1) Insect pollinated wind, bird, water, etc. 2) Radial symmetry bilateral symmetry 3) Perfect (both male and female parts in each flower;

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1 Week 3; Monday BRING TEXTBOOK TO CLASS Announcements: Quiz on Wednesday Arb field trip on Th 10:30 AM, Fri 10:30 AM, Sat 10:30 AM and Sat 2:30 PM; sign up in lab - directions to Arb are on class website (bus routes 43 or 48) Today we start to learn families; there will be 42 required families. Props: Magnolia flower; Laurus nobilis or Umbellularia leaves Early Angiosperm flowers. While we don t know with any certainty what the earliest angiosperm flowers looked like, we can infer from the flowers of surviving early lineages what traits they shared. Ancestral condition Derived condition 1) Insect pollinated wind, bird, water, etc. 2) Radial symmetry bilateral symmetry 3) Perfect (both male and female parts in each flower; plants hermaphroditic) unisexual (mono-,idoecious) 4) Perianth parts - sepals and petals undifferentiated distinct calyx & corolla - several to many few in set number (e.g., 3 or 5) - spirally arranged arranged in whorls - distinct (not fused to each other) fused to each other 5) Laminar stamens distinct filament & anther 6) Monocolpate pollen tricolpate pollen 7) Pistils simple pistils compound 8) Superior ovaries inferior ovaries Magnoliales and Basal Tricolpates Those families that might justifiably be called basal angiosperms are characterized by monosulcate pollen and two cotyledons. The Textbook has more information on each family; I ll just hit the highlights NOTE 1: TO USERS OF JUDD ET AL., 3 RD ED: SOME FAMILY CIRCUMSCRIPTIONS HAVE CHANGED IN 4 TH EDITION NOTE 2: WE DON T COVER THE FAMILIES IN THE SAME ORDER AS THE TEXT Page 23

2 Magnoliales Magnoliaceae (2 gen/220 spp) Magnolia family 1) woody trees or shrubs; may be evergreen or deciduous 2) ethereal (aromatic) oils primitive smell when leaves are crushed 3) simple leaves with pinnate venation and entire margin 4) large showy flowers DEMO Magnolia flower - always bisexual - many parts, spirally arranged; borne on elongate receptacle - sepals and petals poorly differentiated - laminar stamens poorly differentiated into anther and filament - ovary superior - fruit usually a follicle (often many aggregated together) or samara - follicle - 1-carpellate fruit that dehisces on one side (Magnolia sensu lato) - samara - 1-carpellate winged, indehiscent fruit (Liriodendron) - floral formula: *,,, follicle, samara Floral Formulas - shorthand notation to describe the structure of a flower X or *, Ca, Co, A, G, fruit type Rose: * 5, 5,,, aggregate achene specifically rose hip tomato: * 5,5,5,2 berry Laurales - another group of primitive woody dicots Lauraceae - most well-known family of Laurales (very diverse in tropics) (50 gen/2500 spp) Laurel family -- FAMILY NOT COVERED IN LECTURE known for ethereal oils DEMO Laurus leaves includes: Laurus nobilis - Bay; Cinnamomum zeylandica - cinnamon; C. camphora - camphor; Persea americana avocado; Umbellularia californica California bay Laurel Page 24

3 Basal Tricolpates ( basal eudicots ) these plants have tricolpate pollen, thereby placing them firmly with the other higher dicots we call Tricolpates (or Eudicots) Ranunculaceae (47 gen/2000 spp) Buttercup family This family is difficult to characterize, because of tremendous variation, but there usually is little difficulty recognizing it because of a combination of characters 1) usually herbs; some vines or shrubs 2) leaves usually simple; sometimes deeply lobed or compound 3) flowers highly variable - usually hermaphroditic (with bisexual flowers), some dioecious (with unisexual flowers) - usually radially symmetrical, - sometimes bilaterally symmetrical - parts spirally arranged or in whorls (then in 5s) - petals and sepals both showy or petals reduced/missing; petals often with nectary - ovary always superior - Stamens numerous, spirally arranged - carpels usually numerous and separate, but sometimes only one - fruit a follicle, achene, or berry - berry - 1 or more carpels, fleshy - achene - 1-carpellate indehiscent fruit floral formula: *(X) 5(- ), 5(- ), 5(- ), 5(1- ) follicle, achenes, berry Berberidaceae (15 gen/650 spp) Barberry family 1) perennial herbs or shrubs (secondarily woody) 2) lvs. simple or compound 3) fl parts in whorls of 3, or occasionally in 4 - sepals and petals usually 6 each and similar - stamens usually 6 (but may be 4 or many) with valvate anthers flaps on anthers flip up when mature to release pollen sensitive area in filament near base causes stamen to move toward gynoecium - single carpel; stigma often with 3 lobes (sometimes interpreted as a 3 fused carpels); parietal or basal placentation; - fruit usually a berry; sometimes a follicle. floral formula: * 6, 6, 4-18, 1 (3) berry, follicle [carpels fused] Page 25

