This article was downloaded by: [University of Auckland Library]On: 17 December 2014, At: 14:08Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Giornale botanico italiano: OfficialJournal of the Societa Botanica ItalianaPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/tplb19

The succulent flora of South Africa andNamibia: representation and distributionErnst Van Jaarsveld a & Mike Struck aa Kirstenbosch National Botanical Gardens , Private Bag X7,Claremont, 7735, South Africab Botany Department , University of Cape Town , Private Bag,Rondebosch, 7700, South AfricaPublished online: 14 Sep 2009.

To cite this article: Ernst Van Jaarsveld & Mike Struck (1995) The succulent flora of South Africa andNamibia: representation and distribution, Giornale botanico italiano: Official Journal of the SocietaBotanica Italiana, 129:1, 439-450, DOI: 10.1080/11263509509436161

To link to this article: http://dx.doi.org/10.1080/11263509509436161

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

T h e succulent f lora of Sou th Afr ica a n d Namibia: representa t ion a n d d i s t r i b u t i o n

ERNST VAN JAARSVELD" and MIKE STRUCK**

* Kirstctibosch h'ational Botanical Cardctis, Private Bag X7, Claretnotit, 7735, Sorrtli Africa. **Botany Dcparttucnt, University of Cape Towti, Private Bag, Rotidcboscli, 7700, Sorcth Africa.

ABSTRACT. - Taxonomic rcprcscntation and regional distribution pattcrns of taxa, lifc forms, and dcfcncc mcchanisms of thc succulent flora of South Africa and Namibia arc quantified and discusscd in rclation to physical and biotic factors. Habitats arc invcstigatcd and for cach rcgion ccntrcs of succulcnt spccics richness arc pointcd out.

Key words: Succulcnt, Southcrn Africa. Distribution.

INTRODUCTION

South Africa and Naniibia arc ycll known for thcir rich plant divcrsity (21 137 spccics gL 13 cndcniic faniilics) of which tlic succulcnt flora fornis an important part (ARNOLD Br

JAARSVELD, 1987). Thc succulcnt flora divcrsity is probably thc richcst in thc world with high lcvcls of cndcniisni (VAN JAARSVELD, 1987, SMITH ct a!.. 1993). Thc high succulcnt proportion is a rcflcction of thc harsh arid to scmi-arid cliniatic conditions ovcr two thirds of tlic subcontincnt. Succulcnt plants arc rcprcscntcd in all phytogcographic regions of southcrn Africa up to thc highcst mountain pcaks. Tlicir divcrsity incrcascs grcatly to tlic wcst and south whcrc thcy bcconic tlic dominant lifc forni in tlic scnii-arid wintcr rainfall rcgion ("Southcrn African Leaf Succulcnt Zonc", Jiirgctis 1986). Lifc fornis vary from annuals, likc thc Livingstonc daisy (Dorothcnritliirs bcllidiforrriis) and niiniaturc caudicifornis, such as Aiiocnni/mr.os bojcriorm. to hugc succulcnt trccs likc thc baobab (Ahtisotiin digitotn). Tlic aini of thc prcscnt contribution is to providc a synopsis of thc succulcnt flora of southcrn Africa (South Africa, Namibia, Lcsotho, Swaziland) with spccial cnipliasis on distribution and vcgctativc adaptions. Aftcr a bricf introduction into tlic physical and climatic fcaturcs of thc southcrn African subrcgion, pattcrns of distribution and divcrsity of succulcnt plants within thc niajor vcgctation regions arc rcvicwcd. Thc taxononiic rcprcscntation as wcll as thc rcprcscntation of succulcnt lifc and growth fornis and dcfcnsc mcchanisms is quantified and discussed in vicw of thc southcrn African succulcnt flora as a wliolc and in rclation to physical and biotic factors of tlicir habitats.

DE WET. 1993, CO\VLING 6r HILTON-TAYLOR, 1994. SMITH C t aI., 1993, VAN

METHODS

Tlic idcntification of "typical" succulcnt plants is fairly straightfonvard. Ncvcrthclcss, thc distinction bctwccn succulciicc and non-succulcncc or othcr fornis of storagc rcniains ambiguous,particularly in tlic caudicifomis and gcophytcs. In thc prcscnt account thc definition of VON WILLERT c f nl. (1992) is adopted which rccognizcs a succulcnt as ''a plant posscssing at lcast onc succulcnt tissuc. A succulcnt tissuc is a living tissuc that, bcsidcs possiblc othcr tasks, scrvcs and guarantccs an at lcast tcniporary storagc of utilizablc watcr, which niakcs thc plant tcniporarily indcpcndcnt of an cxtcrnal water supply whcn soil watcr conditions h a w so dctcrioratcd that thc root is no longcr ablc to providc thc ncccssary watcr from soil." Howcvcr, in thc prcscnt analysis Cycads. cpiphytic orchids and most gcopliytcs wcrc cxcludcd cxccpt tliosc with cpitcrrancan, more

GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129. I . 1995 439

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

or lcss succulcnt bulbs (c.g. Uriiifhogahrrz longibracrcarurrt) and thosc with additional succulcnt parts (c.g. Laclienulia pafirla). Spccics nunibcrs wcrc conipilcd from ARNOLD & DE WET (1993) and HARTMANN (1991, for Mcscnibryanthcniaccac) as wcll as thc latcst rcvisions of succulcnt tam. Thc spccics wcrc thcn catcgorizcd according to taxonomic rcprcscntation, life forms and dcfcnsc stratcgics. All catcgorics wcrc firstly vicwcd for tlic southcrn African succulcnt flora as a wholc and sccondly for cach major vcgctation region. Duc to tlic many transgrcssions bctwccn succulcncy and non- succulcncy sonic dcgrcc of subjcctivity is incvitablc. Thcrc is also a "grcy zonc" towards halophytcs (c.g. Psi/ocaii/ori dinmi). Morcovcr, in scvcral groups thc nunibcr of spccics is controvcrsial and thus a qucstion of how narrow or widc a spccics conccpt has bccn adoptcd in tlic latcst rcvision. Scvcral largcr gcncra, c.g. of tlic Mcscmbryanthcniaccac and Euphorbiaceac, havc not bccn rcviscd sincc thcir inccption in thc beginning of this ccntury and arc possibly biascd by outdatcd taxononiic conccpts. Rcgarding distribution data, soutlicrn Africa is largcly undcrcollcctcd and tlicrc arc a nunibcr of dcgrcc squarcs in thc Nania-Karoo without a singlc plant record in any of thc South African hcrbaria (Gll%BS RUSSELL cf 01.. 1984)! For thcsc regions prcscnt distributidn pattcrns nicrcly rcflcct tlic statc (or ratlicr lack) of ficld work. Howcvcr, due to thc scnior author's 20 ycars of cxpcricncc with succulcnts in tlic ficld and undcr cultivation, tlic prcscnt analysis niay bc considcrcd as rcprcscntativc.

THE STUDY AREA

TOPOGRAPHY

In siniplc tcniis southcrn Africa can bc dcscribcd as an cxtcnsivc platcau of about 1000 111 nican altitudc which is surroundcd by a 50 to 150 kni widc plain along tlic coast linc. Thc dcclincs, tcrniinating, in thc Snccubcrg and Nuwcvcld mountains in thc south and thc Klianiicsbcrg and Roggcvcld Mountains in thc wcst. In Namibia tlic cscarpnicnt mountains arc known as tlic Huib Platcau and Hunsbcrgc in tlic south and tlic Khonias Hochland in central Naniibia. Tlic northcr ccntrril part of tlic platcaii is fairly cvcn and consists of a sandy plain known as tlic Kalaliari. Thc Capc Foldcd Mountains. a proiiiincnt fcaturc of thc south and south wcstcrn Cnpc. arc situatcd bctwccn tlic southcrn margin of tlic cscarpnicnt mountains and tlic sca. Thcsc mountain rangcs arc niorc or lcss parallcl to thc south coast with an avcragc higlit of ovcr 1.000 ni a.s.1. Parts of thc Capc Foldcd Mountains causc rain shadows for thc low lying arid intcrniontnnc basins of thc Kiiroo; the Littlc Karoo is situatcd bctwccn the Groot Swartbcrg ilnd Langcbcrg niountain nngcs, tlic Ccrcs Karoo Iccwards of tlic Ccdcrbcrg and Koucbokkc\icldbcrgc.

