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498
TYCHO NOKLINDH
have developed, liiere is. however, no difficulty in dislinguishing lhem,
for Osteospermum calendulaceum never has annulate achenes. whereas
such entirelv predominate in the heads of C.alendula aegy ptiaca. The
distribution areas of Ihese species are widelv remote.
Before proceeding lo the mainly phytogeographical part of the
chapter, I will give a brief sunnnary of my views about the evolution
in the tribe (cf. the phylogenetic chart, p. 497).
All the species populations from which the recent Culenduleae have
arisen, have at one time passed through stages of evolution in which
they were provided with receptacular paleae, pappus, and 9-fertile ray
as well as disc florets.
By a reduclion process that affected paleae and pappus, the tribe
Culenduleae crystallized ont first as a primitive Dimorphotheca, i.e.
the tribe comprised, to begin with. only such species as produced hoth
ray and disc achenes. These achenes were probably of a simple type
compared with those in most species of the recent Culenduleae.
This primitive Dimorphotheca had a wide, continuous distribution
from the Mediterranean lo the Cape. Its extension from north to south
was presumably already during the Tertiary mainly Ihe same as it is
at the present time, but ils connection over tropical Africa was much
heiter developed Iben than now. Evidence of this is provided, int. al.,
by an epibiotic species, Osteospermum Volkensii, ön Kilimanjaro.
By successive reductions of the pistils eil her in the disc or in the
ray florets, the subsequent evolution has branched in two direclions
from Ihis primitive Dimorphotheca, and just a lew species in the tribe
suggest that this evolution is still going ön. New genera have
differen-tiated from the primitive Dimorphotheca and, during the course of
linie, this basal genus has thereby much decreased hoth as regards Ihe
number of species and the geographica! distribution. Dimorphotheca
may be regarded as a transilional genus. At the present linie, il
coni-prises only a lew species. whose extension is confined lo South Africa
and Angola.
In addition lo Ulis regressive evolution of the organs of
fructifica-tion in Ihe ray or disc florets, there has taken place within the tribe
a very strong differentiation into different fru i l lypes. In most cases.
the möre complicated fruit types may, as 1 have pointed ont above, be
derived from cerlain simple types through a series of intennediate
forms. A number of möre or less continuous form series of fru its suggests
different phyletic lines in the tribe.
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