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Origins of Angiosperms
Spring 2010
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Outline Origin of the angiosperms Characters of angiosperms
Brief history of angiosperm classification Major groups of angiosperms ANITA grade
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Origin of the Angiosperms
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? Divergence estimated at ca. 325 mybp Conifers Ginkgo Gnetophytes
Cycads Ginkgo Conifers Gnetophytes Angiosperms ? Progymnosperms (“seed ferns”) Divergence estimated at ca. 325 mybp
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Geologic Time
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Timing of Angiosperm Divergences
The timing of the origin of the angiosperms still is uncertain, but most would agree on a Triassic or Jurassic initial divergence, although there is no unequivocal fossil evidence A demonstrable “burst” of phylogenetic radiation is found in the fossil record beginning in the mid- to-late Cretaceous, mybp
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Figure 7.16 from the text
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Origin of the Angiosperms
pollen grains from ca. 140 mya (early Cretaceous) but already major radiation! earliest flowers 130 mya likely no extant group of seed plants is very closely related to the angiosperms!
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Origin of Angiosperms Cycad-like plants: Bennettitales?
large, flowerlike strobili: pollen-producing organs surrounding an axis bearing naked ovules/seeds
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Origin of Angiosperms Modification of a “seed fern” such as Caytonia?
fossil: ovule
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Origin of Angiosperms Archaefructus ca. 130 mya
ancestral flowering plant or extinct off-shoot of an extinct lineage? aquatic plant (dissected leaves) elongate reproductive axes: -paired stamens below -several-seeded carpels above
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Characters of Angiosperms
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Reduced male and female gametophytes!
Angiosperms (Flowering Plants) “Dicotyledons” Magnoliids Eudicots Monocots -- likely evolved WITHIN angiosperms Reduced male and female gametophytes! ALSO: -- nonmotile sperm! (evolved independently in certain non flowering taxa)
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What makes a plant an angiosperm?
Flower (usually with perianth) Carpels with a stigmatic surface for pollen germination; ovules enclosed within carpels; fruit Ovules with two integuments Reduced female gametophyte, usually 8 nuclei in 7 cells – no archegonium Double fertilization with the production of 3N endosperm Stamens with two pairs of lateral pollen sacs (microsporangia) Xylem – most with vessels (evolved within angiosperms) Phloem – sieve tube members with 1 or more companion cells derived from the same mother cell
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Figure 4.16 from the text Flower
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Spiral undifferentiated
perianth parts = tepals (plesiomorphic)
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Differentiated sepals and
petals (each in whorls) (apomorphic)
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Laminar stamens in basal angiosperms paired pollen sacs connective microsporangium filament
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Early carpel with stigmatic crest… Figure 4.19 from the text Figure 4.20 from the text …to the derived carpel with a style and an apical stigma.
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Female gametophyte in angiosperms
-no waiting time as in gymnosperms! -note 2 integuments (bitegmic; some angiosperm lineages have lost one integument) -gymnosperms have only 1 integument (unitegmic) mature ovule ovule
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Seed development in angiosperms
-no waiting time as in gymnosperms! double fertilization seed
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flower fruit Avocado (Persea, Lauraceae) exocarp mesocarp endocarp
seed
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Vessels in Angiosperms
are the water (solute) conducting cells of the xylem in most angiosperms ends of cells have openings (perforation plate), cells shorter and wider more efficient, faster rate of flow but more susceptible to air bubbles (embolisms) than tracheids are may have arisen independently in two or more angiosperm lineages but may have had a single origin
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Origin of vessels from tracheids
Figure 4.32 from the text
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Angiosperm phloem sieve tube members + companion cells
stm = specialized sugar-conducting cells of the phloem of angiosperms; lack a nucleus at functional maturity cc = parenchyma cells associated with stm -function to load/unload sugars into stm cavity -derived from the same mother cell as its stm stm
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Brief history of angiosperm classification
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Alternative ways of thinking about early angiosperm characters…
“Old” School (German) - Engler - “Simple is primitive” (Few floral parts) - Ancestors are conifers - Pollination by wind - Modern relicts = “Amentiferae” (catkins) “New” School (American) – Bessey - “Flowers with many parts are primitive” - Ancestors are Cycad-like plants - Pollination by primitive insects - Modern relicts = Magnolias and allies
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Heinrich Gustav Adolph Engler (1844-1930)
German Botanist at Berlin Botanical Garden -Was the primary European in interpreting the grouping of major angiosperm assemblages -“Few simple flower parts primitive” -Small, unisexual flowers primitive
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Englerian ‘Primitive Taxa’
Juglans sp. Quercus sp. “Amentiferae” Betula sp.
