5.3 Class Magnoliopsida – flowering plants - Cambridge University ...

5.3.5 Basal flowering plants and Eumagnoliids
At the base of the flowering-plant phylogenetic tree there is a diverse
group of families a ‘grade rather than a clade’ with a high proportion
of primitive or unspecialised character states, fascinating
because they represent the relicts of an early stage of flowering plant
evolution.
Table 5.4 The distribution of features of flowering plants
In basal groups
(primitive/plesiomorphic/unspecialised)
5.3 CLASS MAGNOLIOPSIDA – FLOWERING PLANTS 227
Features in high frequency
In derived groups
(advanced/apomorphic/specialised)
Small shrubs, lianes or rhizomatous perennial
herbs, or aquatics and semi-aquatics
Various but including annuals and tall trees and herbs
Vesselless Vessels present
Parts in whorls or spirals of variable numbers Parts in whorls of three, four or five
Actinomorphic Actinomorphic or Zygomorphic
Parts free Parts connate or adnate
Stamens broad with poor differentiation between
filament and anther
Stamens with well-differentiated filament
Apocarpous Syncarpous
Unsealed stigma and poorly differentiated style Sealed stigma with well-differentiated style
Follicles Fruits (various)
amborellales
DNA sequence data places a plant called Amborella trichopoda from
New Caledonia in a basal position as a sister to all other flowering
plants. This is not to say that it is the ancestor of all other flowering
plants. Rather that it is the closest living relative of the ancestor and
like all other living flowering plants it exhibits a mixture of primitive
and derived features. It is a shrubby evergreen plant with simple
leaves that may be lobed. It has tracheids but no vessel elements. It is
dioecious with flowers grouped in axillary cymose inflorescences. It
has a perianth consisting of five to eight undifferentiated segments
that are weakly joined at the base and are arranged in a spiral. The
male flower has numerous (10--25) laminar stamens, the outer fused
to the base of the perianth segments. Pollen is aperturate to nonaperturate
and sulcate with a granulate outer wall and is possibly
not tectate, a feature of possibly great significance. The female flower
has five to six free carpels in a whorl. Carpels are open at the tip
and have one ovule. Seeds are endospermic and the embryo has two
cotyledons.
(a)
(c)
(b)
Figure 5.57. Amborella: (a) plant;
(b) male flower; (c) female flower.