CLI.\lATE

Thc cliniatc of southcrn Africa is dctcrniincd by thc prcvailing subtropical high prcssurc systciiis in thc north and tlic circunipolar cycloncs in tlic south, as wcll as its position bctwccn tlic cold Bcngucla current in tlic wst i d thc wariii Mozanibiqucan Clianncl in tlic cast. Thus. tlic nortlicrn part of thc subcontincnt strctchcs \wll into thc subtropics, whcrcas thc southcrn part lics in tlic rcalni of a warm tcnipcratc zonc. Bcsidcs, tcnipcraturc rcginics arc greatly niouldcd by thc gcogmpliic and orographic situation of a locality. Thc following cxaniplcs niay dcnionstratc tlic point: Tlic sniall diffcrcncc in nican annual tcmpcraturc bctwccn Capc Town ( 1 7 "C) and Prctoria ( I 7.5 "C) is duc to thc high clcvation of thc lattcr locality (abovc 1000 m a.s.1.). Tlic 7°C diffcrcncc bctwccn tlic avcragc tcnipcraturcs at Port Nollotli and Durban (both bctwccn 20" and 30" soutlicrn latitudc) is a dircct rcsiilt of tlic watcr tcnipcraturcs of thc Atlantic and Indian Occans, rcspcctivcly. Thc highcst avcragc tcnipcraturcs in South Africa wcrc rccordcd froni Koniaticpoort at thc Mozanibiqucan bordcr (23.3 "C, 25'30' southcrn latitudc) and Goodhousc (23.3 "C, 29" southcm latitudc) situatcd in thc cxtrcmcly dry

440 GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129, I , 199.5

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

vallcy of tlic lowcr Orange Rivcr sonic 150 km cast of thc Atlantic coast. Most of southcrn Africa, including thc northern and northeastern parts of South Africa and Namibia, rcccivc sunimcr rainfalls (mainly thunder sliowcrs) which dccrcasc fairly stcadily from cast to wcst. In contrast, tlic southwcstcrn and cxtrcnic wcstcrn parts rcccivc cyclonic rains from thc south during wintcr. As a rcsult two thirds of thc south African and Namibian area is scmi-arid to arid with avcragc rainfall bclow 450 mni. Over most of southcrn Africa thc dry conditions arc duc to thc prcvailing high prcssurc systcnis ncar 30" south. The cold Bcngucla current causes further-aridity along tlic wcstcrn margin o f . South Africa and Namibia and causes tlic forniation of regular fog so typical for tlic Naniib and adjaccnt coastal regions. Mountain rangcs causing rain shadows ,in thc south and south wcst rcsult in arid conditions in thc low lying basins of thc Ccrcs and Little KiXOO.

VEGETATION AND PHYTOGEOGRAPHIC SUBDIVISION

Various attcnipts liavc bccn niadc to classify thc vcgctation and to asscss phytogcographic, structural or bionic boundarics within thc prcscnt study area (c.g. ACOCKS. 1953, GIIIBS-RUSSELL, 1987, HILTONTAYLOR, 1987, JURGENS, 1986. 199 I , RUTHERFORD 6r WESTFALL. 1986, \VERGER, 1978A.II. WHITE, 1983). For thc prcscnt account thc bionic classification of RUTHERFORD & WESTFALL (1986) is adopted as a basis, howcvcr, with anumbcr of anicndnicnts in accordancc with tlic latcst litcraturc (scc bclow). T ic dclirnitation of tlie originally six bionics was bascd on thc coniposition of thc life fornis prcdominant in tlic vcgctation. For thc prcscnt purposc four broad catcgorics arc dcliniitcd. nanicly.

- tlic warm tcmpcratc hcatli and scnii-arid to arid shrublands of thc wintcr rainfall rcgion (Grcatcr Capcnsis),

- the opcn arid shrublands of the interior rccciving mainly suninicr rainfall (Nania- Karoo).

- thc mainly subtropical siimrncr rainfall flora of tlic north and cast (Savanna), and - the high altitudc, moist grassland of tlic Drakcnsbcrgc and adjaccnt parts (Afro-

tcnipcntc grassland and forests). As will bc discusscd bclow, thc anicndnicnts from tlic original bionic milp of

RUTHERFORD & WESTFALL (1986) wcrc dcrivcd from niorc rcccnt phytogcographical approaclics. For convcnicncc. thcsc units will bc tcrnicd "rcgion". without formal iniplication.

GREATER CAPENSIS

Thc Capcnsis or Capc Floristic Rcgion, situated in tlic soutli\vcstcrn corncr of South Africa, is rcnown for its liigli plant cndcniisni (68% spccics, 19.58 gcncra, G filniilics) and thc higlicst spccics tlcnsity of any cquivalcnt-sized tcnipcriitc or tropical rcgion in tlic world (BOND & GOLDIILATT. 1084. COWLING & HOLMES, 1902). Duc to its outstanding floristic richncss this rcgion has bccn rccognizcd ;is a floral kingdom of its own (TAKHTAJAN, 1986). Floristic affinities and circuniscriptions of tlic Capc Floristic Rcgion wcrc rcpciltcdly dcbatcd. Various authors (c.g. BAYER. 1984, JURGENS, 1991) now rccognizc tlic Cape Floristic Rcgion and tlic Succulcnt Karoo Rcgion (scc bclow) as integral parts of tlic "Grcatcr Capcnsis". a conccpt which is adoptcd hcrc. With an approxiniatc area of 150,000 kniy ( I 1 % of tlic south African and Namibian arca) tlic Grcatcr Capcnsis is ccologically. structurally, and floristically highly divcrsc. Thc vcgctation of tlic liigli rainfall arcas in thc south and soutliwcst is known by tlic vcrnacular nanic "fynbos" (fine[-lcavcdj bush). Fynbos consists of tlircc basic forms, tlic distribution of which is largely dctcrniincd by soil paranictcrs (scc COWLING f;: HOLhlES. I992 for dctails): l l ic hcatli-like typical fynbos occurs on dystrophic quanzitic

GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129. I . 1995 441

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

sandstonc mountain chains of thc southwcstcrn and southern Cape; rcnostcr shrubland (rcnostcrbos = Elyrropappirs rlritroceroris) occurs on shalc or granitc soils and Strandvcld vcgctation on sandy alkalinc soils closc to thc coast. Annual rainfall in tlic fynbos rcgions is bctwccn 600 and 2000 nim. Rccurrcnt fires havc bccn an important fcaturc of thc fynbos and thc vcgctation is doniinatcd by plants with life stratcgics adapted to the firc rcgimc ("rcsccdcrs" and "rcsproutcrs"). Many short livcd rcsccding lcaf succulcnts as tvcll as a fcw rcsprouting succulcnt spccics form part of thc fynbos (VAN JAARSVELD Br COWLING, 1994). Thcscincludc a nunibcr of Mcscnibryanthc~iiaccac ("mcscmbs") of c.g. thc gcncra Ruschia, Lampranthus, Carpobrotus and Clcrctum as wcll as Crossrrlo spp., thc gcophytic Errphorbia firberoso and a fcw cndcniic alocs such as Aloe plicofilis (furnishcd with a corky bark), A. haenratifhifolio, A. sirccofritio (thc lattcr two in rocky placcs) and thc rcsprouting A. coniixto. Transitions bctwccn fynbos and Succulcnt Karoo vcgctation arc largcly associatcd with increasing aridity and soil paranictcrs (e.g. COWLING Br HOLMES, 1992). Tlic Succulcnt Karoo Rcgion (scnsu Jiirgcns 1991) cnconipasscs tlic arid parts of thc wintcr rainfall region and adjaccnt "nicridional" units (+ 50-300 nini nican annual rainfall). This region is clcarly doniinatcd by leaf succulcnt chamacpliytcs of tlic Mcscnibryantlicniaccac in particular; othcr proiiiincnt succulcnt faniilics arc thc Asclcpiadaccac, Astcraccac (Ofhotitia, Sctiecio). Crassulaccac and Portulacaccac. Thc Succulcnt Karoo has also a rich annual (niost promincntly Astcraccac) and gcopliytic flora which is world famous for its stunning displays of spring flowcrs. Soils arc dcrivcd from alluvial plains, Enon conglonicratc, shalc niudstonc. sandstonc. granitc and quartzitic outcrops. This region is uniquc in that it has bccn rccognizcd both as a forniation of zonal iniportancc (due to tlic prcdominancc of leaf succulcnts) and a phytochorion of its own (based on the floristic distinctncss) (JURGENS, 1986, 1990, 1991). Succulcnt Karoo vcgctation occurs in thc fcrtilc, dry intcrniontanc basins in tlic south (Little Karoo and Ccrcs Karoo), in Naniaqualand along tlic wcst coast and thc cscarpnicnt mountains into southcrn Namibia and furthcniiorc in a slcndcr but cxtcndcd strip along tlic coast up to about 20' southcrn latitudc (JURGENS, 1991).

N A h l h - K A R W

Thc dcliniitation of tlic Nania-Karoo follows thc phytogcographic subdivision by JmGENS (1991). His Nania-Karoo Rcgion covcrs Daniaraland and Kaokoland, tlic inland parts of thc Niimib outsidc the Succulcnt Karoo cxtcnsion (scc above), tlic Nanialand and Huib platcaus and tlic south African ccntnl platcau (Buslinianland and Uppcr Karoo). On the bionic Icvcl. niost of tlic Dcscrt and thc Nania-Karoo Bionic (scnsu RUTHERFORD 6r WESTFALL, 1986) arc tlius anialgamatcd. In this cixuniscription, thc Nama-Karoo covcrs about 610. 000 kni2 which is tlic second largcst surfacc arca of all thc pliytogcographic rcgions involvcd. It has a fairly rich succulcnt flora which is, howcvcr, poor in comparison to tlic Succulcnt Karoo and tlic scnii-arid subtropical parts. Ncvcrthclcss. a ccntrc of divcrsity and cndcmisni for Mcscnibryantlicniaccac (HARTMANN, 1991, JURGENS. 1986, 1991) and othcr succulcnts (c.g. Atiocnnrpseros, GERBAULET, 1992a.b) is situated in thc vicinity of Wamibad (Namibia) and Pofaddcr (South Africa) ("Pofaddcr Ccntrc", scc bclow). In contrast, thc northcrn part of thc Nama-Karoo and thc hot and dry Orangc rivcr vallcy providc habitats for largcr subtropical savanna clcnicnts, of genera likc Corruriiplrorn. Cerorio, Cyplrosteninrtr, Eiipliorbin, Pocliypodiiirii. In addition, many dwarf and camouflaged cryptic mimics of Lithops and othcr gcncra occur. Annual rainfall of the nortlicrn part of thc Nania-Karoo is bclow 100 nini andwintcr tcnipcraturcs arc mild. Tlic southcrn part of thc Nama-Karoo consists of an opcn shrubland with xcroniorphic, dwarf chamacpliytcs of thc Astcraccac. Scrophulariaccac, Polygalaccac, Bignoniaccac (Rhi.qozirirr) and a fcw grass spccics. Annual rainfall is about 125-250 nini, and wintcr rain is occasionally rcccivcd along tlic wcstcrn border. In largc parts hcavy frost is a coninion phcnomcnon during wintcr. Of thc succulcnt spccics, the

412 GIORNALE BOTANIC0 ITALIAN0 - VOLUME 129, I , I995

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

Mcscmbryanthcniaccac arc also wcll rcprcscntcd here, although thc ccntrc of thc south African platcau features a remarkably low spccics frcqucncy (HARTMANN, 1991; JURGENS, 1986). On tlic othcr hand, spiny nicscnibs pcnetratc dccply into the central platcau; in certain arcas, some spccics are proniincnt. if dominant, clcmcnts of ovcrgrazcd and dcgndcd rangelands (HARTMANN & SmBER, 1993).

SAVANNA

Thc Savanna region - with sonic 752,000 km2 thc largest of thc regions involvcd - can bc subdivided into an arid and a moist part. Arid Savanna ("bushvcld") consists of grassland and flat-topped Acacia, Combrctum and Ficus trccs so typical of Africa. I t strctchcs from nortlicrn Namibia to thc Kalahari (Botswana) and further to the low altitudc regions of thc Northcrn Provincc and Eastern Transvaal (South Africa). Duc to tlic niorc divcrsc topography, niultiplc transgrcssions occur bctwccn arid and nioist Savanna in tlic castcrn Transvaal, along tlic low lying areas of Natal. and tlic castcrn part of thc Eastern Capc. In this region, arid savanna is confined to thc rivcr vallcys and thc intcrniontanc basins. Annual rainfall ranges from 250-500 nini and occurs mainly bctwccn Octobcr and May. Gcncrally. arid savanna is coniparably poor in succulcnts: A chccklist of the Kalahari Gcnisbok Park conipriscs but 33 succulcnt plant spccics (VAN ROOYEN el. 01.. 1988). coniparcd to 134 spp. rccordcd froni thc wliolc of Botswana (HARGREAVES, 1990). Thc succulcnt flora consist niainly of tall shrubby or arborcsccnt stcni succulcnt of gcncra like Eirpliorbio, Arleniirrri, Adenia, or Pncliypotlirrm and firni, sniall to tall, hard-lcafcd Aloe spccics. In tlic nortlicrn Transvaal and nortlicrn Namibia thc baobab (Arlorisoriio rligitolo) is proniincnt. In contrast, tlic nioist parts of tlic Savanna region of Natal and castcrn Transvaal and thc castcrn Cape (all South Africa) carry a rich succulcnt flora. Local cliccklists comprisc I37 succulcnt spccics for tlic Krugcr National Park (VAN DER SCHIJFF, 1969), 192 for.Swaziland (COMPTON, 1976) and 353 for Natal (ROSS, 1972). Annual rainfall is considcrably highcr (500-I000 nini pcr annuni). A typical fcaturc of tlicsc arcas is tlic high proportion of spincsccnt, succulcnt and nonsucculcnt plants. In fiict, thcsc nrcas coniprisc tlic tliornicst formations found in a11 of South Africa - tlic so-cilllcd "subtropical thicket" - which arc virtually inipcnctrablc in plnccs. Parts of the subtropical tliickct show tlic grcatcst riclincss in succulcnts within tlic soutlicrn African suiiinicr rainfall region. Tlicsc arc tlic Noorsvcld and Vallcy Bushvcld (Enstcm Capc) and to a lcsscr extent the Arid Buslivcld of Eastcrn Transvaal and nortlicrn Natal. Tlic Noorsvcld is cliariictcrizcd by tlic prcdoniinant 1-2 ni tall. ccrcoid Eirpliorbio cocrirlcsccrrs ("noors"), but thcrc arc many niorc succulcnts which tcndto liidc undcr or inside of spincsccnt shrubs. Floristically thc vcgctation is sonicwliat intcrnicdiatc bctwccn that of thc Succulcnt Karoo and itrid savanna.

