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478
TYCHO NOR LINDH
Lake Nyasa is presumably also much larger than that shown ön
the map.
The third important connecting species is Chrysanthemoides
mo-nilifera. This polymorphous species reaches from down in the Cape
right up into Tanganyika Territory to the neighbourhood of
Kiliman-jaro, where it encounters Osteospermum Vaillantii. Like Osteospermum
monocephalum il presents a number of möre or less large intervals
(map fig. 3). The cliief of these are the Limpopo and Zambesi
intervals, which are certainly correct. The intervals north of these may
very well be due to lack of investigation. In any case these gaps in the
distribution may be expected to be considerably reduced when research
is låter carried 011 in these parts.
The Ihree connecting species menlioned above are rich in
bio-types and they are thus able to thrive under quite a wide range of
different ecological conditions. They possess a good capacityr of seed
dispersal, and their extensive distribution is 110 doubt mainly due to
this. Osteospermum Vaillantii and O. monocephalum, which belong to
the subgenus Tripteris, have winged achenes that are dispersed by the
wind. Chrysanthemoides monilifera has drupes which are eaten bv
birds and through tlieir agency are spread far and wide.
Besides these Ihree species, which directly link the centra of the
tribe Calenduleae to each other, Osteospermum Volkensii and 0.
muri-catum are of very great in terest, suggesting, as they do, an earlier and
better connection between the centres of the tribe over tropical East
Africa. Both of these species belong to the subgenus Euosteospermum.
As already mentioned, Osteospermum Volkensii is known onlv
from Kilimanjaro (map fig. 4) and may be regarded as an epibiotic
species. According to Volkens, it is one of the commonest plants at the
upper limit of the primeval forest (I p. 122). Il is a shrub 1—3 metres
in height, occurring at an altitude of from 1700—4300 metres. The
achenes not being winged, the dispersal capacity of the plant is
na-turally low compared with that of preceding species.
Morphologically, O. Volkensii is nearest allied lo O. herbaceum,
which is found in the south-eastern littoral districts of South Africa
(I map p. 406). These are the only two species belonging lo the well
delimited section Oppositifolia. Düring an earlier period, presumably
the Tertiary, the phylogenetic stock from which O. Volkensii and
O. herbaceum have developed will probably have had a continuous
distribution extending from Soulh Africa up into tropical East Africa.
In consequence of climatic changes and probably also of keen competi-
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