeast TropicalAfrica. Their Natural Habitats and Distribution Patternsin Ethiopia, Djibouti and Somalia. Kew Bull., Addit. Ser.15.

Friis, I. 2001. Progress with the botanical exploration ofEthiopia and Eritrea during the last forty years. Systemat-ics and Geography of Plants 71: 165-186.

Friis, I. & Sebsebe Demissew. 2001. Vegetation maps ofEthiopia and Eritrea. A review of the existing maps andthe need for a new map for the Flora of Ethiopia andEritrea. Biol. Skr. 54: 399-439.

Friis, I., Thulin, M., Adsersen, H. & Bürger, A.-M. 2005. Pat-terns of plant diversity and endemism in the Horn ofAfrica. Biol. Skr. 55: 289-314.

Gilbert, M.G. 2002. Notes on the Ceropegiae (Asclepi-adaceae) of Ethiopia. Nord. J. Bot. 22: 205-210.

Hedberg, I. & Edwards, S. (eds.), 1989. Flora of Ethiopia. Vol.3. Pittosporaceae to Araliaceae. Addis Ababa and Asmara,Ethiopia & Uppsala, Sweden.

Hedberg, I. & Edwards, S. (eds.), 1995. Flora of Ethiopia andEritrea. Vol. 7. Poaceae. By Sylvia Phillips. Addis Ababa,Ethiopia & Uppsala, Sweden.

Jensen, M. & Friis, I. 2001. Fire regimes, floristics, diversity,

life forms and biomass in wooded grassland, woodlandand dry forest at Gambella, western Ethiopia. Biol. Skr.54: 349-387.

Menassie Gashaw, Michelsen, A., Friis, I., Jensen, M., Seb-sebe Demissew & Zerihun Woldu. 2002. Post-fire regen-eration strategies and tree bark resistance to heating infrequently burning tropical savanna woodlands andgrasslands in Ethiopia. Nord. J. Bot. 22: 19-33.

Mesfin Tadesse. 1997. New species of Vernonia (Composi-tae-Vernonieae) from northeast Africa. Kew Bull. 52: 575-592.

National Atlas of Ethiopia. 1988. National Atlas of Ethiopia.1. edition. Ethiopian Mapping Authority, Addis Ababa.

Nordal, I. & Sebsebe Demissew. 2002. Crinum bambuse-tum, a new species of Amaryllidaceae from North EastAfrica. Kew Bull. 57: 465-469.

Pichi-Sermolli, R.E.G. 1951. Missione di Studio al Lago Tana.Vol. 7. Richerche Botaniche. Parte I. Fanerogame raccolte nelBacino Idrografico del Lago Tana, nel Semién, nella Regione diTucùr-Dinghià ed in Eritrea. Academia nazionale dei Lin-cei, Roma.

Population and Housing Census of Ethiopia. 1994. Resultsfor Benshangul Gumz R.S. Vol. I, Statistical Report & Vol. II,Analytical Report. Addis Ababa.

Schweinfurth, G. 1865. Vier Briefe an Dr. H. Barth. Z. Allg.Erdk. 19: 305-324, 385-427.

Sebsebe Demissew, Nordal, I. & Stabbetorp, O.E. 2001. Pat-terns of endemism of the genus Aloe in the Flora ofEthiopia and Eritrea. Biol. Skr. 54: 233-246.

White, F. 1983. The vegetation of Africa: A descriptive memoir toaccompany the UNESCO/AETFAT/UNSO vegetation map ofAfrica. UNESCO, Paris.

White, F. 1993. Refuge theory, ice-age aridity and the his-tory of tropical biotas: an essay in plant geography.Fragm. Florist. Geobot. Suppl. 2(2): 385-409.

Wickens, G.E. 1976. The Flora of Jebel Marra (SudanRepublic) and its geographical affinities. Kew Bull.,Addit. Ser. 5.

330 BS 55