AFRO-TE~~PEKATE GRASSIAND AND FORESTS

Afro-tcmpcratc vcgctation occurs on tlic liighcr Drakcnsbcrg and Maluti Mountains (Lcsotlio) in an arca of roughly 233,000 kni2. Tlic winter climatc is cold with regular licavy frost and occasional snow. Rain falls mainly in suniiiicr and ranges bctwccn 600 and 2000 iiini pcr annuni. Fircs ilrc an alniost yearly occurrcncc. Coniparcd to tlic othcr regions tlic succulcnt flora is poor: only 85 spccics havc bccn rccordcd from Lcsotlio (JACOT GUILLARMOD, I97 1 ) . Typical grassland succulcnts includc Eiipliorfio prrlriiinrti, tt, claw-ioirlcs, Knlcrrichoc fliyrsijlom, Crossrrlo copitello ssp. norlirlosa, C. sai-cocnrrlis, hlossiri irircrrrillrrris and grass alocs. Tiic shcltcrcd kloofs of thc castcrn and southcrn slopcs of tlic soutlicrn and castcrn niountains coniprisc afro-tcnipcratc forest. Afro- tcnipcratc forcsts rcacli thcir climax at Knysna and Gcorgc near tlic coast in tlic castcrn corner of thc Wcstcrn Cape Provincc (South Africa). Tlicsc dcnsc forcsts consist mainly of tall trccs such as Porlocorpus, Olirrio, Kiggeloriri, Crrrtisio and Cirnnoiiia. Succulcnts

GIORNALE BOTANIC0 ITALIAN0 - VOLUME 129. I . 1995 413

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

arc only occasionally found, c.g. Pcperottiia, Begotiin, Plcctrntitliirs, Crnssirla spccics and somctimcs Aloe nrborescctis which arc typically found in tlic forcst margins and in cxposcd rocky habitats. In rclation to thc othcr major regions this is thc poorest in succulcnt spccics.

REPRESENTATION AND DISTRIBUTION OF THE SUCCULENT FLORA

TAXOSOWC REPRESENTATION

About 8% of thc worlds cstiniatcd 250,000 flowcring plant spccics occur in South Africa and Namibia which covcr a surfacc arc8 of about two niillion h i2 . Of tlic South African and Namibian plant spccics 3665 or 17% arc succulcnt (595 spccics from Namibia alonc, KOLBERG ct nl., 1992). Most of thc southcrn African succulcnt spccics arc conccntratcd in tlic Succulcnt Karoo (Grcatcr Capcnsis) of tlic scriii arid to arid winter rainfall rcgion in an cstiniatcd arca of about 80 000 kni2. As mcntioncd above, this rcgion has bccn rccognizcd both as a formation of zonal iniportancc and a phytochorion of its own (Lcaf Succulcnt Zone, JURGENS, 1986; 1990; 1991). Thc south African succulcnt plant spccics arc rcprcscntcd in 45 plant faniilics of wliicli 9 faniilics (414 spccics) bclong to tlic Monocotylcdonac and 34 faniilics (3152 spccics) to the Dicotylcdonac. By far thc largcst family are thc hlcscriibryantliciiiaccac with sonic 1350 spccics currently cstiniatcd (HARTMANN, 1991). A list of thc succulcnt spccics is providcd in an appcndix.

REPRESENI-ATION INTHE REGIONS

Thc majority (65%) of succulcnt spccics occur in thc scnii-arid arcas of the Grcatcr Capcnsis (Lcaf Succulcnt Zone): Tlic sccond highcst proportion of 23% is found in thc Savanna rcgion in castcrn and northcrn South Africa and northcrn Namibia. Tiic Nania- Karoo is relatively poor in succulcnts with nicrcly 9%. although it is tlic sccond Iargcst rcgion in tcrnis of surfacc arca. Tiic lowcst proportion is rccordcd from thc Afro-tcnipcratc grassland and forests with only 3%. Altliougli thc Grcatcr Capcnsis conipriscs the largcst proportion of succulcnt spccics, thcsc arc taxononiically confined to 17 faniilics. only. Tlic highcst divcrsity is contributcd by hlcscnibryantlicniaccac and Crassulaccac with liigli lcvcls of local cndcniisni. This is intlicativc of favorablc local spcciation conditions during thc past and considcrablc gcograpliic isolation. Convcrscly. thc niodcratc succulcnt spccics divcrsity of thc Savanna rcgion is rcprcscntcd out of 36 faniilics. Tiic incidcncc of cndcniism is lowcr and many spccics cxtcnd tlicir distribution areas into tropical Africa.

CENTRES OF DIVERSITY

As nicntioncd abovc, tlic Succulcnt Karoo stands out as an arca with thc grcatcst richncss in succulents. Within this region tlic lcvcl of divcrsity and cndcriiisni is particularly high in ii nunibcr of sniall arcas wliicli have frcqucntly bccn recognized as "ccntrcs of divcrsity and/or cndciiiisni" (HARTMANN. 1991 ; HILTOK-TAYLOR, 1987; JURGENS, 1986; 1991; NORDENSTAM. 1969; WEIhlARCK, 1941; WERGER, 1978b). Thcsc include tlic "Garicp Ccntrc" of thc Riclitcrsvcld, tlic "Vanrliynsdorp Ccntrc" of thc Kncrsvlaktc and thc "Littlc Karoo Centre". Ccntrcs of Succulcnt Karoo taxa outsidc tlic Succulcnt Karoo include thc "Pofadtlcr Ccntrc". situatcd in tlic vicinity of Pofaddcr and Warnibad at thc bordcr bctwccn Namibia and South Africa, tlic "Uppcr Orangc Ccntrc" strctcliing frorii Griqualand to tlic southern parts of thc Orangc Frcc Statc. and thc "Albany Ccntrc" in thc Eastern Capc Provincc (all South Africa). In thcsc arcas tlic taxa arc niostly liniitcd to azonal habitats, likc rocky outcrops, and salinc pans (scc Jurgcns 1991 for bricf rcvicw and furthcr rcfcrcnccs). Bcsidc tlicsc karroid links, a nunibcr of

451 GIORNALE BOTANIC0 ITALIAN0 - VOLUME 129. I , 1995

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

succulcnt taxa of thc castcrn Capc show subtropical and tropical phytogcographic affinitics (HOFFMAN Br COWLING, 1991). In thc summer rainfall rcgion thc grcatcst succulcnt richcs of zonal occurrcncc ("Stcni Succulcnt Zonc", JURGENS, 1986) arc found in thc subtropical savanna rcgions (Noorsvcld, Vallcy and Arid Bushvcld, ACOCKS, 1953) of thc low intcmiontanc vallcys of thc castcrn Capc, Natal and rcgions of castcrn and northcrn Transvaal and Namibia.

