Chapter 23: Seed Plants II: Angiosperms (Monocots (Commelinoid Monocots…
Chapter 23: Seed Plants II: Angiosperms
Embryophytes became distinct from charophyte green algae.
Since then, the flowering plant clade--the angiosperms--contains the greatest number living species--257,000.
All classified in a single division, the
(often called the Angiospermophyta).
, the edges of sporophyll primordia crowd against each other and grow shut.
Sometimes leaves a visible suture, sometimes closing so completely that no sign of a seam remains.
This is called a
It develops into a fruit that encloses the embryos as they develop into seeds.
"Angio" means "clothed"
In the transition from their ancestral group to being angiosperms, fertilization evolved.
Such that the second sperm cell of the pollen tube fuses with the polar nuclei of the megagmetophyte, producing the endosperm nucleus.
This process of
is universal in flowering plants.
Within the vegetative body, the major transitions were the evolution of vessel elements and sieve tubes.
developed reticulate venation
adaptable to a variety of functions, not just photosynthesis
Quite a few plants were considered to be basal angiosperms on the basis of having wood without vessels.
It was thought that these were
(that they lacked vessels because their ancestors lacked them).
Many other features, however, were inconsistent with the idea of these being a natural, early group.
Current hypothesis is that perhaps only
is primitively vesselless and that the others arose after vessels had originated but then these groups lost them.
If so, they are
Their tracheid-based, gymnosperm-like wood is a derived feature that looks like a primitive one and misled us for years.
Sieve tubes may have originated next.
Several species still have sieve cells in their phloem.
All gymnosperms and seed ferns are or were woody plants and so are most of the basal angiosperms and eudicots
1 more item...
Other derived features are...
Fusion of petals into one structure (
, that is, flowers that are bilaterally symmetrical, not radially symmetrical.
The fusion of the carpels into a single structure (a
Even more specialized characters such as succulence, parasitism, epiphytism, bulbs, corms, tubers, tendrils, and insect-trapping leaves.
Originated only much later, after angiosperms diversified into many clades.
These innovations present in only a few families or species.
It should not be thought that the flowering plants are now "finished," that all their evolution has already happened.
Pollen grains have either 3 germination spores (
) or have some condition derived from the tricolpate mechanism.
14 large orders with over 50,000 species
Pinnately compound leaves.
None of them have any of the highly relictual features found in basal angiosperms.
More derived than basal tricolates
Also consist of two large groups.
Contain more than 100 families; difficult to find universal characters
Consist of several small orders
One small order: Geraniales, contains the geranium family, Geraniaceae.
One of the small orders: Vitales contains Vitaceae, the grape family.
Consists of many families that, taken as a whole, are so diverse with respect to vegetative body, flowers, chemistry, and ecology
Those of the second group share different features with a third group and so on.
Leads to a distinguishable, larger picture of phylogenetic relationships
Some share enough characters with others to indicate a relationship
Makes it difficult to see they are all related.
Named for the rose order Rosales
Can be distinguished from other angiosperms on the basis of 3 features:
Stamens alternate with petals.
Always have just a few stamens, not more than the # of petal lobes.
Even its most basal members were much more highly derived than plants in the basal angiosperms.
A sister to clade of rosids, originated perhaps as recently as 60 million years ago
Contains plants such as sunflower, periwinkle, petunia, and morning glory.
Most derived large clade
Sandalwood family (Santalaceae) contains the large tree Santalum from which sandalwood incense is obtained
A small order of highly modified plants, most of which are parasitic.
Postulated to have arisen from ancestors similar to Ranunculaceae
Nature of sieve tube plastids.
Instead, nuclleus cells proliferate and form a nutritive tissue called
which surrounds the developing embryo.
Perisperm usually absorbed almost completely by the time the seed is mature.
Endosperm develops only a little and then fails to continue growing.