4 Week 3; Wednesday Props: lvs of Betula or Corylus; Quercus inflorescences; Alnus seedling w/ nodules Rosidae sensu lato This large group includes a great amount of variety, including two prominent families of north-temperate wind-pollinated trees. Wind-Pollination Syndrome (syndrome: group of independent traits affected by same selective agent) 1) flowers appear before leaves are out 2) flowers often in catkins Catkin elongate, often dangling inflorescence of unisexual flowers typical of many wind-pollinated trees. Also called ament hence the old term Amentiferae (latin: ament - bearing) for wind-pollinated plants bearing catkins. 3) Plants often with separate staminate and pistillate flowers (plants monoecious or dioecious) this permits a greater investment in male function than would be possible in hermaphroditic flowers. 4) large number of flowers (especially males) 5) Big stamens produce lots of pollen 6) Stigmas large and plumose or roughened (papillate) to catch pollen 7) Ratio of pollen to ovules VERY HIGH (up to 6,000 to 1) 8) individual flowers small and inconspicuous - without parts for attraction 9) Flowers without scents or rewards (to attract pollinators) Fagales clade of wind pollinated trees - OVERHEAD Betulaceae (6 gen/157 spp) Birch family 1) trees or shrubs - mostly north temperate - Alders (Alnus) with N-fixing nodules on roots that house Frankia bacteria 2) Leaves simple, alternate, usually with doubly serrate margins 3) Flowers unisexual; plants monoecious DEMO lvs of Betula, Corylus - flowers subtended by bracts (1 main bract subtends the inflorescence with typically 2 bracteoles subtending each flower - flowers of both sexes usually in catkins (sometimes males only e.g., Corylus) - tepals 1-4, sometimes lacking and always very reduced - stamens ovary inferior; carpels 2 fused 4) fruit: nut (animal dispersed), samara (wind dispersed), or achene nut: hard, dry, indehiscent, usually with a single seed --> [Take a moment to catch up on fruit types: follicle, samara, berry, achene] floral formula: male * Te 0 or 4, A 4, G 0 (Te = tepals) female * Te 0 or 4, A 0, G 2 nut, samara, or achene [carpels fused] Page 26

5 Fagaceae (9 gen/900 spp) Oak family 1) trees or shrubs - mostly northern hemisphere, temperate to subtropical 2) leaves simple, alternate 3) Flowers unisexual; plants monoecious DEMO Quercus branch w/ catkins - tepals usually 6; always very reduced - male flowers in catkins; 4-40 stamens per flower - female flowers solitary, or clustered in leaf axils, or at base of catkin (e.g., Castanea, Lithocarpus); carpels typically 3 (-6), connate; surrounded by an involucre of many overlapping bracts; this structure is often described as a cupule (as in text). - ovary inferior - of 3 fused carpels, each with 2 ovules; Quercus - all but one ovule aborts; Fagus, Castanea one ovule per carpel aborts. 4) Fruit: nut (animal dispersed) Floral formula: male * Te 6, A 4-40, G 0 female * Te 6, A 0, G 3 (-6) nut [carpels fused] Show slides of birches and Oaks and read from Aldo Leopold: Bur Oak Page 27

6 Week 3; Friday Lecture: Plant Breeding Systems An essay by Joseph Wood Krutch: The Moth and the Candle (p.79 essay on yuccas and yucca moths) not enough time to read this in future Plants are incapable of reproductive behavior in the sense that animals behave to find and select mates. However, they have evolved a much greater array of reproductive systems than animals due to the fact that - most flowering plants are bisexual - sexual expression can vary over time and space - plants rely on intermediary agents to transfer pollen (containing the sperm) - plants have less rigidly controlled developmental systems and can reproduce vegetatively from many parts Asexual reproduction - reproduction of genetically identical individuals from a single parent plant - no analog in vertebrate animals exists for this, although it is quite common in insects (e.g., aphids), where it still involves the reproductive system (parthenogenesis) Asexual reproduction offers a competitive advantage to individuals particularly welladapted to the local environment, because all offspring will be genetically identical to their parent. Asexual reproduction can be divided into two basic mechanisms: Cloning or vegetative reproduction- starting new plants from vegetative parts of another plant - rhizomes/stolons lateral underground/aboveground shoots - tillers - lateral shoots at base of plants that produce adventitious roots - bulblets little bulbs from the base of big bulbs - bulbils formed in inflorescence where flower buds become little plants - layering - branches of woody plants that root when they contact the ground - cuttings - primarily horticultural, but willow branches root along rivers Agamospermy or Apomixis - production of seeds that are genetically identical to parents - This is not the same as self fertilization, which still involves genetic recombination Page 28