SUCCULENT LIFE AND GRO\\'TH FORhIS

In thc following tlic succulcnt spccics of thc study arca arc assigncd to tlic tlircc basic lifc fomis "lcaf succiiIcntstt, %cm succulcnts" and "gcophytcs". Thc proportion arc GG% lcaf succulcnts, 26% stcni succulcnts and 8% gcophytcs. Tlic high figurc of lcaf succulcnts clcarly rcflccts tlic cxtrcnic spccics richncss of thc Lcaf Succulcnt Zonc of thc Grcatcr Capcnsis. Most rcniarkablc is the distribution of thc lcaf vcrsus stcm succulcntsinsidc and outsidc of thc Grcatcr Capcnsis. Of thc total nuriibcr of lcaf succulcnts spccics. 79% occur in tlic Grcatcr Capcnsis. particularly in thc Succulcnt Karoo, coniparcd to 21% found in thc rcniaining rcgions. In contrast, tlic lattcr coniprisc 63% of tlic total nunibcr of stcni succulcnts, coniparcd to 37% occurring in thc Grcatcr Capcnsis. Thcsc figurcs arc dircctly rclatcd to tlic diffcrcnt climatic rcginics (SCC Jurgcns 1986 for dctails): Thc lcaf succulcnts arc mostly activc thc cool wintcr rainfall scason. Convcrscly, thc largc orthotropic cactoid and ccrcoid stcni succulcnts in particular, arc confincd to tlic wami and hot subtropical rcgion and its outlaycrs. Stcni succulcnt growth forms arc largcly prcscnt in habitats of strong conipctition by fast-growing non- succulcnts. particularly (mainly C4!) grasscs (GIBRS RUSSELL, 1988). or in thosc arcas whicli arc subjcct to high tcriipcraturcs o r low liuniidity conibincd with low but rcgular prccipitation (JURGENS, 1986). In tlic Lcaf Succulcnt Zonc. on thc otlicr hand. stcni succulcnts arc sniallcr, likc ninny stapclins. In this regard i t is rcniarkablc that tlic highcst spccics conccntration of tlic tribc Stapclicac (Asclcpiadaccac) is found in tlic transitional zonc along tlic castcrn bordcr of tlic arid wintcr rainfall rcgion (ALRERS cf 01.. 1989). In thc widcsprcad stcni succulcnt gcnus Hoodicr (Asclcpiadaccac) thc tallcst growth fomis arc found in northcrn Naniibia (BRUYNS, 1993). In tlic Icaf-succolcnt gcnus Arincnrrrpscros Portulacaccac) tlic hottcst localitics arc inhabitcd by tlic nicnibcrs of thc scction Avonia which arc charactcrizcd by a stcni-succulcnt-likc habit (GERBAULET, 1992a). Thcsc rclations bccomc also appnrcnt from thc rcprcscntation of arborcsccnt growth fomis: thcrc arc 107 arborcsccnt south African succulcnt spccics (3% of tlic succulcnt flora) rcaching 2 ni in liciglit or highcr. Of tlicsc only 12% arc found in thc Grcatcr Capcnsis, whilst 88% occur in tlic subtropical Savanna and Nania-Karoo rcgions conibincd. Furthcmiorc. 79% of tlic arborcsccnt spccics arc stcni succulcnt, whcrcas only 21 % arc lcaf succulcnt. Most of thc lattcr group cxliibit a combination of (oftcn dcciduous) succulcnt lcavcs and stcnis, whilc thc rcriiaining spccics arc tall woody shrubs. In contrast to tlic gcncral trcnd in tlic distribution of stcni succulcnts, JURGENS (1986) found that tlic fruticosc chaniacphytic nicnibcrs o f tlic Mcscnibrynnthcniaccac (out of 22 gcncra) arc clcarly ccntcrcd in tlic soutliwcstcrn part of soutlicrn Africa, wiiilc poorly branclicd, low growing compact chaniacpliytcs ("contractcd" chaniacphytcs) (out of 2 I gcncra) arc most promincnt in tlic ccntral iind southcrn parts of South Africa and tlic southcm corncr of Naniibia. an arca \vhich is largcly situatcd outsidc of tlic wintcr rainfall rcgion. Thc succulcnt spccics with clinibing shoots whicli contributc 5% of thc total succulcnt flora arc iiiostly (95%) confincd to thc Savanna and forcst rcgions, whilst only 3% occur in thc Grcatcr Capcnsis and 2% in thc Nania-Karoo. I t can bc concludcd that clinibcrs arc niost favourcd in thc dcnsc and high plant fomiation of tlic subtropical rcgion. Morcovcr, 61% of thc succulcnt climbcrs havc succulcnt tubcrs, roots or caudiccs, whilst only 13% dcvclop an acrial succulcnt stcni; 8% can bc assigncd to tlic group of lcaf succulcnts. Faniilics with a major proportion of clinibcrs includc thc Cucurbitaccac (48 spp., 28%), Asclcpiadaccac

GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129. I , 1995 445

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

(46 spp., 27%), Vitaccac (33 spp.. 19%). Dioscorcaccac (19 spp., 11%) and Passifloraccac (7 spp., 4%).

CAhlOUFU\GE AND ARhlAhlENT

Spincsccncc, caniouflagc and chcniical substanccs arc widcsprcad fcaturcs among the southcm African succulcnts convcying "dcfcncc" or "ncutral rcsistancc" (EDWARDS, 1989) against hcrbivory. Within thc study arca as a wholc, camouflage appears to bc the most succcssful stratcgy to avoid hcrbivory, with 24% of tlic spccics total falling undcr this category. About 16% wcrc idcntificd to posscs phytoclicniical dctcrrcnts and 9% to cmploy mechanical dcfcnsc rncchanisms. Thc perhaps bcst known cxamplcs of camouflagc arc tlic "living stoncs" of tlic gcncra Litlrops, Lopidorin, or Coriophytrrrii which avoid dctcction by mimicking tlic surrounding substrata (cryptic mimicry or crypsis). The niastcrs of dcccption arc, howcvcr, thosc spccics which allow thcnisclvcs to bc covcrcd by thc substrata itsclf, citlicr by going coniplctcly underground (c.g. Fcncstrnriu) or by exuding sticky substanccs on thc acrial parts onto which soil particlcs adhcrc, c.g. Psnnirirophoru (all Mcscnibryanthcmaccac). Howcvcr, sonic of tlic charactcristics conveying camouflagc may also bc of valuc in lowcring watcr loss through transpiration or in rcducing radiation and hcat. Particularly in voluniinous succulcnt lcavcs a thick and flcxiblc, xcroniorpliic skin is a prcrcquisitc for shrinking niovcnicnts (c.g. in Otlroriiin opiiiin, JURGENS. 1986). thus providing stability as an "cxoskclcton" (Ihlcnfcldt 1989). With regard to (anti-)hcrbivory, such compound fcaturcs havc bccn classificd as "ncutral rcsistancc", as opposcd to spccific ltdcfcncctt convcycd by poisonous sccondary nictabolics or spincsccncc (EDWARDS, 1989). In anotlicr group of caniouflagc plants thc lcavcs arc furnishcd with a niottlcd colouring andlor soft appcndagcs which visually dissolvcs thcir charactcristic shapc and outlinc froni tlic distancc (c.g. Gnstcrin, Hnworllrin. Fnircorin). Such adaptions can bc cxpcctcd to work niost cfficicntly in habitats with dcnsc vcgctation. But cvcn in thc niorc opcn arid rangclands many plants grow tuckcd away within usually non-succulcnt buslics, thus, lowcring visibility and acccssibility. Exaniplcs includc thc highly palatablc, soft-woodcd scraniblcrs of thc gcnus Trichotlintlcrir~r and niorc tough-skinned. sonictinics spiny, low growing stcm succulcnt Stapclicac. Morcovcr. scarccncss vcrsus abundancc of plants might havc iniplications to\vards Iicrbivory, in that scarcc spccics arc niorc likcly to "avoid1' hcrbivory. Howcvcr, a scattcrcd occurrcncc or cscaping undcr "protcctivc" shrubs might bc niorc closcly rclatcd to disscniination (GERDAULET, 1992a) or rccruitnicnt pattern (YEATON R: ESLER, 1990). Again, in tlic abscncc of niorc conclusivc data, it appears ncarly inipossiblc to distinguish bctwccn causc and cffcct and to quantify tlic incidcncc of gcnuinc caniouflagc. Camouflagc succulcnts as rccognizcd licrc appcar to bc niost succcssful in tlic Nania-Kiiroo (54% of thc rcgional succulcnt flora), followcd by tlic Savanna rcgion (33%) and tlic Grcatcr Capcnsis (14%). Tlic rcprcscntation for spccics with phytochcniical dcfcnsc nicclianisnis is possibly undcrratcd, sincc inforniation on sucii dctcrrcnts is gcncrally inconclusivc or abscnt for most Mcscmbryilntlicniaccac (scc HARTMANN, 1991). On thc onc Iiand, tannins whicli quantitativcly rcducc tlic digcstability of plant tissucs arc prcscnt in thosc Ruscliioidcac with long-livcd xcroniorpliic Icavcs, but arc abscnt in thc rcniaining Ruscliioidcac and hlcscmbryantlicnioidcac with short-livcd or dcciduous lcavcs and in annuals (HARThIANK, 1991). with thc notable cxccption of thc annual gcnus Hyiiicnogync (IHLENFELDT gL GERDAULET, 1990). On thc othcr hand, scvcral nicnibcrs of tlic lattcr group wcrc tcstcd positivc for alkaloids (HERRE. 1971). Thcsc findings appcar to bc in linc with both tlic I'apparcncy thcory" (FEENY, 1976) and tlic "rcsourcc availability thcory" (COLEY ct 01.. 1985). given a slow growthhigh rclativc invcstnicnt ratc for tlic "tannin" group vcrsus a fast growtldlow rclativc invcstmcnt rate for thc "alkaloid" group (scc IHLENFELDT, 1985, 1989). Othcr succulcnts may lowcr hcrbivory simply by having

