Bothalia 11,1 & 2: 177-180 (1973)
Notes on the phytogeographical affinities of the southern Kalahari
M. J. A. W E R G E R *
ABSTRACT
The chorological division o f southern Africa as proposed by W hite (1965, 1971) and Volk (1966) is
discussed. Reference is made to distribution patterns o f some typical K aroo-N am ib taxa as discussed
by Volk and to the rem arkable distribution of disjunct taxa in the arid zones o f Africa. On the basis
thereof and of the similarity in the floras o f the southern K alahari and the K aroo-N am ib Region,
the conclusion is draw n th at the chorological division as proposed by Volk (1966) seems justified.
In the early days o f phytogeography, chorological
units were distinguished on extrem ely fragm entary
evidence. F o r instance, G risebach (1872) based his
classification o f the vegetation o f the w orld largely
on the inform ation extracted from the lim ited num ber
of diaries o f early travellers an d adventurers. A frica
was divided by him in to the follow ing five fioristically
and physiognom ically defined vegetation areas:
M editerranean, Sahara, S udan, K alahari and Cape.
His Sudan area covers m ost o f su b sah aran A frica,
whereas the K alah ari com prises South-W est A frica,
Botswana and m ost o f the T ransvaal an d the O range
Free State. H e regarded the O range R iver as the
boundary betw een the K alah ari and C ape areas, a
decision he based o n B urchell's observations. Sub­
sequently extensive collections o f h erb ariu m m aterial
have contributed decisively to alter an d refine th e
chorological classification o f the w orld. T hus, p ro ­
gressing from the w ork o f pioneers like Engler,
Lebrun and others, in recent years a fairly satisfac­
tory phytogeographical classification o f the A frican
continent has been achieved. M onod (1957) dis­
tinguished three m ajo r chorological units o r “ groupes”
in Africa: the M editerran ean group, the tropical
African group and the C ape group. T he tropical
African group he subdivided into fo u r regions: I
region soudano-angolane, II région guineo-congolaise, III région afro-alpine, an d IV région K arro o Namib. He fu rth er subdivided the S udano-A ngolan
Region into three types, th e S ah aran Type covering
North A frica, the Sahelian Type covering S ub­
saharan N o rth A frica, E th io p ia, E ast A frica, and
parts o f R hodesia, B otsw ana, A ngola, S outh-W est
Africa and South A frica, an d th e S udanian Type,
covering the zone betw een the previous type and the
West and C entral A frican rain fo rest zone. His
Sahelian Type is again subdivided in to a north ern
and a southern p a rt, th e la tte r o f w hich com prises
the K alahari, the T ran sv aal Lowveld and Bushveld,
and the H ighveld. W ithin the K a ro o -N a m ib region
Monod (1957) recognized three D om ains: the K arroo
Domain, com prising the area th a t is also geographi­
cally indentified w ith th a t nam e except the coastal
zone; the N a m aq u alan d D om ain , com prising a
narrow inland zone in S outh W est A frica along the
escarpment, tap erin g o u t on th e so u th ern p a rt o f
the Angolan co ast; an d th e N am ib D o m ain , covering
the entire arid w inter rainfall area o f South A frica
and the N am ib desert.
* Botanical Research Institute, D epartm ent o f Agricultural
Technical Services, Private Bag X101, Pretoria.
5292-12
This phytogeographical division o f A frica was
largely accepted by W hite (1965, 1971) and V olk
(1966). W hite m odified M o n o d ’s classification in so
far as he renam ed the S udano-A ngolan Region to
the Sudano-Z am bezian Region. He further regarded
the n o rth ern Sahelian zone as an im poverished
w estern extension o f the O riental D om ain into the
S udanian D om ain, w hereas he com bined the southern
Sahelian zone with M o n o d 's A ngolo-Z am bezian
D om ain into the Z am bezian D om ain o f the SudanoZam bezian Region. Besides the A fro-A lpine R egion,
W hite also distinguished an A fro-M ontane Region
(Fig. I).
It is generally accepted th a t the C entral K alah ari
has closer fioristic affinities with the Z am bezian
D om ain an d should be incorporated into the SudanoZam bezian R egion, rath e r than into the K aro o N am ib Region (B rem ekam p, 1935; M onod, 1957;
M endonca. 1961; W hite, 1965, 1971; Volk, 1966).