Other flowering plants have
in their flowers, almost all Caryophyllales instead produce a group of water-soluble pigments called
carnations and chickweeds
spinach, beets, and Russian thistle
Ex: Plantanaceae, sycamores (aka plane trees)
Flowers mature into spherical clusters of hundreds of tiny dry fruits
Have small, inconspicuous clusters of flowers in the spring
Usually in dangling inflorescences containing many staminate flowers and just a few carpellate flowers.
Large trees with reduced wind-pollinated flowers
Poppy family, Papaveraceae
Numerous ornamental species
Argemone (pickly poppy)
Ranunculales and several others are believed to be clades that diverged at early stages in eudicot evolution.
Flowers have so little fusion of parts
Each has usually many stamens and carpels
Stamens remain free or may fuse together in a tube or fuse to carpels.
All remain separate of others
Changing Concepts About Early Angiosperms
Early angiosperm concepts change as our knowledge of existing and fossil plants has become more complete.
In last century, wind-pollinated trees (alders, elms, oaks, and plane trees) were grouped in "subclass Hamamelidae."
Considered most relictual living flowering plants.
These species tend to be large trees with dense wood.
Flowers small and simple.
Usually without sepals and petals.
Many gymnosperms have similar features.
HOWEVER, could NOT be relictual because wood contains...
features not found in gymnosperms
Simple through specialization and reduction:
Wind-pollinated flowers do not need to attract pollinators.
They do not need to be large or colorful-they do not need petals or sepals.
Recent DNA studies
Indicate that syndrome of large, wind-pollinated trees is a derived condition within angiosperms
1 more item...
Approximately 100 years ago
C.E. Bessey developed hypothesis of
-type flower was thought to be relictual.
Such a flower is
That is, has all parts (sepals, petals, stamens, and carpels)
And arranged spirally
Carpels occur in a superior position, above the other parts
Easy to postulate evolution of all various existing flower types from a ranalean, generalized ancestor.
4 more items...
Most botanists long ago concluded that angiosperms are monophyletic.
Complex features probably did not evolve more than once.
Almost all recent DNA studies indicate monophyly of angiosperms.
Gymnosperms of Jurassic and Triassic Periods
Focus on centering on cycadophytes and glossopterids.
Much of the various groups have begun to develop angiosperm-like features.
The perianth usually consists of 3 outer and 3 inner members.
Look so similar that instead of referring to as sepals and petals, known as
Gynoecia of many monocots composed of several carpels (usually 3)
Either free of each other or at most only slightly fused together.
Ancestors probably herbs with either no vascular cambium or little cambial activity.
All lack ordinary secondary growth and wood.
Widely believed to have arisen from early angiosperms approx. 80 to 100 million, perhaps even 120 million years ago.
Leaves broad, and have a petiole.
Plants grow in heavy shade of jungle understory where light interception is important.
Almost all tropical, most soft, non-leathery herbs.
Approx. 1,000 species
Many flowers have derived features
Typically consists of 3 carpels that have fused almost completely.
Inferior, located below the sepals and petals
Same is often true of the petals
Forming a tube
Adjacent sepals are often fused to each other
Tend to have large, showy flowers pollinated by insects, birds, or bats.
Contains familiar houseplants
In warmer southern states, banana (
) and bird-of-paradise (
, canna lilies (
), and gingers (
Often tinged with red
Usually much branched, with a line of pubescence or glabrous
Sometimes rooting at the nodes and often forming mats, or ascending or straggling
Shoots prostrate to decumbent
Roots thick, fibrous
Grasses abundant in flat, open, and dry regions in the central areas of all continents.
Accounts for one quarter of all vegetated land on Earth.
Main sources of meat--cow, pig, and sheep--raised on grassland and fed corn.
50% of all calories consumed come from grass seeds
Include most food like wheat, barley, oats, rye, corn, rice, bamboo, and sugar cane.