416 GIORNALE BOTANIC0 ITALIAN0 - VOLUME 129, 1. 1995

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

a low nutritional value. Possiblc candidatcs would bc ~ifeserrrbryarrfhcrrrrrri~ subgcn. Cryoplrytum spccics with cxtrcmcly low phytornass pcrccntagcs (VON WILLERT ef al., 1990) and high contcnts of accuniulatcd salt (c.g. VON WILLERT et nl.. 1979, 1990. DE VILLIERS, 1995). Howcvcr. spccics of thc samc taxon tcstcd also positive for alkaloids (HERRE, 1971). Notwithstanding tlicsc complications, it can bc assumcd that nicscmbs havc a gcncrally low nutritive valuc. In fact, not a singlc mcrnbcr of thc Mcscrnbryanthcmaccac is mcntioncd in a rcccnt list of 100 (highly to Icss) palatablc ficld plant spccics compilcd by thc South African Dcpartmcnt of Agricultural Dcvclopmcnt (BREDA gL BARNARD, 1991). On thc rcgional lcvcl thc poisonous succulcnt componcnt is niorc or less lcvcl within thc Grcatcr Capcnsis (14%), Nania-Karoo (15%) and Savanna rcgion ( 1 6%). On thc othcr hand, thc catcgorization of spincsccncc (tlspincs" uscd hcrc as a gcncral tcrm which includcs "thorns" and "pricklcs", scc GRURR, 1992) as a gcnuinc anti-herbivore dcfcncc mcchanisni scerns niore straightforward. Within thc southcrn African context spincs arc sccn as a protcctivc nicclianisni against both hcrbivory (siniilar to poisonous phytochcniicals) as wcll as trampling and breaking by nianinialian hcrbivorcs (in contrast to phytochcniicals) (MILTON, 1991, scc GRUBR, 1992 for furthcr purposcs). On tlic rcgional lcvcl spincsccnt succulcnts account for 12% in tlic Grcatcr Capcnsis. 21% in tlic Nania-Karoo and 25% in tlic Savanna rcgion. MILTON (1991). on thc othcr hand. found a gcncral lcvcl of about 10% spincsccncc within regional floras sclcctcd from most of southcrn Africa. I t thus appears tliat succulcnts of thc Nania-Knroo and Savanna rcgion fomi a subsct within thc flora with a distinctly highcr incidcncc of spincsccncc. This is. howcvcr. not corroboratcd by MILTON (1991) who found such a corrclation to bc statistically insignificant. Ncvcrthclcss, thcrc sccnis to bc a rclation bctwccn spincsccncc and lifc forni in that spincs arc most oftcn associatcd with stcni succulcncy. In stcni succulcnts spincs niay bc bornc on thc stcnis (c.g. Eriplrorbin, Pncliyporliirnr. Snrcacnrrlori, scvcral Asclcpiadaccac) or along thc leaf margins (Aloe). Convcrscly, truly spincsccnt spccics arc rcniarkably rarc in lcaf succulcnts. In a couplc of spccics of tlic gcnus Phyllobolus and its closc alliancc tlic lcaf niiddlc vein bcconics niorc or lcss lignified and pcrsists as a spiny structurc (GERBAULET in prcp. a). Howcvcr, thcsc thorns arc mostly fairly brittlc and do not appcar to bc vcry protcctivc against hcrbivory. Morcovcr, a fcwspccics prcviously nssigncd to thc gcnus Ebcrloti:in, dcvclop niorc or lcss spiny inflorcsccnccs or purc "inspincsccnccs" by abortion of flowcr buds carly during ontogcny (HARTMANN 8r STURER. 1993). Thc rcsulting thorns may bc stout, most notably so in Rrrscliin subgcn. Spbosac and Ebcr1orr:in sfylosn (tlic lattcr of iinccrtain taxononiic position) or brittlc. Pcrsistcnt but blunt spincsccnt structurcs which arc only fornicd aftcr tlic abscission of fruits arc known from Drosnrrthcrrrrar, hifcstoklcriia and Aridorin spccics (GERRAULET in prcp. b, HARThlANN & STOHER, 1993). Thcsc spincs probably forni resistant "pcriphic c a p . " in oldcr plants, rathcr than thrcatcning spincs. Thc ecological and cvolutionary intcrprctation of thc distribution pattcrns of thc spiny succulcnts is prccludcd by contradictory cvidcncc. A fcw cxaniplcs takcn from thc spiny nicscnibs may cxcmplify thc point: In hcr abovc-nicntioncd survey on spincsccnt plants in arid southcrn Africa MILTON ( I 991) found tliat spincsccncc tcndcd to incrcllsc with aridity. Ivhilc this gcncral trcnd is followcd in c.g. thc gcnus Lcipoldtia (thc spiny spccics occur in niorc arid ilrcas than thcir non-spiny countcrparts), this is not thc casc in c.g. Krrschicr subgcn. Spinosac; thc first is rcstrictcd to thc arid part of the wintcr rainfall rcgion, thc lattcr occurs undcr all rainfall rcginics in southcrn Namibia and throughout thc \vcstcm half of South Africa (DEHN, 1992; HARTMANN Br STUBER, 1993). Whilc thc distribution of thc spiny nicscnibs conccntratcs along thc castcrn bordcr of thc wintcr rainfall rcgion and furthcmiorc in thc adjaccnt interior parts of thc central platcau, only onc of thcsc spccics occurs in onc of thc arcas (in thc Naniib Dcscrt) idcntificd as "high spincsccncc nodcl' by MILTON ( 1 991 ). Thc highcst spccics frcqucncy pcr quarter dcgrcc grid area is found bctwccn 30" and 31's and 19" to 19'30'E just on thc border of thc wintcr rainfall area

GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129, I . 1995 447

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

(HARThlANN Br STUBER, 1993). This is rcmarkablc in that this particular area shows a low frequency for Mcscnibryanthcmaccac as a wholc and othcr succulents in gcncral (JURGENS, 1986; HARTMANN. 1991). Wiilc certain spccics arc largcly inipalatablc and may bc highly abundant in ovcrgrazcd and dcgradcd rangclands, otlicrs appear to bc palatablc for livcstock (HARThlANN & STUBER, 1993).

