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476
TYCHO NOR LINDH
genus Calendula and Ihe South African Osteospermum. Its soutliern
limit is in the equatorial region, at approximately 3- 4 S.. where the
widespread species Osteospermum monocephalum and
Chrysanthe-moides monilifera have their northernmost outliers. Thence and to
British Somaliland Osteospermum Vaillantii is the onlv representative
of the tribe Calenduleae. Then comes Osteospermum muricatum in the
mountains of British Somaliland.
In the mountain areas of northern and eastern Abyssinia O.
Vaillantii has been collected in many places. Ön the other hand, it is
un-known from the mountains of southern Abyssinia, where it should be
able to thrive as well as ön the mountains in the equatorial region.
Thus the species shows a large gap in its distribution between the
central portion of Abyssinia and the mountains south of Lake Rudolph.
As a matter of fact, this gap may not be by any means so large as the
map indicates (map fig. 2). When southern Abyssinia has been möre
tlio-roughly explored O. Vaillantii will probably be discovered in several
localities tliere. It is unlikely that it will be met with in the Rudolph
depression, however.
The lower country separating the mountains and highlands in
Kenya Colony from those in Abyssinia is designated the Rudolph
inter-val (Weimarck 1941). At the present time |here are nol favourable
climatic conditions in this area for O. Vaillantii, but during an earlier
climatic period this species had no doubt a fairly continuous
distribution from the mountains in Kenya Colony to those in Abyssinia.
This species, which is of such significance from a
phytogeogra-phical point of view, sends from Abyssinia one branch to the north
up into Calendula’s distribution area (map fig. 1) and one to the east
over British Somaliland to Socotra. 11 also occurs ön the other side of
the Gulf of Aden in the mountains of the Yemen togetlier with
Osteospermum muricatum and Calendula aegijptiaca.
The second important link in the connection between the chief
centres of the tribe Calenduleae is Osteospermum monocephalum (map
fig. 2). In East Africa, which primarily interests us here, it extends
from the central part of Southern Rhodesia up iniö Tanganyika
Territory. Its northernmost outlier is situated between Ihe north end of Lake
Tanganyika and Lake Victoria. This species especially occurs ön steppes
and savannas, descending right down to an altitude of c. 1000 m.
According lo the map, O. monocephalum exhibits several large
inter-vals. Its Zambesi interval is undoubtedly correct but, ön the other hand,
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