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482
TYCHO NOR LINDH
3. The Interrelation of the Genera and their Centres of Origin.
The problem of the relationships of 1 lie tri be Calenduleae with
other tribes belonging lo the Compositae will not be dealt with in this
chapter, but will be discussed låter in a Ireatise ön the morphology of
the tribe. My intention here is to attempt to give a survey of the
interrelation and the evolutionary liistory of the genera in the tribe with
the aid of morphological and phytogeographical data.
A. Morphological characters i n d i c a t i n g
interrelation and various phyletic 1 i n e s in the tribe.
The interrelationship of the genera in the tribe Canduleae is int.
al. indicated by the absence of paleae or other appendages ön the
receptacle and of pappus ön the aclienes. These two negative characters
are very important in delimiting this tribe from some other tribes in
the family.
In my opinion the pre-Ccdenduleae ancestors were furnished with
both receptacular paleae and pappus. Gradual reductions have caused
the paleae and pappus to disappear entirely or almost entirely. In a
few species möre or less distinct rudiments of these organs are found.
Occasional individuals of a species, e.g. Osteospermum glabrum
(I p. 170), may have a quite distinct selose pappus ön the ovaries, but
this probably always falls off before the fruit altains maturity. Such
atavisms must of course be taken as evidence that the ancestors of the
species were once lipon a linie normally equipped with a pappus. Thus
the present species may be regarded as morphologically reduced.
Paleae which suhlend the individual florets ön the receptacle are
no doubt homologous to the involucral bracts. The pappus is generally
regarded as a modified calyx-limb. A few botanists consider, however,
that the pappus is not homologous to a calyx-limb, bul that it is a
trichome structure (Small 1918).
Sexual differences of Ihe florets in the capitulum have been used
lo a great extent by various authors for the distinction of genera. The
taxonomic value of these characters varies in different tribes. I have,
although with some hesitation, used these differences and ihose in the
pistil when separating Dimorphotheca from Osteospermum, and acting
lipon the same principles I have had to revive the old genus Castalis
for some species previously belonging lo Dimorphotheca.
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