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Seed Plants II: Angiosperms (Changing Concepts About Early Angiosperms (In…
Seed Plants II: Angiosperms
Changing Concepts About Early Angiosperms
Concepts about the nature of early angiosperms have changed as our
knowledge of existing and fossil plants has become more complete
In the last century, wind pollinated trees
(alders, elms, oaks, & plane trees)
were grouped together in a “subclass Hamamelidae”
& were considered the most relictual living flowering plants
these species tend to be large trees w/ dense wood
their flowers are small & simple
Wind-pollinated flowers don't need to attract pollinators
they don't need to be large or colorful & they don't need petals or sepals
100 yrs ago, C. E. Bessey developed hypothesis of the ranalean flower
a Magnolia-type flower was thought to be relictual
Such a flower is generalized; meaning it has all parts
Most botanists long ago concluded angiosperms are monophyletic
Almost all recent DNA studies also indicate monophyly of angiosperms
Currently, many paleobotanists & taxonomists believe that the transition
from gymnosperm to angiosperm occurred during the Jurassic
& Lower Cretaceous Periods of the Mesozoic Era
Classification of Flowering Plants
Soon after their origin, flowering plants began to follow 2 distinct lines of evolution
& almost all angiosperms are classified as monocots or eudicots
No single character always distinguishes
a monocot from a eudicot,
some species would fool most botanists
monocots
have only one cotyledon on each embryo
their leaves usually have parallel veins
because the leaves are elongate & strap shaped
never have ordinary secondary growth and wood
Flowers have their parts arranged in groups or multiples of 3
vascular bundles are distributed throughout the stem
eudicots
Eudicots are much more diverse & include a greater number of
families, genera, & species
have 2 cotyledons & reticulate venation in the leaves
vascular bundles occur in only one ring in the stem
can be woody, herbaceous, or succulent
Flower parts occur in sets of five most often
the early angiosperms diverged into several clades
now called the basal angiosperms
Basal Angiosperms
basal angiosperms contain the living descendants of
several groups that originated while angiosperms were still a young clade
The 3 groups of extant descendants of these clades,
Amborellaceae, Nymphaeaceae, & Austrobaileyales,
haven't remained static evolutionarily & haven't preserved all ancestral features intact
Nymphaeaceae are the water lilies
small, soft-bodied herbs w/vascular bundles
scattered like those in monocots,
completely lack any wood
they have almost nothing in common w/ either gymnosperms or seed ferns
Amborellaceae
small trees in forests of New Caledonia
wood contains tracheids but no vessels
little parenchyma
dioecious
Austrobaileyales contains woody trees
w/ bisexual flowers, w/ stamens & carpels being similar to those of Amborella
Monocots
Commelinoid Monocots
The following 4 orders of monocots are known as the commelinoid monocots
they differ from the others in several unusual synapomorphies
They have unique types of epicuticular wax
Their walls have unusual types of hemicelluloses
& ultraviolet-fluorescent compounds
Their pollen contains starch, as does their endosperm
Alismatales
contains many aquatic herbs such as Sagittaria
(arrowhead)
contains many aquarium plants such as:
Hydrocharis, Najas, & Hydrilla
most often found in swamps & marshes
partly or entirely submerged
the ancestors of Alismatales were more complex & massive
& had more sclerenchyma
less highly modified, often having large leaves,
considerable amounts of fiber,
& a thick cuticle on the leaf epidermis
Asparagales
Their carpels fuse side by side starting at their bases
the fused sides being called septa
do not fuse all the way up to the style,
the open areas secrete nectar; these are septal nectaries
extremely diverse in morphology
Arecales
This order contains familiar plants, the palms, in family Arecaceae
easily recognizable by their solitary trunk
all have scattered vascular bundles
leaves of palms always occur only near the shoot apex
Poales
This order contains the grass family Poaceae
as well as cattails (Typha), bromeliads, & sedges
They also include most foods, such as
wheat, barley, oats, rye, corn, rice & sugar cane
Zingiberales
This order contains some of the most familiar of all houseplants:
Maranta, Calathea, canna lilies (Canna), & gingers (Zingiber, Hedychium)
banana (Musa) and bird-of-paradise (Strelitzia)
Almost all are tropical, & most are soft, nonleathery herbs
The leaves are broad & have a petiole
Eudicots
Basal Eudicots
Caryophyllales
Most of these families had been known to be closely related
the old group is referred to as “core Caryophyllales.”
Ex. of the core group:
cacti, iceplant, portulaca
bougainvillea, four-o’clocks, spinach, beets
Whereas other flowering plants have anthocyanin pigments in their flowers,
almost all Caryophyllales instead produce a group of
water-soluble pigments called betalains
nucellus cells proliferate and form a nutritive tissue called perisperm
Santalales
This is a small order of highly modified plants,
most of which are parasitic
The sandalwood family (Santalaceae) contains the large tree
Santalum from which sandalwood incense is obtained
Also in this family are common mistletoes,
Viscum & Phoradendron,
used as decorations at Christmas
Rosid Clade
The remaining eudicots are members of two very large,
very diverse clades, the rosids & asterids
The rosid clade (named for the rose order Rosales) consists of
many families that are so diverse w/ respect to
vegetative body, flowers, chemistry, & ecology
The rosids consist of several small orders and 2 large groups
The 2 large clades of rosids are the fabids (also called eurosids I)
& the malvids (eurosids II)
Asterid Clade
The most derived large clade of eudicots is the asterid clade
contains plants such as sunflower, periwinkle,
petunia, & morning glory
can be easily distinguished by 3 features:
They have sympetalous flowers
they always have just a few stamens,
not more than the number of petal lobes
stamens alternate with petals
many asterids have iridoid compounds,
which occur only rarely outside this group
Currently, asterids have the greatest number of species
grouped into 2 small orders
(Cornales, Ericales)
and two groups of orders
lamiids (also called euasterids I) & campanulids (euasterids II)
Many asterids are extremely important medicinally
