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502
TYCHO NOR LINDH
genus mav also be distinguished, namely in the eastern part of the
Mediterranen ii region.
Jndging by the concentration of the species, the Cape region is the
primary centre of evolution for the Calenduleae in the southern
hemisphere. In several of South Africa’s other floral regions there are,
however, important secondary centres of evolution for the tribe, for
instance in the Namaqiia region and the Drakensberg.
The genera Dimorpliotheca, Castalis and Chrysanthemoides have
no marked gene centre in any of South Africa’s regions. (iibbaria, ön
the contrary, is almost entirely confined to the Cape region. The largesl
genus in the tribe, Osteospermum, has its centre in the Cape region.
lf one studies the geographica! distribution of the species in t lie two
subgenera of Osteospermum, only Eiiosteospermum proves to have its
centre located in the Cape region, whereas Tripteris has a stronger
concentration of its species in the semi-arid areas lo the north of the
Cape region, viz. in Ihe Nainaqua region.
Excellent proof of the pre-Calenduleae ancestors having had a very
wide distribution in past times, is the occurrence of an endemic
Osteospermum species ön Si. Helena. The population from which O.
Sanctae-Helenae has developed has certainly lived isolated 011 S|. Helena since
the Tertiary. In morphological characters this interesting species
fils best into seel. Xenismia, where it comes nearest to O.
acanthosper-mum, which occurs in Lillie Namaqualand, the distance being c. 2850
km from St. Helena. O. Sanctae-Helenae also comes near to the
poly-morphoiis South African species O. calendulaeeum, which forms a
section of its own, Oliyocarpus.
The distribution of seel. Xenismia is verv remarkable, for its three
species spread over areas that are verv remote from each other, viz.
South Africa (together with the south of Angola and X. Rhodesia),
St. Helena, Brit. Somaliland and the Yemen. I assume tliat
Osteospermum Sanctae-Ilelenae, O. acanthospermum, O. muricatum and also
O. calendulaccum in seel. Oliyocarpus have differenliated from a
poly-inorphous syngameon, which had a very large, continuous distribution
during the Tertiary, and then especially during semi-arid periods. for
all these species are markedly xerophilous.
In regard lo the shape of the achenes, O. Sanctae-Helenae is
probablv considerably reduced. The achenes are provided with
out-growths of irregulär shape (I p. 182, fig. 17 1), and these appear to be
incomplelely developed. The species closely allied to O. Sanctae-Helenae,
viz. O. acanthospermum (I p. 182, fig. 17 a) and O. muricatum (I p. 182,
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