Biol3180 - Lecture 25

Front 1

what are the oldest groups of flowering plants?

Back 1

New Caledonian taxon Amborella trichopoda, the Nymphaeales (water lilies) and Austrobaileyales (Illiciaceae, Schisandraceae, Trimeniaceae and Austrobaileyaceae). Their origins predate the establishment of monocotyledons, eumagnoliids and eudicotyledons.

Amborella (or Amborella plus Nymphaeales) is sister to all other angiosperms, and hence is one of the most ancient lineages of flowering plants.

Front 2

what changes were required to go from spore-formers to seed-formers?

Back 2

1. Change from functional heterospory --> true heterospory + retention gametophyte generation

2. Replacement of sporangia (strobili/sori) with seed
- reduction of megaspore/megasporangium to one functional unit
- retention of megaspore within megasporangium

3. Enclose the reduced megasporangium a cupule-like structure formed from integuments

4. Ovule bearing leaves (Archeacycas) oriented to receive microspores

5. Learn to use sperm in processes other than fertilization (Ephedra)

Front 3

what changes were required to go from gymnosperms to angiosperms?

Back 3

sporangium on sporophyllous leaves to stamens and carpels (ovary enclosed ovules)

Front 4

when did the process of evolution from gymnosperms to angiosperms begin?

Back 4

mid-paleozoic and culminated in cretaceous (oldest fossils are from this time period)

angiosperm evolution and dispersion is closely tied with pangea and the subsequent continental movements

Front 5

what are adaptive traits of angiosperms?

Back 5

1. Tough leaves resistant to drought and cold.

2. Vessel members - efficient water-conducting cells

3. Tough, resistant seed coat

4. Precise systems of pollination and seed dispersal

5. Deciduous - enables plant to survive times when water is not available, especially important in cold climates

6. Enormous chemical diversity provides protection from herbivores

7. Evolution of herbaceous perennials and annuals that can survive in more severe habitats than woody plants.

Front 6

what factors make angiosperms so distinct/special?

Back 6

1. Ovules enclosed within an ovary (angiospermous = closed carpels)

2. Double fertilization - fusion of egg + sperm; use of sperm + polar nuclei

3. Endosperm formation - development of polyploid tissue from use of sperm + polar nuclei

4. Lack of free nuclear divisions during embryogenesis

5. Use of insect and animal vectors for pollination

Front 7

what is the major reproductive innovation of angiosperms?

Back 7

the presence of the fully enclosed carpel and pollination at the stigma

Front 8

what is the main trend of stamen development in angiosperms?

Back 8

Stamens could have evolved from (1) a leaf-like structure; (2) slender branch systems bearing terminal sporangia

Main trend of evolution in the stamens of angiosperms, from the most primitive, broad, leaf-life type to the more advanced typical-looking, anther-filament type.

Front 9

what is the evolutionary origin of sepals?

Back 9

probably derived directly from leaves

Front 10

what is the evolutionary origins of petals?

Back 10

possibly from leaves in some groups, probably derived from stamens in most groups

Front 11

what is a secondary important reproductive adaptation of angiosperms?

Back 11

the reduction of the megagametophyte to only a few cells, with double fertilization, producing the zygote, and endosperm (nutritive tissue for the seed)

Front 12

what are the characteristics of polygonum-type female gametophytes of angiosperms?

Back 12

In the overwhelming majority of angiosperms, the female gametophyte contains 7 cells and 8 genetically identical nuclei at maturity – referred to as the 'Polygonum-type‘.

At the micropylar pole, a three-celled egg apparatus contains the egg cell and two sterile accessory cells, the synergids.

The large central cell, which is the target of the unique angiosperm second fertilization event, is binucleate, and as a consequence, endosperm derived from a Polygonum-type female gametophyte is triploid.

At the chalazal pole are three sterile cells, the antipodals.

This polygonum-type anatomy appears in ancient angiosperm lineages

Front 13

what are the three major angiosperm female gametophytes?

Back 13

Nuphar/Schisandra Type: 1 module, four nuclei distributed in the egg, two sterile cells, and the central cell

Polygonum Type and Amborella Type: both have 2 modules, mitosis leads to eight nuclei distributed among seven cells, including a central cell with two nuclei.

Front 14

aside from their origin, what is one of the biggest questions regarding angiosperm origin?

Back 14

the nature of their original anatomy: originally woody trees/shrubs, or were they herbs?

Front 15

what are the two competing theories of the first angiosperm plant body types?

Back 15

The Woody Magnoliid Hypothesis -- suggests that the basal lineages were small trees with slower lifecycles

and

The Paleoherb Hypothesis -- suggests that the basal lineages were herbs with rapid lifecycles

Front 16

what are the primary tenets of the wood magnoliid hypothesis?

Back 16

- favors an early angiosperm with morphology similar to living members of the Magnoliales and Laurales

- The carpels are imperfectly fused, and make a physical intermediate between a folded leaf and fused pistil

- The flower was NOT the key innovation for the rapid diversification of angiosperms; in fact woody magnoliids are not particularly diverse, even today

- favored by molecular studies

Front 17

what are the primary tenets of the paleoherb hypothesis?

Back 17

- suggests that the basal lineages were herbs with rapid lifecycles

- Basal angiosperms are tropical paleoherbs, plants with uncomplicated flowers and a mix of monocot and dicot features.

- Key innovations of flowers and a rapid life cycle were present in the earliest angiosperms.

- It has been suggested that changes in climate or geography provided opportunities for these early angiosperms to diversify.

Front 18

what have been the general evolutionary trends from earlier to extant flowers?

Back 18

1. flowers with many indefinite parts to few parts that are definite in number

2. floral parts that were separate to parts that are fused

3. ovary has gone from being superior to inferior

4. earlier flowers are radially symmetrical becoming bilaterally symmetrical in later flowers

5. Floral axis becomes shortened with a less evident spiral arrangement of the carpels

6. Development of distinct perianth whorls; separate calyx and corolla

7. Later we see the number of floral whorls becomes reduced (from 4 in early flowers to 3, 2, 1 in more advanced forms)