Contains about 8,000 species
Contains the grass family Poaceae, cattails (
), bromeliads, and sedges.
Simple leaves, after fully expanded torn by wind
Or palmate ones (fan palms)
Either into a pinnate pattern (feather palms)
Leaves occur near the shoot apex
Never distributed along the length of the stem.
All have scattered vascular bundles
Varies from 1.0 m wide in some and only 1.0 cm in others.
About 3,500 species, all of which are easily recognizable by their solitary trunk
Contains familiar palms, in family Arecaceae
Differ from others in several unusual synapomorphies.
Unique types of epicuticular wax.
Multiple studies of
, and other DNA regions support this as a distinct clade.
Walls unusual types of hemicelluloses
Pollen contains starch, as does their endosperm
Classification of Flowering Plants
In the 1980s and 1990s, the most widely used monograph of the entire division was
An Integrated System of Classification of Flowering Plants
By Dr. Arthur Cronquist of the New York Botanical Garden
Since then, cladistic studies involving DNA, biochemistry, and anatomy often proposed phylogenies that agreed well with those of Dr. Cronquist for certain clades but disagreed with others.
Two widely used reference books are...
Plant Systematics, A Phylogenetic Approach
(3rd Edition) by W.S. Judd et al.
by Michael Simpson
Angiosperm Phylogeny Group (APG), which is a semi-informal collaboration of many systematists
Classifications on www.mobot.org/MOBOT/research/APweb/
Soon after origin, flowering plants began to follow two distinct lines of evolution.
Monocot/eudicot divergence did not occur right away,
Instead, the early angiosperms diverged into several clades now called the
Nymphaeales (water lilies) have many features of monocots, but classifying them as monocots create a polyphyletic group.
greatly resemble eudicots.
Cannot be classified with eudicot clade
Cannot construct a group that includes some descendants of a common ancestor but excludes others.
The common ancestor that includes both them and the eudicots also includes monocots.
Many different DNA sequences indicate they had become reproductively separate from the other angiosperms very early.
Classified as monocots or dicots before
Not newly discovered
: informal term for any member of the flowering plant class Liliopsida
Ex: lily, iris, palm, agave
: the clade of angiosperms that contains most species formerly known as dicots
Contain living descendants of several groups that originated while angiosperms were still a young clade.
Ancestors became reproductively isolated before distinctive angiosperm traits had originated.
Other magnoliids are laurels and avocado (Laurales) and peppers and peperomias (Piperales).
Ex: Family Magnoliaceae contains trees with wood similar to that of gymnosperms in that it lacks vessels, fibers, and axial parenchyma.
Pollen grains have only a single germination pore.
Eudicots have 3 germination pores.
, as are all other basal angiosperms and monocots.
Carpels not fused together into a pistil as occurs in almost all monocots and eudicots.
flowers have numerous stamens and carpels arranged in spirals
Ancestors diverged from early ancestors than clades above.
Morphologically, the magnoliids do not differ greatly from these two earlier clades
Based on DNA evidence
3 groups of extant descendants of these clades:
Have not remained static evolutionarily and have not perserved all ancestral features.
Others carpellate flowers
Have interlocking, secretory hairs that act as stigma
Have 5 or 6 carpels whose edges do not seal tightly
Flowers are small with 5 or 11 tepals
Some plants have staminate flowers
Have numerous stamens
Wood has no vessels and little parenchyma
Wood contains tracheids
Very different, being small trees in forests of New Caledonia
Only one species in clade
in so many features, cannot resemble the earliest angiosperms
Instead, one or the other--or all three--have undergone considerable evolutionary change since their clades originated.
Contains woody trees with bisexual flowers
Stamens and carpels similar to
Almost nothing in common with either gymnosperms or seed ferns
Pollinated by animals
Large colorful flowers
Exposure to any conditions on land result in death
Vascular bundles scattered
Stems must be submerged underwater
Small, soft-bodied herbs
Lack any wood