Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
STUDIES IN THE CALENDULEAE
499
B. P h y togeøgraphical d i s t r i b u t i o n suggest i n g
the c e n tres of o rigi n o f t h e g e n e r a.
As far as I am avvare, no fossils or casts of plant remains have vet
been found that cail be idenlified with extant or closely related species
of Calenduleae. Thus, the question of the linie and place at which the
tribe arose is at present unanswerable. None of the species grow 011
swampv ground, where relics of plants are most easily preserved for
posteritv. Most of the species, 011 the conlrary, are found in möre or
less arid regions. The plant remains of this |ribe that have the greatest
cliance of heilig preserved in deposits, are the achenes, for they have
a thick. bard pericarp. Winged achenes, which occur in many
Calendula and Osteospermum species, may very well have been carried by
the wind lo swampv places, where they becanie embedded as fossils.
It is therefore very likely that fossil achenes of Calenduleae will be
identified in fulure investigalions.
The Cichoriae already occur in deposits from the Lower Oligocene
of Aix in Southern France. The complete absence of fossils of the
Calenduleae in these deposits is regarded bv Small as evidence t ha I this
|ribe developed at a låter date than the Cichoriae. As Aix-en-Provence
is situatecl in the peripliery of the distribution area of the
Calenduleae. |here is however liardlv any reason lo expecl fossils of the
tribe at this locality, even if it had been differentiated during the
Oligocene. The genus Calendula has certainly developed in North Africa, and
il is verv improbable that il had spread so far north as France al
that linie.
Small (1919 p. 205) considers that Dimorphotheca and Tripteris
were differentiated during the Lower Pliocene. This assuniption seems
verv likely, but lie cannot adduce any very weiglity evidence of this.
He locates the origin of the tribe Calenduleae lo South Africa, and
writes (I.e. p. 26): »The South African centre for this tribe and ils
marked restriction in area, in addition lo ils close similarity lo Ihe
Senecioneae in morphology and phvsiology, suggest an origin from
the South African Senecioninae al a date even möre recenl than that
of the origin of the Cichoriae .
The view |bat Ihe Calenduleae is a branch of Ihe Senecioninae’s
genealogical Iree is not likely to be contested by anyone. As regards
the generic and specific differentiation, the tribe Cjdendideae has ils
cliief cenlre in South Africa at the present linie. There the
morphological ly most primitive lypes are found, hilt there occur hesides a large
<< prev. page << föreg. sida << >> nästa sida >> next page >>