CONCLUSIONS

From thc prcscnt rcvicw on thc rcprcscntation and distribution of soutlicrn African succulcnts thc following trends bcconic obvious:

- Thc highest divcrsity and cndcmism of succulcnts is found in tlic rcgion of thc Grcatcr Capcnsis, particularly thc Succulcnt Karoo. In this part, tlic succulcnt flora is doniinarcd. by Mcscmbryanthcniaccac, in tcniis of both taxononiic divcrsity and plant cover.

- Thcrc is a dichotomy in thc occurrcncc of leaf vcrsus stcni succulcnts which largcly coincides with tlic border linc of the winter rainfall region.

- Outside of thc Grcatcr Capcnsis Icaf succulents arc gcnerallyconfincd to azonal habitats. Morcovcr, at lcast in tlic Mcscmbryanthcniaccac. spccics with azonal occurrcncc show a prcdoniinancc in compact life fornis and bclong to tnxononiic groups which arc absent froni thc Grcatcr Capcnsis. On thc othcr hand, cactoid, ccrcoid and caulcsccnt stcni succulents arc largcly absent froni tlic Grcatcr Capcnsis; within this rcgion stcni succulcnts usually show low growth forms oftcn hidden in co-occuring shrubs.

- Particularly notcworthy is tlic liigli incidcncc of spincsccncc in tlic stcni succulcnt coniponcnt. Convcrscly, lcaf succulents arc cliaractcrizcd by an abscncc of dcfcncc nicchanisnis. but rathcr by nicchanisni of "ncutral rcsistancc" and a generally low nutritive valuc for herbivores. In thc Nania-Karoo leaf succulcnts show a particularly high proportion of camouflagcd spccics.

Ackrioii~lcrlgerirerrrs . - Wc thank Maikc Gcrbaulct for valuable coninicnts on thc manuscript.

REFERENCES

ACOCKS J. P. H., 1953 - Veld Types of Sortrlr Africa. Mcnioirs of thc 13otanica.l Survcy of southcrn Africa 40: 1-128.

ALDERS F., DELFS W.. K U S C I ~ G. 6: h k V E U.. 1989 - Lcberisforrrterr der Ceropegieac wid Srapelieae (Asclepidiaceae) i r i crrideri Zorierr Afiikas. Hcitrsgc zur Biologic dcr Pflanzcn

ARNOLD T. El. 6: DE WET C., 1993 - Platits of soitlherri Africcr: riurircs urid rlislribitriori.

I ~ A Y E R M. B., 1984 - The Crrpe Florrr r r r d thc Kuroo - (i ii.irirer ririr&ill biorire iw -s i ts a Fjrrbos

BInKIct{ V. R: HARTLIANN H., I988 - The Airoacerrc - a rieiv approaclr. Botanical Journal of

130~0 P. 6: GOLDDLATT P., 1984 - Plnrrrs of die Cope Flora. A descripriw ccrtrrlo,oitc. Journal

I ~ R E D A P. A. R. R: BAHNARD S. A., 1991 - Veld Plarils of /he Writer Rnirifull KcZion.

I3 R U Y N S P.. I993 - A rei*isioii of Hoodia cir id Lar.r-ariia (Asclepiorlaccne - Srupelicrie).

COI.EY P. D.. BRYANT J. P. 6: C H A P I N F. S., 1985 - Hcsortrcc availability arid plorit

C O ~ I I T O N R. H.. 1976 - The Flora of Sii~o:ilriricl. Journal of SouthAfrican Botany I I: 1-684. CO\\'l.ISG R. M. 6: .HILTON-TAYLOR C.. 1993 - I'orrerns of p h i / c/ii*crsiry orid errderrrisrir iri

soirllrerri Afiica: air oiwr.icn*. In: HUNTLEY B. J. (Ed.) Botanical Divcrsity in Southern

64: 59-74.

Mcnioirs of thc Botanical Survcy of southcrn Aliica 62: 1-825.

biorire. Vcld 6: Flora 70: 17-19.

thc Linncan Socicty 97: 239-254.

of South African Botany Supplcmcntary Volunic 13: 1-455.

Dcpartmcnt of Agricultural Dcvclopmcnt Rullctin 422: 1-21 I .

Hotanischc Jahrbiichcr fur Systcmatik I 15: 145-270.

arr/ilrerbii-ore rlefcricc. Scicncc 230: 895-899.

41s GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129. I , 1995

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

Africa, pp. 3 1-52. Strclitzia I , National Botanical Institutc, Capc Town. - 8: HOL~IES P. M., 1992 -Flora arid vegerariori. In: COWLING, R. M. (Ed.) The Ecology of

Fynbos. h’iitrierirs, Fire and Diversity. Oxford Univcrsity Prcss. Capc Town. D E H N hi.. 1992 - Untersitcliioigcri ziini Verwandrscha frskreis der Rtiscliiinae

(~fcscrribrjarir/ier~iaceae Fetid). hlittcilungcn aus dcm lnstitut fur Allgcrncinc I3otanik Ilarnburg 21: 91-198.

DE V I L L I E R S A. J., 1995 - Reriioral of sodiiini arid chloride froni a snlirie soil 6 y rllesernbryarirheriiririi borklyi. Journal of Arid Environmcnts 29: 325-330.

EDWARDS P. J., 1989 - Insect herbii*ory and plarir defence rlieory. In: GRUBII P. J. 8: WHITTAKER J. B. (Eds) Towards a Afore E.mcr Ecology, pp. 275-297. Blackwcll Scicntific Publications, Oxford.

FEENY P., I976 - Platit apparericy arid clicrtiical defcrisc. Rcccnt Advanccs in Phytochcrnistry

GERnAULET M., I9923 - Die Gollirng Anocarripseros L. (Porriilacaceoc). I . Urirersricliiingcri air Sjsrcrriarik. Botanischc Jahrbuchcr fur Systcmatik I 13: 477-564.

- , I992b. Die Garriirig Arirrcariipscros L . (Porriilocaceae). 11. Urirersircliirrigoi ;rir

Biogeograpliic. Botanischc Jahrbuchcr fur Systcniatik I 13: 565-576. - , in prcp. a. Rcvisiori of the geriiis Plijlloboliis N.E.Ur. I3otanischc Jahrbuchcr fur

Systcniatik. - , in prcp. b. Kcvisiori of / l ie geriirs Aridaria N.E.Hr. Hotanischc Jahrbuchcr fur

Systcrnatik. Gibbs-Russcll G. E.. I987 - Prelirriiriary jlorisric arioljsis of rlic rirajor Oiorrics iri soirrlierri

Africa. Bothalia 17.2: 213-227. - , 1988 - Disrribirriori of siibfartiilies arid tribes of Poaccac iri sorirlicrri Africa. hlorlerii

sjsicriioiic sriidics in Africari bornriy. hlonographs in Systcmatic Botany 25: 555- 566.

- , RETIEF: E. 8: ShtoOK L.. 1984. Iriroisiry of Plaril Colleclirig i r i Soiirlierri Africtr. Bothalia 15. I 8: 2: 131-138.

GRUnB P. J.. 1992 - A posirive disrrrrsl iri simplicity - lessoris fiorri plaril deferices arid frorri corripcririori nrrrorig plorirs arid ariiorig ariiriids. Journal of Ecology 80: 585-6 10.

HAKGREAVES H. J.. 1990 - The Siiccrilerirs of Hoisic*oria. Ari AririoriredCliccklisr. National Muscunis, MonumcHartmann H.E.K. 1991. hlcscmbryanthcrna. Contributions froni thc Bolus Hcrbariurn 13: 75-157.

