The Flower - What is it

Magnoliophyta - Flowering Plants Introduction to Angiosperms The Flower What is it? • Latin base for "angio-" or vessel; so "angiosperm" means "vessel for the seed" or those seed plants with the seed encased in an ovary • Angiosperms are the dominant group of land plants today and arose about 140 million years ago during the late Jurassic. • There are about 275,000 species of flowering plants. • Angiosperms reproduce faster than gymnosperms and have co-evolved in numerous ways with animal pollinators. Magnoliophyta - Flowering Plants 4 Features Define Angiosperms: 1. Possession of flowers 2. Further reduction of the gametophyte stage embryo sac 3. Double fertilization: the sperm cell has two nuclei; one to produce zygote and one to produce endosperm 4. Vessel elements in xylem efficient water conducting cells Magnoliophyta - Flowering Plants Classification of Angiosperms Relationships of flowering plants are now well known based on DNA sequence evidence - APG (Angiosperm Phylogeny Group) classification system is standard. Many books (including most manuals and floras) use older classification systems - changes in families (names and genera) are not uncommon. Traditionally the flowering plants are called Magnoliophyta and were used to be divided into two classes - dicots and monocots. This is an artificial separation and no longer is used. 1 The Flower • The outstanding and most significant feature of the flowering plants is the flower • Understanding floral structure and names of the parts is important in recognizing, keying, and classifying species, genera, families. The Flower 1. Peduncle: floral stalk, the stem supporting the flower; sometimes referred to as the pedicel 2. Receptacle: modified floral stem or axis from which arise the floral appendages or modified leaves 3. Sepal: the outer most whorl of leaves, typically green and protect the inner floral parts in buds; collectively all sepals are called the calyx What is the flower? Flower: highy specialized shoot = stem + leaves. In flowers the shoot is highly modified and determinate (ceased to grow) and houses the reproductive structures. from Schleiden 1855 4. Petal: the second whorl of leaves, typically brightly colored and and assist in attracting pollinators, collectively called the corolla 5. Perianth: collective term for sepals and petals; if perianth parts cannot be differentiated into sepals and petals, that is, they look so much alike, then they are called tepals The Flower 6. Filament: slender stalk of the stamen supporting the anther; permits exsertion of pollen out of flower 7. Anther: fertile portion of stamen that dehisces to release pollen grains; composed of anther sacs 8. Stamen: the male structure of flower comprising filament and anther; collectively, all the stamens are referred to as the androecium (= ‘house of males’) The Flower 6. Filament: slender stalk of the stamen supporting the anther; permits exsertion of pollen out of flower 7. Anther: fertile portion of stamen that dehisces to release pollen grains; composed of anther sacs 8. Stamen: the male structure of flower comprising filament and anther; collectively, all the stamens are referred to as the androecium (= ‘house of males’) Nectaries often near base of stamens; produce nectar reward for visitors who will move pollen (‘pollinators’) 2 The Flower 9. Ovary: basal portion of pistil that contains ovules; at maturity becomes fruit with seeds 10. Ovules: fertile portions of pistil that contain female gametophyte (embryo sac); develop into seeds after fertilization 11. Style: slender stalk of pistil above ovary that the pollen tubes must pass through to reach eggs in ovules 12. Stigma: receptive portion at top of style that receives and recognizes pollen 13. Pistil: flask-shaped, female structure comprising three main parts; often referred to as carpel(s); all pistils (1 or more) are referred to as the gynoecium (= ‘house of females’). The Flower 9. Ovary: basal portion of pistil that contains ovules; at maturity becomes fruit with seeds 10. Ovules: fertile portions of pistil that contain female gametophyte (embryo sac); develop into seeds after fertilization 11. Style: slender stalk of pistil above ovary that the pollen tubes must pass through to reach eggs in ovules 12. Stigma: receptive portion at top of style that receives and recognizes pollen 13. Pistil: flask-shaped, female structure comprising three main parts; often referred to as carpel(s); all pistils (1 or more) are referred to as the gynoecium (= ‘house of females’). What is the difference between pistil and carpel? The Flower • If 2 ‘leaves’ in one flower each separately form carpels, • then the flower has 2 carpels and 2 pistils, • gynoecium is apocarpic (separate carpels) The Flower 1 floral ‘leaf’ in gynoecium Folded ‘leaf’ 1 carpel = 1 pistil This gynoecium is monocarpic (one carpel) Caltha palustris - Marsh marigold 9 fruits (pistils) from 1 flower Gynoecium is apocarpic with 9 carpels or 9 pistils 3 The Flower The Flower Placentation types- arrangement of ovules Marginal - found in all monocarpic or apocarpic