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

Basal Eudicots
Basal eudicots such as the Proteales and Ranunculales have a pattern
of leaf venation in which the lateral veins terminate at the margin in
a small tooth (craspedodromus). They have a well-developed perianth
but this is poorly differentiated into a calyx and corolla, and has a
variable number of tepals spirally arranged or in whorls of three. Stamens
and carpels are numerous and varying in number. The carpels
are free to connate and have a sessile stigma.
ranunculales (buttercups, poppies and barberries)
Evolutionary trends in the Ranunculales include changes in the symmetry
and the increasing complexity of the flower. Floral parts,
especially the numerous stamens and carpels are commonly spirally
arranged and the fruit is usually a follicle or an achene. The
flower is apocarpous with superior pistils. The poppies, Papaveraceae
(∼660 species) are derived from the buttercups from which they
differ by having a syncarpous gynoecium and only two to three
sepals. There are two subfamilies, the actinomorphic Papaveroideae,
which produce latex, and the strongly zygomorphic Fumarioideae,
which have a clear sap. Another large family in the order, the
Berberidaceae (∼570 species) is distinguished from the Ranunculaceae
by having stamens opposite the petals and a single pistil
which becomes a berry. They have their flower parts in whorls rather
than a spiral with two whorls of stamens and one to two whorls of
nectaries.
proteales (proteas, banksia and grevilleas)
The Proteales are well represented in the Southern Hemisphere. The
family Proteaceae in particular shows a distribution which records
the old Gondwanan supercontinent. The Proteaceae are one important
family (Figure 5.82) where brush blossoms have evolved. Some
relationships discovered by the analysis of DNA sequence data are
distinctly odd. For example, in the Proteales, Nelumbo, the sacred
lotus, and Platanus, the plane tree, are sister groups. If this sister
relationship is true it provides an astonishing reminder of how little
we know about the evolutionary history that connects living plant
groups. What kind of shared ancestor did these two lineages have
and what were the circumstances that led to one becoming aquatic
and the other a tree? The existence of such differences in sister lineages
demonstrate the potential evolutionary fluidity of morphological
characters, and emphasises the fact that living plants are only
the tips of a highly branched phylogenetic bush. Within the bush
many branches end blindly and do not reach the surface so that
intermediate linking kinds between living plant groups do not now
exist.
5.3 CLASS MAGNOLIOPSIDA – FLOWERING PLANTS 237
Figure 5.81. Fumarioideae
(Corydalis): (a) plant; (b) detail of a
single flower.
Figure 5.82. Protea: the long
slender flowers are grouped in
heads surrounded by showy
bracts. Each flower has a single
pistil surrounded by four petals
(three fused and one free) with
anthers adnate to the petals.