HARTL~ANN H. E. K. 8: STUBER D., 1993 - 011 rlie spiriy ~leseriibr~cirirlrcrrra arid rlie g e m s E6crlari:io (Ai:oaceae). Srirdies of rlre Aleseriibrjari~liertia (Aizoocene). Contributions from thc Ihlus Hcrbariurn 15: 1-75.

t i E R R E H., 1971 - Poisorioiis ~feseriibr~orillierrrccne. In: HERRE H. (Ed.) Tlrc Goicra of rlie Alcserirbryarirlieriiccae. p. 37. Tafclbcrg, Capc Town.

tiILTON-TAYLOR c., 1987. I’hylogeogrophy n r i d origiris of rlie Karoo Jhro. In: COWLlSG R. AM. R: Roux P. W. (Eds.) The koroo biorire: (I preliriiiriory sjriiliesis. Port 2. Vegeroriori arid 1iisror-y. South African National Scicntific Prograiiimcs Rcport 142: 70-95. CSIR. Pretoria.

HOFFhlAN M. T. 8: CO\VLI~’G R. hl., 199 I - P/ijioc/ioro/ogy arid erirlerriisrii dorig ciricliry arid grazirig grmlierirs i r i /lie lowcr Siirirlajr River Volley, Soiirli A friccr: irirplicaiioris for vegc/rrriori hislory. Journal of Biogcography 18: 189-201.

IHLENFELDT H. D.. I985 - Le6errsforrireri irr id iiberlebcrissrro~cgieri bei Sirkkit/eriroi. Ikrichtc dcr Dcutschcn Botanischcn Gcscllschalt 98: 409423.

- , 1989. Li/e srnilcgics of siicciilerir rlcscrr plarirs. Excclsa 14: 75-83. - 8: GERUAULET hI., 1990 - Urircrsircliiiiigeri zrrrii nfcrkrrrrrlsbcsiciri~l iiri i l air Ta.wnoriiie

tier Gnrriirigoi Apotesia h’.E.Br.. Carl)arirlieri N.E.Br.. Coriicosia A’.E.llr., IIcrrea Sclinwrires i r r i d fljriicriogyric tiail.. (~leser~ibryari~hcriinceric F e d ) . liotanischc Jahrbiichcr fur Systcmatik I I I : 457-498.

10: 1-40.

JACOT GUlLLhRhtoD A. F. M. F., 197 I - Flora of Lesorho. J.Crarncr, Lchrc. JURGENS N., I986 - Urircrsriclrirrigoi : / i f Okologie sirkkiilerircr Pjluri:c~i tles siirlliclies Afiika.

hlittcilungcn aus dcrn lnstitut fur Allgcmcinc Botanik Hamburg 2 I : 139-365. - , I990 - Renrarks ori rlie 6iogeogrcrpliy of hleseriibrj~irirlicr~iciceac arid rlieir possible

irsc iri other ririd regioris. hlittcilungcn aus dcrn lnstitut fur AIIgcmcinc Botanik Ihnburg 23B: 1047-1060.

- , 1991 - A riew approach 10 I I I C h’orriib Regiori. Par! I : I’hyrogcogrrrpliic

GIORNALE BOTANIC0 ITALIAN0 - VOLUSIE 129. I . 1995 439

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014

sii6divisions. Vcgetatio 97: 2 1-38.

species. Dintcria 22: 1 - 12 I .

selecliori by rnarninals? Occologia 87: 279-287.

Botanica 23: 1-77.

Govcmrncnt Printer. Prctoria.

categorization. Mcmoirs of thc Botanical Survey of southcrn Africa 5 4 1-98.

H. F., HERhfAN P. P. J.. RETIEF E., SLIITHIES s. J. 8: WELhlhN W. G., 1993 - Soitt/i African sircciilerit plarirs - nri irpclared sjnopsis. Aloc 30,2: 3 1-74.

TAKHTAJAN A., 1986 - Nor i s r i c regions of tlic world. Univcrsity of California Prcss, Bcrkclcy.

VAN DER SCHIJFF H. P., 1969 - A c/rcck-lisr of die vascrdar plarils of the Kriigcr National Park. Publication of thc Univcrsity of Prctoria no 53.

VAN JAAKSVELD E. J., I987 - The sriccrrlcrii riches of Soirth Africa arid Arairri6ia. Aloc 24: 45- 9 2 .

- 8: COWLING S., 1994 - The Sircciilenrjlora of the greater Cape Peiiirisitla. Aloc 31, I: 1-30.

VAN ROOYEN N., VAN RENSWRG D. J.. THERON P. 8: DU BOShlA J., 1988 - Clrecklisr of Floweririg ploiits of the Kalahari Cernslok Park. Kocdoc 3 I: I 15-135.

VAN WIJK P.. 1974 - Sorirc van die A'osiotiale Krirgerwilltitin. Part 2. Pcrskor. VON WILLERT D. J., D R I N C K ~ I A N N E. 8: SCHULZE E.-D., 1979 - E c o p l i y s i o l o i c n l

inr*csrigatioris of plar i rs in tlre coastal desert of soirthcrti Africa. In: JEFFRIES R. L. 8: DAVY A. J. (Eds.) Ecological processes in coastal cnvirorirrieriis, p. 32 I . Ulack\ \~ l l , Oxford.

/if.. strategies. Vcgctatio 90: 133 143. - , -. -. - R: H.-D. IHLENFELDT. 1992 - LijC Siratcgics of Siiccirlcrits in Deserts, wirlr

special rcfcwncc to tlic Notirib clescrt. Cambridge Univcrsity Prcss, Carnbridgc. W E I ~ I A R C K H., I94 I - PIijtogeographicaI grorips, CCI I I~CS an~l i i i ter ids ~cirli iri tlic Cape j lora.

\VERGER h.1. J. A.. 19783 - ~iogcograp/r ical divisions of Soiiilrern Aji-ica. In: WERGER M. J. A. (Ed.) Hiogeographp arid Ecology of Soirrlrerri Africa, pp. 145-170. W. Junk, Thc Hague. , 1978b - The Karoo Arari1i6 Rcgiori. In: \VERGER M. J. A. (Ed.) Iliogcograp/iy and Ecology of Soirrlrcrri Africa. pp. 23 1-299. \V. Junk. Thc Haguc.

KOLBERG H., GIESS W., MOLLER M. A. N. 8: STROHBACH B., 1992 -List ofNamibian plant

MILTON S. J., 199 1 - Planr spinescence iii ar id soirtherri Africa:cloes rrioistiire nicdiarc

NORDENSTAM B.. 1969 - Phytogeogrophy of the senits Eirrjops (Conipositoe). Opera

R O S S J. H.. 1972 - The Flora of Natal. Deportment of Africitltirral Teclitiical Services.

RUTHERFORD hf. C. 8: WESTFALL R . H.. 1986 - Biorncs of Soiiiherri Africa - on o6jectir*e

ShllTH G. F., HOBSON S. R., MEYER N. L.. CHESSELET P., ARCHER R . H., BURGOYNE P. M.. GLEN

- , ELLER R . M., \VERGER M. J. A. 8: BRINCKLIANN E.. 1990 - Desert JiiCCIf/Clils atid their

. Lunds Univcrsitcts Arsskrift 37, 5: 1-143.

-

WHITE F., 1983 - Tlie vegetcrtiori ofAfrica. UNESCO, Paris. YEATON R. 1. 6: ESLER K . J.. 1990 - The rlytiornics ofsitccirlcrir karoo ~~cgetatiori. Vcgctatio

88: 103-1 13.

450 GIORNALE BOTANIC0 ITALIAN0 - VOLUhlE 129. I . 1995

Dow

nloa

ded

by [

Uni

vers

ity o

f A

uckl

and

Lib

rary

] at

14:

08 1

7 D

ecem

ber

2014