7 Two ways this can happen: 1) The embryo sac develops without meiosis, so that the egg cell is 2n and develops into a zygote just as if fertilization had happened. 2) The embryo sac aborts and a vegetative cell from the surrounding sporangial tissue in the ovule grows into an embryo - sometimes this requires pollination to stimulate this process (via hormones) - usually an individual plant will either be agamospermous or sexual, not both - agamospermous plants usually exhibit inviable pollen, which appears shrunken and malformed. Dandelion (Taraxacum officinale) is the best known example. However, genetic studies have shown dandelion populations to be genetically variable, probably from somatic mutants (ones that don t occur during the formation of gametes). Sexual reproduction - production of offspring following the fertilization of an egg by a sperm, which itself follows pollination in seed plants. Hermaphroditic and monoecious flowering plants may either: OR Cross-pollinate and cross-fertilize - prevents selfing and the expression of deleterious genes that are heterozygous in parent - reduces inbreeding depression (but allows build-up of deleterious alleles) - increases genetic exchange of material; brings favorable alleles together Self-pollinate and self-fertilize - self fertilization is called autogamy; the most extreme example of this is called cleistogamy where flowers never open and are only capable of selffertilization (as in some violets). - recombination still occurs in meiosis, followed by reassorting of the chromosomes when gametes fuse, although genetic diversity is lost over time - to self-fertilize, a plant must be self-compatible (SC) pollen from same plant can germinate, grow, and ultimately deliver sperm to egg of same plant - selfing can insure seed set, if no neighbors or pollinators are available - selective advantage to selfing - transmits both sets of genes to offspring - selective disadvantage to selfing - increases inbreeding depression (most severe in outcrossers that self infrequently) the advantage of selfing (2X number of genes to offspring) must be offset by a cost of inbreeding depression of at least 50%, in order to favor outcrossing. Page 29

8 Strategies to prevent self-pollination. Plants have evolved many ways to discourage self-pollination or to prevent it entirely. Self-incompatibility (SI) - a biochemical reaction in the stigma, style, or (rarely) ovary rejects self pollen and prevents pollen tube growth or entry into the ovule. Ancestral angiosperms were self-compatible and SI has evolved many times, but this has reversed itself in evolution many times, too. Unisexual flowers: Dioecy and Monoecy, prohibits or inhibits selfing, respectively Physical separation of stamens and stigma - many ways that flowers separate the anthers from the stigma - most elaborate are heteromorphic flowers (called distyly or tristyly), which have long filaments and short styles on some flowers and short filaments and long styles on others. Darwin studied distyly in Primula and predicted the presence of a third floral form in Eichhornia Temporal separation of stamen and stigma maturation (Dichogamy) Protandry - anthers dehisce and release pollen before stigma is receptive Protogyny - stigma is receptive to pollen before anthers mature Geitonogamy: self-pollination between different flowers on same plant - Many plants prevent self-pollination within the same flower by physically separating the anthers and stigmas or by having one organ mature before the other. However, these plants may still exhibit some self-pollination due to the behavior of pollinators that visit many flowers on the same plant We often can tell by looking at the flowers whether a plant is a selfer or outcrosser. Selfers small flowers nectaries absent repro. parts mature at same time all fruits mature low pollen/ovule ratio Also, remember that Selfers must be self-compatible (SC) Outcrossers large showy fls nectaries present (if animal pollinated) reproductive parts mature at different times typically only some fruits mature high pollen/ovule ratio Outcrossers may be either self-incompatible or self-compatible (SI or SC) Page 30

9 Evolutionary trends go both ways: SI SC outcrossing inbreeding A series of controlled experiments in a greenhouse or growth chamber can distinguish between these means of reproduction: Experiment #1: Grow plants in an insect-free environment (also free from any other vector) 1A - seed is set - could be agamospermy or autogamy Experiment #2: emasculate (remove stamens before they dehisce) 2A - seed set --> agamospermy 2B - no seed --> autogamy 1B - no seed is set - must be sexual, but could be SC or SI Experiment #3: artificial self pollination 3A - seed set --> self compatible 3B - no seed --> could be self incompatible or sterile Experiment #4: artificial cross pollination 4A - seed set --> self incompatible 4B - no seed --> sterile (hybrid?; X-incompatible genotypes?) Page 31