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Charles Edwin Bessey (1845-1915)
-Botanist at Iowa State University from (left in 1884 to teach in Nebraska) -Was a “major player” in interpreting and understanding angiosperm evolution -“Many flower parts primitive” Bessey Hall Iowa State University
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Bessey’s “Cactus” Placed plant groups with many floral
(1915) Placed plant groups with many floral parts in a basal position as the ‘ancestral’ forms. Outlined ‘dicta’ for the construction of phylogenies using the evolutionary trends in character changes. Polypetalous flowers, insect pollination, cycad-like ancestors
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Besseyan ‘Primitive Taxa’
Nymphaeaceae Magnoliaceae
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Figure 7.16 from the text
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Major Groups of Angiosperms
Basal Angiosperms (ANITA grade) - Amborellaceae - Nympheaceae - Illiciaceae Magnoliid Complex (incl. “paleoherbs”) - Magnoliales - Piperales - Winterales MONOCOTS EUDICOTS (tricolpates)
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Major Groups of Eudicots
Basal Tricolpates - Ranunculales and allied families Caryophyllales & Saxifragales Rosid Clade - Basal Rosids - Eurosids I (Fabids) - Eurosids II (Malvids) Asterid Clade - Basal Asterids - Euasterids I (Lamiids) - Euasterids II (Campanulids)
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ANITA grade Amborella (Amborellales) Nymphaea (Nymphaeales)
Illicium (Austrobaileyales) Trimenia (Austrobaileyales) Austrobaileya (Austrobaileyales)
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Figure 9.1 from the text > 125 mybp > 140 mybp ANITA grade
Grade = a polyphyletic (or paraphyletic) group whose members share a similar level of morphological or physiological complexity. > 140 mybp
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Major Angiosperm Clades
Amborellaceae Nymphaeales Austrobaileyales MAGNOLIID COMPLEX MONOCOTS EUDICOTS [TRICOLPATES] “BASAL FAMILIES” Soltis et al. 2000, APG II 2002, Judd et al. 2002
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Basal Angiosperms: Amborellaceae
New Caledonia Understory shrub; plants dioecious 1 species (monotypic): Amborella trichopoda Leaves simple, evergreen Flowers small, unisexual: ♀ apocarpous, with stigmatic crests; ♂ with laminar stamens Significant features: Most basal of all flowering plants; no vessels in wood Special uses: (none)
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Basal Angiosperms: Amborellaceae (Amborella Family)
Amborella trichopoda
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Basal Angiosperms: Nymphaeaceae (Water Lily Family)
Widespread, tropics to temperate regions Aquatic rhizomatous herbs, sap milky 70 species; 8 genera Flowers: many parts; laminar stamens; “floating”; colorful perianth; “beetle” syndrome Special uses: ornamentals; sacred lotus Required taxa: Nymphaea (water lily)
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Basal Angiosperms: Nymphaeaceae (Water-lily Family)
numerous petals, stamens, carpels laminar stamens pollen monosulcate stigma discoid, radiating berry-like fruit, dehiscent perisperm usually lack vessels (or have tracheid-like vessels)
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Nymphaea odorata – Water Lily
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Nymphaea tuberosa Water Lily
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Nuphar Water Lily
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Victoria amazonica – Giant Water Lily
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Basal Angiosperms: Illiciaceae (Star Anise Family)
SE Asia, SE USA and Caribbean Trees and shrubs 1 genus, Illicium; ca. 40 species Flowers: many floral parts/tepals; 1 ovule/carpel Special uses: star anise (spice) Required taxa: (none)
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Illicium – Star Anise Illicium parviflorum Illicium floridanum
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As we venture through the various major groups of angiosperms…
Identify the plesiomorphic characteristics associated with particular groups and note their apomorphies (if any) as well. Try to associate “syndromes” of characteristics with each group (make note of special characters occurring together). One good way to study is to write keys to the groups we cover in any given unit. Names of groups are important! Learn to spell and say them! Ask questions!!
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