W hite (1965) discussed the distribution o f the tree
species o f the savannas and w oodlands o f the Z a m ­
bezian D om ain. H e found th a t in the K alahari this
w oody flora is poorly represented, and th a t the
species usually occur as shrubs, whereas they form
well-developed trees in the adjacent p art o f the
Zam bezian D om ain. H e suggested the K alahari is
transitional between the Sudano-Z am bezian and
K aro o -N am ib R egions, b u t included it on his m ap
in the form er Region. L ater, W hite (1971) accentuated
this point, and drew the boundary between the tw o
Regions w ithin S outh A frica and South W est A frica
ju st n o rth o f the O range River and from there
northw ards to southern A ngola (Fig. 1). T hus, the
south-w estern bou n d ry between the two Regions
coincided closely with the distribution boundary o f
Acacia haematoxylon. Volk (1966) accepted W hite’s
chorological division except for this south-w estern
b ou n d ary betw een the K aro o -N am ib and the SudanoZ am bezian Regions. He (Volk, 1964, 1966) discussed
the d istribution o f several species belonging to w hat
he called the A fro-M eridional-O ccidental floral
elem ent, and thus supplied evidence fo r his suggestion
to include the area o f the Southern K alahari as
delineated by Leistner (1967) into the K aroo-N am ib
Region. Besides his discussion on the distribution o f
Rhigozum trichotomum, Stipagrostis ciliata, Parkinsonia africana. Aloe dichotoma, Stipagrostis hochstetterana. Acacia haematoxylon and Sesamothamnus
guerichii, w hich he considered typical for the A froM eridional-O ccidental o r K aroo-N am ib Region, Volk
listed a considerable num ber o f endemic, m onotypic
PH Y TO G EO G RA PH IC A L A FFIN ITIES O F T H E SO U TH ER N K ALA H A RI
178
Sc
c / Concur
THE PHYTOGEOGRAPHICAL
REGIONS OF AFRICA
Mediterranean
I
Sahara - Sinc/ian
II
Sudano- 2-ombezian
a • Sudan/on Domain
O » Oriental Domain
s o - Sahelian extkneian of
Oriental Domain
2
ST
- Zambezian Domain
Ctuir> *o - Congo!i a r t
UsZ» Uaambara-Zululand
Domain.
ST
Karroo Namib
21
Cap*
ED
Afro- montane
VIII Afro-alpine (not mhoyvn)
IX
A fa cJ o g a a ca r
o r small genera th a t characterize this Region. Based
upon this evidence, he drew the b o u n d ary between
the S udano-Z am bezian an d the K aro o -N am ib Regions
north-east o f the so u th ern K alahari, the western
K alahari T hornveld an d the V ryburg S hrub Bushveld
(Volk, 1966) (Fig. 2).
A p art from the distrib u tio n p attern s discussed by
V olk, there is an o th er im p o rtan t feature o f the
flora o f the southern K alah ari th a t su p p o rts its
inclusion in the K aro o -N am ib Region. As pointed out
by Range (1932), De W inter (1966, 1971), V erdcourt
(1969) and particularly by M onod (1971), a large
num ber o f taxa th a t occur in the K aro o -N am ib
Region also occur in the north ern Sahelian zone, the
O riental D om ain and the S aharo-Sindian R egion. In
southern A frica these disjunct tax a occur in the
K aro o -N am ib Region as delineated by W hite (1971)
as well as in the areas th a t Volk (1966) has additionally
included in this R egion. H ow ever, these tax a are
absent o r virtually so in the rem ainder p art o f the
Z am bezian D om ain as delineated by Volk (Fig. 2).
R ecently T olm achev (1971) pointed o u t th a t, in
various floras o f the sam e floristic region, the sequence
o f im portance o f those families th a t com prise m ost
o f the species o f a flora is rem arkably constant.
Also the percentages o f species co n trib u ted to a
flora by these fam ilies are fairly co n stan t. This is
independent o f the to tal num ber o f species o f a flora
o r the extent o f its area. These prem ises provide a
1 .— Phytogeographical
Regions of Africa according
to W hite (from White,
1971).
F ig .
m eans o f testing the floristic affinity o f the southern
K alahari with the tw o floristic Regions in question.