pistils 3 floral ‘leaves’ in gynoecium fuse 3 carpels = 1 pistil 3 styles This gynoecium is syncarpic 3 carpels = 1 pistil 1 style This gynoecium is syncarpic Axile - found in some syncarpic pistils The Flower Placentation types- arrangement of ovules The Flower numerical plan Parietal - found in many syncarpic pistils Free-central - found in a few syncarpic pistils perianth spiralled perianth 5-merous Basal - found in some monocarpic, apocarpic, or syncarpic pistils perianth 4-merous perianth 3-merous 4 The Flower symmetry The Flower fusion of floral parts Connation: fusion of floral parts from the same whorl Flowers radially symmetrical Flowers actinomorphic Fusion of carpels Syncarpic pistil Flowers bilaterally symmetrical Flowers zygomorphic Fusion of stamens Staminal tube Fusion of petals Corolla tube The Flower fusion of floral parts Adnation: fusion of floral parts from different whorls The Flower floral formulas - short hand notation 4 sepals (CAlyx) 4 petals (COrolla) 8 stamens (Androecium) 4 carpels (Gynoecium) Oenothera biennis Evening primrose Onagraceae 5 The Flower floral formulas - short hand notation The Flower floral formulas - short hand notation 4 sepals (CAlyx) 4 petals (COrolla) 8 stamens (Androecium) 4 carpels (Gynoecium) Carpels fused = 1 pistil 4 sepals (calyx) 4 petals (corolla) 8 stamens (androecium) 4 carpels (gynoecium) Carpels fused = 1 pistil Ovary inferior Oenothera biennis Evening primrose Onagraceae Oenothera biennis Evening primrose Onagraceae The Flower floral formulas - short hand notation Inflorescences - Floral Displays The vast majority of flowering plants possess flowers in clusters called an inflorescence. These clusters facilitate pollination via a prominent visual display and and more efficient pollen uptake and deposition than with single flowers widely spaced. 4 sepals (calyx) 4 petals (corolla) 8 stamens (androecium) 4 carpels (gynoecium) Carpels fused = 1 pistil Ovary inferior Hypanthium (+ hypanthium tube) Oenothera biennis Evening primrose Onagraceae 6 One modification of the basic raceme is to make it compound The shift from widely spaced single flowers to an inflorescence required condensation of shoots and the loss of the intervening leaves. The simplest inflorescence type would thus be indeterminate with the oldest flowers at the base and the younger flowers progressively closer to the apical meristem of the shoot. Raceme (Prunus or cherry) compound = a raceme Raceme Panicle A second modification of the basic raceme is to lose its pedicels The panicle is essentially a series of attached racemes with the oldest racemes at the base and the youngest at the apex of the inflorescence. Pedicel loss Panicle (Zigadenus or white camass) Raceme Spike 7 The spike is usually associated with congested reduced flowers and often, but not always, with wind pollination. wind pollinated insect pollinated A third modification of the basic raceme is to lose its internodes Internode loss Umbel Spike (Plantago or plantain) (Verbena or vervain) Raceme A fourth modification of the basic raceme is for the stem axis to form a head The umbel characterizes specific families (carrot and ginseng families for example). These families typically show a compound umbel smaller umbellets on a larger umbel. Stem head Umbel Head or capitulum (Cicuta or water hemlock) (Zizia or golden alexander) Raceme 8 The head or capitulum characterizes specific families - most notably the Compositae or Asteraceae. Not surprisingly, this family is closely related to families possessing umbels. Besides these indeterminate inflorescences based on the raceme, there is a series of inflorescence types based on determinate shoots (shoot can not grow up indefinitely). The simplest is the dichasium. Head or capitulum (Helianthus or sunflower) Raceme Dichasium One modification of the basic dichasium is to make it compound The dichasium inflorescence is terminated (i.e., determinate) by the oldest flower and flanked by two lateral younger flowers. compound Dichasium Dichasium (Clematis or virgin’s-bower) Cyme 9 The cyme characterizes specific families - most notably the Caryophyllaceae - the pink or carnation family . . . or the Gentianaceae - the gentian family. Cyme Cyme (Silene or campion) (Lisianthius) A second modification of the basic dichasium is to reduce it The monochasium is most often seen in compound form as a scirpoid inflorescence. The Boraginaceae (Virginia bluebell family) is characterized by this distinctive inflorescence. reduction Dichasium Scirpoid Monochasium (Mertensia or bluebell) 10 Another specialized inflorescence is the catkin or ament A final specialized inflorescence is the spadix • unisexual cluster of small flowers • apetalous (without petals) • hard bracts around the flowers • wind pollinated • falls as a unit • thickened, fleshy spike • associated with spathe bract • frequently flowers unisexual • best developed in the aroid family (Araceae) spathe spadix [male catkin] [female catkin] (Populus or cottonwood) [male catkin] (Quercus or white oak) (Symplocarpus or skunk cabbage) (Arisaema or Jack-in-the-pulpit) 11