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

tri-foliolate leaves. Many of these families are highly resinous. The
resin is toxic and protects them to a degree from leaf-browsing animals
and also protects the wood from wood-boring insects. Azadirachta
in the Meliaceae is a source of insecticide. The Sapindaceae often have
saponins present. We are familiar with the Sapindales as the source
of fruits and seeds (litchi, longan or rambutan -- Sapindaceae; mango,
cashew, pistacia -- Anacardiaceae) and as timber trees (mahogany
Khaya, Swietenia -- Meliaceae).
5.3.8 Asterids
The Asterids are tenuinucellate. Most also have a pentamerous sympetalous
corolla, and most have an equal number of epipetalous stamens,
alternating with the five corolla lobes. This set of attributes
has long been recognized as those of a group called ‘Sympetalae’
(for a tubular corolla of connate (fused) petals). The Asterids contain
the most advanced members of the Eudicots, and the most
recently evolved. They have diversified especially in having specialised
pollination mechanisms. Floral architecture and behaviour show
many individual adaptations to particular kinds of pollinator.
Basal Asterids
cornales (dogwoods)
The Cornales exhibit a tendency, seen more fully developed elsewhere
in the euasterids, towards the possession of a pseudanthium, a compound
inflorescence of small flowers grouped together in a flat head
and made showy in different ways. In Hydrangea, for example, flowers
are in a cymose inflorescence with marginal ones sterile and showy,
and fertile central ones. An alternative pattern is seen in Cornus (Cornaceae),
which has large, showy, outer bracts like petals around the
inflorescence. Although some Cornales have a synsepalous calyx most
have free petals. There are three large families in the order, the Cornaceae,
Hydrangeaceae and Loasaceae, ranging from trees and shrubs
to robust herbs. The Loasaceae have barbed stinging hairs.
ericales (heathers)
The Ericales are a diverse order and include, as well as the heathers
(Ericaceae), other very distinct families such as the balsams (Balsaminaceae
-- fleshy herbs), the Marcgraviaceae (lianes), the Polemoniaceae
(mainly herbs, especially of arid areas, but some shrubs and
lianes), the camellias (Theaceae -- shrubs and trees with thick leaves),
and primulas (Primulaceae -- herbs). The brazil-nut family Lecythidaceae,
and the Sapotaceae, another important tropical family, are
sister families in the order. The latter produces latex and gums, and
includes species such as the chewing-gum plant Manilkara and guttapercha
plant Palaquium. One lineage of Ericales includes the insectivorous
pitcher-plant family Sarraceniaceae (Sarracenia, Darlingtonia,
Heliamphora) andRoridula with sticky resin secreting hairs (but not
insectivorous) and sensitive stamens, as well as the Actinidiaceae (the
kiwi-fruit or Chinese gooseberry).
5.3 CLASS MAGNOLIOPSIDA – FLOWERING PLANTS 245
Figure 5.104. Cornaceae:
Cornus.
Figure 5.105. Theaceae:
Camellia.
Figure 5.106. Primulaceae:
Dodecatheon.