Presentation on theme: "Flowers in Review. Basic Flower A flower described: A characteristic feature of the angiosperms is the grouping of sexually reproductive structures."— Presentation transcript:
A flower described: A characteristic feature of the angiosperms is the grouping of sexually reproductive structures with sterile auxiliary ones into a single unit known as the flower. Most consider the flower to represent a shortened branch bearing several kinds of modified leaves.
A flower described: Part II The sepals and petals (calyx and corolla) are sterile (non-reproductive). The inner two whorls of a flower, stamens (microsporophylls) and carpels (megasporophylls) are reproductive. Stamens and carpels produce spores for sexual reproduction through the process of meiosis.
Perianth (the calyx and corolla collectively) The perianth is the set of sterile flower parts that surround the stamens and carpels. The perianth is biseriate if it consists of an outer ring of sepals and an inner ring of petals. The perianth is uniseriate is only one ring of perianth parts is present. If only one ring of perianth parts is present, the present parts are considered sepals, and the missing parts are considered petals.
Calyx Facts I Sepals are most commonly green and leaf-like (sepaloid), but it is not uncommon for them to have the color and texture of petals (petaloid). Sepals may be distinct or variously connate. A calyx of connate sepals is synsepalous.
Calyx Facts II The fused portion of a synsepalous calyx is a calyx tube. The separate tips of a calyx are called calyx lobes. Sepals may be entirely missing in some cases. Sepals may fall off as the flower opens (caducous sepals). Sepals may persist through various lengths of time in flowering and fruiting.
Corolla Facts The corolla is the inner of the two sterile whorls when both whorls are present. Petals are often brightly colored, but they are sepaloid (green and leaf-like) in some flowers. Generally, if the number of sepals and petals is the same, the petals alternate with the sepals.
Corolla Facts A flower that lacks petals is apetalous.
Corolla Facts A flower that has distinct (separate) petals is apopetalous.
Corolla Facts An individual petal sometimes has a thin, stalk-like basal portion called a claw and an expanded upper portion called a blade.
Corolla Facts III A flower that has connate petals into a ring or a tube may be described as sympetalous. Sympetalous corollas often have a cylindrical basal tube, a gradually expanding throat, and a flaring limb. This limb is usually lobed.
Corolla Facts IV A sympetalous corolla with bilateral symmetry is often bilabiate (two-lipped). From the side it looks like an open mouth with an upper lip (usually 2 lobes) and a lower lip (usually 3 lobes).
Androecium Facts The androecium consists of the stamens of the flower, usually arranged in a spiraled or whorled pattern. Stamens are located around the gynoecium if carpels are present (bisexual flower or perfect flower). Stamens are located in the center of the flower if the gynoecium is absent (unisexual flower or imperfect flower).
Androecium Facts Most stamens consist of a narrow thread- like filament (stalk) bearing a terminal, 2- 4 lobed sac-like anther filled with pollen. Occasionally, the filaments are absent or nearly so, and the anthers are attached directly to the receptacle (the portion of the pedicel upon which the flower parts are borne).
Androecium Facts Rarely, stamens are broad and leaf like. In most plants, an anther is composed of 2-4 pollen sacs joined by a sterile region called the connective. Stamens may be fertile or sterile. Fertile stamens produce pollen. Staminodes (sterile stamens) have lost the ability to make pollen and are extremely variable in form and size. Staminodes may secrete nectar.
Androecium Facts Stamens may be distinct and free or variously fused to each other (connate) or to other parts of the flower (adnate).
Androecium Facts If the filaments of all the stamens are connate into a ring, the stamens are monadelphous (united in one group).
Androecium Facts In many members of the Fabaceae family, the stamens are diadelphous (in two groups). In such plants, there are ten stamens, nine of which are connate by their filaments into a U-shaped tube and one which is distinct. In several other families, stamens are connate in bunches, often with several to many stamens each.
Androecium Facts In the very large sunflower (Asteraceae) family and a few other families, the filaments are distinct, but the anthers are connate, forming a tube that surrounds the style.
Androecium Facts Stamens may be adnate to other parts of the flower. In this illustration, the stamens are adnate to the corolla (petals). These are considered epipetalous stamens.
Androecium Facts The number of stamens in a flower is extremely variable. Stamens may be fewer than, equal to, twice as many, or more than twice as many as the petals.
Androecium Facts When the stamens are as many as or fewer than the petals, they are alternate with the petals if they attach between the petals.
Androecium Facts When the stamens are as many as or fewer than the petals and if they attach directly in front of the petals they are considered opposite.
Gynoecium Facts The carpels form the terminal or centermost whorl of parts on the flower. The carpels are the basic units of the gynoecium. Another term used often to describe the gynoecium is pistil.
Gynoecium Facts The gynoecium consists of the ovary, one or more stigmas (pollen receptive surfaces), and usually one or more styles (slender connections between stigma and ovary).
Gynoecium Facts Some angiosperms have only a single carpel per flower. These have a monocarpous gynoecium. Some flowers have two or more carpels. If the carpels are distinct from each other, the gynoecium is apocarpous. If the carpels are fused (connate), the gynoecium is syncarpous.
Gynoecium Facts A one-carpellate pistil is a simple pistil. Simple pistils are evident in monocarpous and apocarpous gynoeciums. When two or more carpels are connate, a syncarpous gynoecium is formed. The resulting stucture is called a compound pistil.
Placentation Placentation is the attachment of ovules (immature seeds) within the interior of an ovary. The placement of the ovules in quite variable and is dependent on the number of carpels, their degree of fusion, and evolutionary modifications of the interior of the ovary and its contents.
Ovary Position and Insertion Points The ovary is generally directly attached directly to the receptacle. The other flower whorls are also attached to the receptacle, but their apparent place of attachment may be to the rim of a hypanthium or to the sides or top of the ovary. The apparent point of attachment of the outer floral parts relative to the ovary is their place of insertion.
Ovary Position and Insertion Points If the bases of the perianth parts are attached directly to the receptacle, the insertion is hypogynous. The ovary of such a flower is superior (free from the bases of the outer parts of the flower).
Ovary Position and Insertion Point If the flower has a hypanthium, the apparent point of attachment of the outer flower parts is the rim of the hypantium rather than the receptacle. The ovary is superior.
Ovary Position and Insertion Point If the bases of the perianth parts and stamens are directly adnate to the ovary wall the insertion is epigynous (the top of the ovary). The ovary is inferior.
Ovary Position and Insertion Point If the bases of the perianth parts and stamens are adnate to the ovary wall as a hypanthium, the insertion is epigynous The ovary is inferior. A flower with an inferior ovary always has a epigynous insertion.
Nectaries Flowers that are animal/insect-pollinated often bear nectaries. These are secretory glands that exude a solution of sugars or other substances that are gathered by animals for food. Some flowers have a nectary disc that sits below or surrounds the base of the ovary. Some flowers produce nectar inside spurs that jut from the surface of the perianth part.