Since A cocks’s Veld Types (1953) are floristically
well-circum scribed units (com p. G runow & M orris,
1969), and rath e r com plete species lists o f several
Veld Types are available, they provide a suitable
basis fo r a com parison o f their floristic com position
with th a t o f the southern K alahari. T herefore, the
com position o f the flora o f the southern K alahari,
based on the check-list produced by Leistner (1967),
and a species list o f the V ryburg Shrub Bushveld
with invading K a ro o species [A cocks, Veld Type
17 (2)], was com pared w ith the floras o f the K arroid
Broken Veld (A cocks, Veld Type 26), the C entral
U pper K aro o (A cocks, Veld Type 27), the A rid
K aroo (A cocks, Veld Type 29) and the O range River
Broken Veld (A cocks, Veld Type 32) as floras that
form p art o f the K a ro o -N am ib R egion, an d with
the flora o f the C entral variation o f the Bankenveld
(A cocks, Veld Type 61,b), the flora o f the Jack Scott
N atu re Reserve, located in the Bankenveld (Coetzee,
1972), and the flora o f the P retoria m agisterial
district (B .R .I., n.d.), as floras th a t form p art o f the
Zam bezian D om ain o f the S udano-Z am bezianR egion.
The num bers o f species o f the first nine families
th a t contribute the m ost species to their floras are
show n in percentages in Tables 1, 2 an d 3.
M . J. A. W E R G E R
I Mediterranean
H Saharo - Sindian
HI Sudano - Zambezian.
S * 5udanian Domain
0 “ Oriental Domain
sa* 5aKalian extension of
Oriental Domain
Z • Zambezian Domain
H Guineo - Congolian
Y. K.artao-Nar«ib
21 Cape
•
2. —Phytogeographical
Regions o f Africa according
to Volk (from Volk, 1966).
F ig .
Afro-Montane
0 Afro-Alpine and Afro- Montane
TABLE 1.—K aroo-N am ib Region (num ber o f species per
family as percent)
Flora of Veld Type
Total No. o f species
26
1 195
27
715
29
523
32
974
Asteraceae.....................
Poaceae..........................
Aizoaceae......................
Liliaceae........................
Scrophulariaceae..........
Fabaceae........................
Chenopodiaceae...........
Asclepiadaceae.............
Crassulaceae.................
Sterculiaceae.................
Euphorbiaceae.............
17,9
8 ,4
20,7
11,1
4 ,4
6 ,9
9,1
5 ,3
2 ,9
2,7
—
2 ,5
16,8
9 ,8
9 ,4
—
2,2
2 .4
—
5 ,2
4 ,8
3,4
3,1
—
3,1
—
13,5
9,5
7 ,6
7,6
5,3
5 ,0
—
3,5
3 ,0
T o tal..................
63,2
63,1
63,8
8,0
4 ,8
3,6
—
2,6
10,8
8,2
—
2 ,9
57,9
From the tables it can firstly be noted th a t all the
floras discussed have a strik in g sim ilarity. A m ongst
the m ost im p o rta n t nine fam ilies, several are shared
by all the floras. A lso, th e to tal percentage o f species
contributed to their floras by these first nine families
is rather sim ilar, a lth o u g h th ere tends to be a decrease
in this figure from th e m ore tem p erate floras in the
south-western p art o f S o u th A frica to w ard s the m ore
tropical n o rth -eastern floras.
TABLE 2. — Southern K alahari and Vryburg Shrub Bushveld
(N um ber o f species per family as percent)
S. K alahari
438
Flora
T otal N o. o f species
12,6
P oaceae...............
A steraceae...........
Fabaceae.............
Liliaceae..............
Aizoaceae............
Scrophulariaceae.
S terculiaceae.. . .
A sclepiadaceae...
C u cu rb itaceae...
E u p h o rb iac eae...
T o ta l.........
TABLE
17(2)
709
14,3
5 ,9
7 ,5
5.1
3 .7
3.1
2 .7
___2 , 4 ^
57X
3.—Zam bezian D om ain (N um ber of species per
family as percent)
Flora
61 ,b
T otal N o. o f species
Poaceae..............................
A steraceae.........................
Fabaceae............................
Liliaceae.............................
Cyperaceae........................
Asclepiadaceae..................
Scrophulariaceae..............
R ubiaceae..........................
E uphorbiaceae..................
T o tal...........................
P retoria
m.d.
1 045
J. Scott
N .R.
