Agriculture Reference
In-Depth Information
As was the case in California, the equable conditions along the coast during the
early Miocene supported temperate and tropical forest elements and few repre-
sentatives of fynbos sclerophylls (Coetzee & Muller
1984
). Pollen evidence shows
that by middle Miocene these coastal riverine sites were gallery forests of mixed
tropical forest but with fynbos well established in the area, despite the presumed
winter drought, summer rain climate (Coetzee & Rogers
1982
).We lack much of a
Miocene record from interior, and potentially more arid and climatically seasonal
sites thought to be sites of early fynbos evolution (Axelrod & Raven
1978
). An
early origin of fynbos taxa is necessary to support many of the patterns of
speciation evident from molecular studies.
Although it has long been the belief that speciation in both the Cape of South
Africa and southwestern Australian sclerophyll shrublands is largely a recent
phenomenon, this is not true for many lineages (Edwards & Hawkins
2007
;
Hopper
et al.
2009
; Sauquet
et al.
2009a
). For example, it appears that much
of the present diversity in the Cape MTV is the result of recruiting diverse lineages
over the entire Tertiary, such as several clades of Iridaceae,
Pelargonium
(Geraniaceae), and
Indigofera
(Fabaceae) (Linder
2005
),
Muraltia
(Polygalaceae)
(Forest
et al.
2007
),
Protea
(Valente
et al.
2009
), and the legume tribe Podalyrieae
(Boatwright
et al.
2008
). It is estimated that 60% of the Cape flora originated in
the Tertiary and the remainder in the Quaternary (Linder & Hardy
2004
),
although the vast majority have apparent origins within the last 10 Ma (Verboom
et al.
2009
). Other prominent South African taxa such as the Ericaceae were
apparently absent in the region until late Miocene and so a more recent radiation
is inferred (Deacon
et al.
1983
). Molecular clock estimates for the Poaceae
Ehrharta
indicate most speciation was confined to the Miocene and Pliocene
(Verboom
et al.
2003
) and Quaternary radiations are evident in the Brassicaceae
Heliophila
(Linder
2005
; Mummenhoff
et al.
2005
).
Within lineages dominant in both Australia and South Africa such as the
Restionaceae, the radiation appears to have started substantially earlier in Aus-
tralia. Rates of lineage accumulation have been constant since the early Tertiary in
Australia whereas there was a Miocene acceleration in the Cape, differences
perhaps due to different geomorphological histories (Linder
et al.
2003
). Eocene
to early Oligocene radiations are also evident in Australian
Eucalyptus
, Casuar-
inaceae and
Banksia
, suggesting Australian radiations were earlier than South
African radiations (Linder
2005
). In the Haemodoraceae both regions are charac-
terized by pulses of speciation since middle Miocene (Hopper
2009
). Although the
southwest Australian flora is more phylogenetically diverse, it includes numerous
lineages with low diversification rates (Sauquet
et al.
2009b
).
Thus, the present-day MTV Gondwana landscape comprises a mix of lineages
with Tertiary radiations and with Quaternary radiations, as well as Tertiary relicts
that failed to radiate (Hopper & Gioia
2004
; Linder
2005
; Hopper
et al.
2009
).
Gradual increases in seasonally dry conditions during the Miocene and lack of
any single trigger seem to characterize radiation of these southern hemisphere
MTC floras (Linder
2005
). While this may be true overall, another way to express
