BIO SCI 152 1st Edition Lecture 13Flowering Plants – the AngiospermsLearning ObjectivesAfter suitable revision, you should be able to –• Recognize and explain some of the key evolutionary innovations whichmake Angiosperms so successful as a plant group • Name parts of the flower and know their role in achieving reproduction • Describe key differences between monocots and dicots • Describe the life cycle of plants and name the type used by Angiosperms • Recognize key life cycle steps in Angiosperms • Describe where you would find the gametophyte • Recognize pollination vectors and the likely characteristics of flowersthey pollinate VocabularyAngiosperm Anther SporopolleninXylem StamenGenetic diversityVessel element Pollination Selfing (self-Evolutionary Fertilization fertilization)innovation Double fertilization Out-crossingFlower Meiosis MonoecyCalyx Syngamy DioecyCorolla Zygote PollinatorPetal Endosperm Co-evolutionSepal Embryo Nectar guidesPistil Pollen tube Floral mimicryStyle Microspore Corolla tubeStigma Megaspore NectarCarpel Polar nucleiEvolution of Angiosperms• More recent than gymnosperms • Ancestors – 140 mya • Diversified rapidly in Cretaceous • Widespread by 100 mya • Outcompeted gymnosperms around 59 - 100 mya • Angio Gk. vessel/container• Sperm Gk. seed Characteristics of Angiosperms• Most numerous (successful) plant group on planet (235,000 spp) • Major evolutionary innovations of Angiosperms– Xylem – vessel elements in addition to tracheids found in conifers – Flowers - attract pollinators (Radiation of flower species accompanies by radiation in insect species)– Double fertilizationCalyx and Corolla Fig. 21.14Calyx - the sepals (usually the outer-most whorl of a flower)Corolla - the petalsThe perfect, complete flowerInflorescences – clusters of flowersComplete and incomplete flowers‘Perfect’ and ‘Imperfect’ FlowersFig. 27.1• Imperfect – missing either stamens or carpels – unisexualComplete – having all 4 organs – petals, sepals, stamens and carpelsIncomplete – missing one or more floral partse.g. Grass flowers – missing petalsImperfect flowers of cornTop – female pistilate flowersBottom - male staminate flowersMonocots and Dicots Fig 21.26Monocots vs Dicots vascular systemDicots – net veination Monocots – parallel veinationFlower form: Monocots – 3s, Dicots – 4,5sAngiosperms are Diploid DominantPlant Life Cycles SummarizedEvolutionary trend towards reduced gametophyte Fig. 21.12Angiosperm Sporophytes and gametophytesAngiosperm Life Cycle Fig. 21.25, 27.2Megaspore and MicrosporesDouble fertilization (fig. 27.4) – key innovation in angiosperms- Detailed ultrastructure visible under light or electron microscope - Resistant sporopollenin coat – survives geological time-frames - paleo-botany - Pollen tube grows 1.5 – 3 mm per hour down the styleGrowth of pollen tube down the style to deliver the sperm cells to the ovaryWhy do plants do sexual reproduction ?Genetic DiversityEnsuring gamete (pollen) exchange – cross pollinationHow do plants avoid self-fertilization?Promoting cross-pollination and prevent self-fertilization:• Monoecy and Dioecy • Timing of gamete maturity • Genetic ‘self-incompatible’ mechanisms • Flower structure related to specialized pollinators Monoecy and dioecyMonoecious – male and female flowers separate but on the same plant e.g. Zea mays (corn) (encourages outcrossing)Dioecious – male and female plants separate (must outcross!)Male vs female gametes available and ready at different times.Genetic self-incompatibility – recognizes same genes and stops pollen tube growth Fig. 27.3Angiosperm and pollinator co-evolutionIn class exercise : Which vectors pollinate which flowers?Flower characteristics:• Size • Shape • Colors • Odor/perfume • Nectar supply • Day vs night openBee pollinated flowersFlowers pollinated by mothsFlowers pollinated by butterfliesAdaptation to out-crossing :Co-evolution with specialized animal pollinators Resulting in enormous floral diversityBird-pollinated flowersBat-pollinated flowersFlowers pollinated by other mammalsWind-pollinated flowersWater dispersal of pollen boats in Ribbon weed (Vallisneria