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

244 ORDERING THE PATHS OF DIVERSITY
(a)
(b)
Figure 5.101. Brassicaceae:
(a) half flower; (b) floral diagram.
Figure 5.102. Malvaceae:
Hibiscus.
Figure 5.103. Anarcardiaceae:
Pistacia.
by scales and have a minute perianth. The strange she-oak (Casuarina)
of South-East Asia and Australia was once considered to be very primitive
because of its very simple inflorescence. The flower consists only
of a bract with two scale-like bracteoles with, in the male, a single
stamen and, in the female, a single pistil. Male flowers are aggregated
into catkins and the hard bracteoles of the female flowers form part
of a woody ‘cone’.
Eurosid II
The Eurosid II clade includes these important orders: Brassicales,
Malvales, and Sapindales.
brassicales (crucifers)
The Brassicales include sister lineages so distinct and without intermediates
that one wouldn’t guess their close relationship. The families
Brassicaceae (crucifers), Resedaceae (mignonette), Limnanthaceae
(poached-egg flower), Batidaceae (saltwort), Koeberliniaceae (allthorn),
Setchellanthaceae, Moringaceae (Bennut), Caricaceae (papaya) and
Tropaeolaceae (nasturtium) are very distinct in their floral morphology.
For example, the Brassicaceae is also called the Cruciferae because
of its cross-shaped flowers of four petals and usually six stamens. In
contrast the Resedaceae usually has six fringed petals and the Tropaeolaceae
has five and also has a long hairy claw. One floral feature that
is present in several families of the order is a nectariferous portion
of the axis below the stamens (androgynophore) or pistil (gynophore).
One of the most significant features these families share is the possession
of mustard oils (glucosinolates). This seemingly obscure chemical
character provides protection against herbivory and fungal attack.
Another interesting feature is the usual lack of mycorrhizae in the
Brassicaceae, perhaps because they tend to occupy relatively nutrient
rich early successional situations.
malvales (hibiscus and mallows)
The Malvales are linked by a chemical characteristic of obscure significance,
the presence of mucilage cells, or canals and cavities. The
Malvales include the important family of tropical trees, the Dipterocarpaceae.
Many exhibit a common rosid trait of showy polypetalous
flowers with many stamens. The sequence in which the stamens
mature is centrifugal, a pattern of development that was thought
to be significant enough to warrant separating them from the rosids
(centripetal development) in a group called the Dillenidae, but this
pattern of development is difficult to see in the Malvaceae where the
stamens are united to form a tube around the style.
sapindales (mahoganies)
The Sapindales also include several very important tropical and subtropical
families of trees and shrubs such as the Meliaceae (∼575
species), Sapindaceae (∼1350 species), Anacardiaceae (∼850 species)
and Burseraceae (∼540 species). They frequently have pinnate or