522
13,2
14,7
7,8
5,2
4 ,8
3 ,6
3,3
2 .4
2 ,2
57,2
16,1
12,3
6,7
5,4
4 ,2
2,7
2,5
2 ,7
2,3
54,9
13,2
10,7
8 ,9
4,1
4 ,5
5 ,2
1 666
2,8
2,3
2,3
54,0
180
PH Y T O G E O G R A PH IC A L A FFIN ITIES O F T H E SO U TH ER N K A LA H A R I
O f the fo u r floras o f the K aro o -N am ib Region
com pared, the first fo u r fam ilies listed are the same,
although their sequence differs slightly. T here is
som e variation in fam ilies th a t are sixth to ninth in
the sequence. T he C entral U p p er an d the Arid
K aroos have the C henopodiaceae and the S tercu­
liaceae in com m on, w hereas these fam ilies contribute
respectively 1 ,9 % and 1 ,8 % o f the to tal num b er o f
species in the flora o f the K arro id Broken Veld, and
respectively 1 ,9 % an d 2 ,1 % in the flora o f the
O range R iver B roken Veld. The family A sclepiadaceae
is absent from the first nine families o f the flora o f the
C entral U p p er K aro o , where it only scores 1 ,5 % .
C rassulaceae is absent from the list o f the A rid
K aroo, w here it scores 1 ,3 % , and E uphorbiaceae
scores 1 ,4 % an d 1 ,7 % in the floras o f the C entral
U pper an d A rid K aro o s respectively.
Table 2 o f the floras o f the S outhern K alahari
and the V ryburg S hrub Bushveld shows a strong
sim ilarity with Table I o f the K aro o -N am ib Region.
Poaceae, A steraceae, Fabaceae, Liliaceae, A izoaceae,
Scrophulariaceae, Sterculiaceae, A sclepiadaceae and
E uphorbiaceae reappear am ongst the im p o rtan t
families, an d the only m ajo r differences are the ap ­
pearance o f the C ucurbitaceae in the list o f the
S outhern K alah ari an d the absence o f C henopodiaceae
and C rassulaceae, although it should be rem arked
th a t the C henopodiaceae scored the sam e value as
E uphorb iaceae in the S outhern K alahari.
Table 3 o f the floras o f the Z am bezian D om ain is
considerably different from T ables 1 and 2. In all
three lists represented in T able 3, the nine m ost
im p o rtan t fam ilies are the sam e an d occur in virtually
the sam e sequence. R em arkable is the ap p earance o f
the Cyperaceae an d the R ubiaceae am ongst these
nine m ost im p o rta n t families. In the floras o f T able 1
these tw o fam ilies only scored betw een 0 ,6 % an d
1 ,8 % an d betw een 0 ,6 % an d 1 ,3 % respectively,
w hereas in the floras o f T able 2 these values were
between 1 ,4 % and 1 ,7 % an d between 1 ,0 % and
1 ,6 % respectively. O th er rem arkable differences
between Tables 1 an d 2 on the one h an d an d T able 3
on the o th er are the low er values scored by the
Liliaceae an d particularly the absence o f A izoaceae
in T able 3. A izoaceae scored only betw een 0 ,2 %
and 0 ,8 % in the floras o f T able 3. C henopodiaceae,
Sterculiaceae an d C rassulaceae also scored low
values here.
I t is clear th a t com parison o f the floras o f the
three different areas leads to the conclusion, th a t the
floras o f the so u th ern K alah ari an d the V ryburg
Shrub Bushveld have considerably greater affinities
with those o f the K aro o -N am ib Region th an w ith
those o f the Z am bezian D om ain o f the SudanoZam bezian R egion.
Thus, based upon the results o f the com parison
o f floristic sim ilarity, the distrib u tio n o f the disjunct
arid taxa an d distrib u tio n p attern s o f several typical
taxa as discussed by Volk (1964, 1966), V olk’s
(1966) inclusion o f the southern K alahari an d the
V ryburg Shrub Bushveld in the K aro o -N am ib Region
seems fully justified.
A C K N O W L ED G E M E N T
I am very much indebted to M r J. P. H. Acocks
for his kindness in providing me w ith his unpublished
checklists o f six Veld Types and to M r B. J. Coetzee
fo r m aking available to m e his unpublished checklist
o f the Jack S cott N atu re Reserve.
OPSOMMING
Die plantegeografiese indeling van suidelike A frika
soos deur W hite (1965, 1971) en Volk (1966) vo o r­
gestel, w ord bespreek. D a a r w ord verwys na die
verspreidingspatrone van som m ige tipiese K arooN am ib taksa, soos hulle deur Volk bespreek word.
O ok w ord d a a r verwys na die opvallende ver­
spreidingspatrone van die disjunkte taksa o o r die
droë sones van A frika. O p grond hiervan en van die
ooreenkom s in die floras van die suidelike K alah ari
en die K aroo-N am ib Streek w ord afgelei, d a t die
plantegeografiese indeling soos voorgestel deur Volk
(1966), geregverdig lyk.
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