Agriculture Reference
In-Depth Information
gymnosperms. However, serotiny is restricted to just a few conifers in California
and the Mediterranean Basin (Bond
1985
; Lamont
et al
.,
1991
). It is particularly
common in the proteoid shrubs that form the overstory of many fynbos commu-
nities (species of
Protea
,
Leucadendron
,
Aulax
in the Proteaceae;
Box 7.1
). There
are also serotinous members of the Asteraceae, Bruniaceae, Ericaceae, Rosaceae
Box 7.1 Proteaceae
This family is almost exclusively in the southern hemisphere and comprises
about 80 genera and 2000 species of mostly woody evergreen plants. It provides
a striking example of adaptive radiation. There are several genera with more
than 50 species and some with more than 350 species (
Grevillea
). Many species
produce very showy inflorescences, consisting of many small flowers densely
packed into a compact head or spike, and have been used extensively for
ornamental purposes (
Fig. B7.1.1
). Flowers are usually pollinated by insects
and birds, and more rarely by bats and small marsupials (Myerscough
et al.
2000
).
Banksia
and
Protea
are iconic species of Australia and South Africa,
which are the main centers of diversification (
Fig. B7.1.2
), although there are
marked differences in diversity patterns of this family between these regions
(Cowling & Lamont
1998
).
Proteaceae occur on virtually every land mass in the southern hemisphere
(including New Zealand, New Caledonia, New Guinea and South America),
reflecting an ancient Gondwana origin. The traditional vicariance biogeo-
graphical view was that Proteaceae taxa drifted along with the Gondwana
fragments and thus became distributed throughout all ancient Gondwana
lands. However, recent phylogenetic analyses suggest that some nodes associ-
ated with transoceanic disjunctions postdate the breakup of Gondwana
(Barker
et al.
2007
). If correct, then the current distribution of Proteaceae is
explained by a combination of vicariance and long-distance dispersal between
continents.
Proteaceae are well adapted to the two prominent characteristics of Austra-
lian and South African MTC landscapes: fire and infertile soils. Many species
(with the exception of the most basal genera, e.g.
Agastachys
,
Symphionema
, and
the subfamily Pesoonioideae;
Fig. B7.1.2
) possess a characteristic root struc-
ture, called proteoid roots, especially efficient in poor-nutrient soils. Proteaceae
also shows a large variety of adaptive fire traits. Serotiny (see
Fig. 3.5
) appears
in species with fruits that are formed of woody follicles (e.g.
Banksia
,
Hakea
,
Lambertia
,
Xylomelum
). It also appears in species with small one-seeded achenes
that are held between persistent bracts tightly clustered in oval or globular
heads (e.g.
Petrophile
,
Isopogon
). Indeed, Proteaceae is the family that includes
most of the serotinous species worldwide. Seed dormancy and fire-stimulated
germination is observed in some species of
Conospermum
,
Grevillea
,
Persoonia
with soil-stored seeds (Myerscough
et al.
2000
). Fire-stimulated flowering has
Continued
