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

228 ORDERING THE PATHS OF DIVERSITY
(a)
(b)
Figure 5.58. Nymphaeales: (a)
Nymphaea; (b) Cabomba.
Figure 5.59. Schisandra.
nymphaeales (water-lilies)
The next most-basal flowering plants are either six genera and about
40 species of water-lilies, with large flattened floating leaves and large
bowl-shaped flowers in the Nymphaeaceae, or two genera (Brasenia
and Cabomba) of waterweeds with floating stems and relatively small
simple and unspecialised flowers in the Cabombaceae (Figure 5.58).
The Nymphaeales have a mixture of unspecialised, probably primitive
features, and specialised features such as abundant aerenchyma
tissue, adapting them to their aquatic habitat. Vessel elements have
been recorded in some species but these are not like those of other
flowering-plants. The pollen has a tectum of sorts but its inner layer,
the endexine, is compact and lacks the columellate appearance of all
other flowering-plants. Some features are shared with the monocots:
the primary root is soon aborted and the stem has scattered closed
bundles. The showy petals have originated as sterile stamens (staminodes).
The families differ in the degree of fusion of the carpels; laterally
fused in Nymphaeaceae and free in Cabombaceae. Flowers are
normally hermaphrodite with only a weak distinction between sepals
and petals. Sepals and petals are arranged in a spiral. The largeflowered
water-lilies Nymphaea, Victoria and Nuphar are specialised for
beetle pollination. It is remarkable that similar looking aquatic plants
have evolved convergently in the distantly related Nelumbo (Proteales)
and Nymphoides (Asterales).
schisandrales (including illiciales and
austrobaileyales)
The Schisandrales include four families of small trees and scrambling
shrubs or lianes. austrobaileyaceae: These are lianes. Austrobaileya
scandens, one of only two species in this family, grows in
NE Australia, and has flowers that smell of rotting fish. The flowers
have 12 perianth segments, 6--11 laminar stamens, with sterile stamens
(staminodes) inside surrounding the 6--9 free carpels. trimeniaceae:
There are only two genera, Trimenia and Piptocalyx, with a
total of five species, of small trees and scrambling shrubs found from
SE Asia to Australia. They are monoecious with small wind-pollinated
flowers. The female flower has a single carpel and the male flower
6--25 stamens in pairs. illiciaceae: There is only one genus, Illicium,
with 42 species of trees and shrubs found in SE Asia and USA,
Mexico and the Caribbean. Flowers may have 12 or more perianth
segments, and 7--15 carpels. Illicium has peppery tasting leaves, and
produces a star-shaped unripe fruit called star-anise that is used as a
spice. schisandraceae: There are only two genera, Schisandra and
Kadsura, and a total of 47 species of lianes and twining shrubs, found
in East Asia and eastern North America. The Illiciaceae and Schisandraceae
share some chemical features, a primary vascular cylinder
and tricolpate pollen. Unlike the previous two orders some members
have clearly formed vessel elements although of a primitive sort, with
sclariform (ladder-like) perforations.