Abdulaziz Altaweel

Angiosperms

Division/Phylum Angiospermae is sometimes called Division Anthophyta (anthe = flower; phyto = plant) because the common name for this group is the “flowering plants.” Angiosperms are so named because the seeds are enclosed within a fruit of some sort.

Division Angiospermae contains two main classes: Class Monocotyledones (the “monocots”) and Class Dicotyledones (the “dicots”). These two classes can be distinguished in a number of ways, including:

The parts of an Angiosperm include:

1. Roots, which are generally underground and serve to absorb water and nutrients

2. Stems, which come in various types such as:

   • stolon, an above-ground “runner”

   • rhizome, an underground “runner”

   • bulb, a fleshy stem modified for nutrient storage

3. Leaves, which can be either simple or compound in form and which alternate with each other going up the stem or can be arranged opposite each other on the stem or as whorled leaves where more than two originate from the same place on the stem
   
   Leaves can be many shapes from round to heart-shaped to oblong. Leaves which are entire, all in one piece, are called simple leaves, while those divided into multiple leaflets are called compound leaves. Compound leaves with their leaflets arranged like a feather are said to be pinnately compound (pinna = wing, feather) while leaves with their leaflets arranged like a person’s fingers are said to be palmately compound. Leaves that arise from the branch/stem in pairs are referred to as opposite leaves, while those which alternate sides up the stem are referred to as alternate leaves, and if more than two leaves arise from the same spot, those leaves are said to be whorled.

4. Flowers, which are the reproductive structures of an angiosperm and consist of four whorls of modified leaves (from outside in):

   • Sepals (sepi = fence in) (which collectively are called the calyx), which are often small and green but are colored like the petals in tulips and lilies, and which generally enclose the flower before it opens

   • Petals (petal = a leaf, spread out, flat) (which collectively are called the corolla) which are often brightly colored to attract pollinators (insects, birds, etc.) and may be very simple to highly modified

   • Stamens (stam(en) = anything standing upright, a thread), the “male” reproductive organs (they make microspores which turn into male gametophytes), which consist of a stalk (the filament) and a tip (the anther) where the microspores are produced and turn into pollen (anthe = flower)

   • Pistil (note spelling) or carpel (carpo = a fruit), which consists of:

     Ovary (ova, ovi = egg)

     the bottom end where seeds are produced

     Style (styl, stylo = a pillar, stake, column)

     the “stalk” portion

     Stigma (stigma = spot)

     the outer, sticky tip where pollen sticks when it lands or is placed there

   

   Botanists group species of plants (or, from the other direction, the monocots and dicots can be subdivided) based on a number of characteristics. Botanists pay particular attention to how the flowers are put together:

   A complete flower has all four layers of parts.
   An incomplete flower lacks one or more layers. These knotweed flowers lack petals (corolla).
   A perfect flower had both “sexes” — both stamens and pistil(s). A monoecious plant has perfect flowers or has both male and female flowers on the same plant (for example, Easter lily, pea, dandelion, and rose).
   An imperfect flower is lacking either the pistil or stamens. A dioecious plant has imperfect flowers on separate male and female plants (for example, marijuana, hops, persimmon, and boxelder). Note that plants such as ginkgo, a gymnosperm which doesn’t produce flowers but which has separate male and female reproductive structures on separate male and female plants, are also referred to as being dioecious.
   A regular flower is radially symmetrical.
   An irregular flower has bilateral symmetry, and is also known as a zygomorphic flower.

   Multiple flowers can be arranged or clustered in various ways, including:

5. Fruit, which is a ripened (mature) ovary (in which seeds develop/are found) and which serves as protection and means of dispersal for the seeds
   various types of fruits include:

   • Simple fruits arise from one ovary in one flower. Examples include cucumber, peapod, walnut, tomato, orange, cherry, apple, dandelion, and maple “helicopter.” There are a number of types of simple fruit, each with its own official name.

   • Aggregate fruits arise from several ovaries in one flower. Examples include raspberry and strawberry.

   • Multiple fruits arise from ovaries in several, tightly-clustered flowers which grow together into one “fruit.” Examples include pineapple, mulberry, and breadfruit.

   

Angiosperm Life Cycle

Angiosperms have alternation of generations with the 2n sporophyte being the dominant generation. The anthers, which are the equivalent of microsporangia, produce microspores by meiosis, and the microspores develop into male gametophytes (= pollen).

The ovaries, which are the equivalent of megasporangia, produce megaspores which grow into female gametophytes, each of which then produces an egg.

Note that technically the “sex organs” of a plant aren’t because they produce spores (micro- or mega-) which turn into male or female gametophytes. The gametophytes bear the true sex organs, such as they are, and are where eggs or sperm are actually produced.

By some means (wind or an animal pollinator), the pollen is transferred to the stigma of the pistil, and a pollen tube grows down into the ovary. Eventually, two sperm nuclei travel down the pollen tube. Pollination is the transfer of the male gametophyte (pollen) to the stigma of the female, while fertilization is when the sperm nucleus and egg nucleus unite

Angiosperms have an unusual thing called double fertilization. When the sperm nuclei reach the female gametophyte, one sperm nucleus and the egg cell unite to form a new 2n zygote (which grows into an embryo). The other sperm nucleus and two nuclei from the female gametophyte join to form 3n endosperm which often serves as food for the embryo.

The embryo sporophyte consists of:

1. one or two nutrient-storage areas called cotyledons which are in contact with (and absorb nutrients from) the 3n endosperm. Seeds of some species store their nutrients primarily in the endosperm, having very small cotyledon(s), while others have most of their nutrients stored in their cotyledons and the endosperm is very small.

2. the epicotyl (epi = upon, over), which is the region above the cotyledon(s), and which will become the stem and leaves,

3. the hypocotyl (hypo = under, beneath), which is the region under the cotyledon(s). The lower end of the hypocotyl, which becomes the root system, is called the radicle (radix = root) and will become the roots.

In general, monocots tend to store food in their endosperms, and nutrients are transferred to the cotyledon only as needed. In contrast, many (not all) dicots tend to store food in their cotyledons with the endosperm being reduced to a papery coating around the embryo.

 Angiosperms can be Annuals, Bienniasl and Perennials:

Annuals: An annual plant is a plant that usually germinates, flowers, and dies in one year. True annuals will only live longer than a year if they are prevented from setting seed. Some seedless plants can also be considered annuals even though they do not grow a flower. ^[1]

In gardening, annual often refers to a plant grown outdoors in the spring and summer and surviving just for one growing season. Many food plants are, or are grown as, annuals, including most domesticated grains. Some perennials and biennials are grown in gardens as annuals for convenience, particularly if they are not considered cold hardy for the local climate. Carrot, celery and parsley are true biennials that are usually grown as annual crops for their edible roots, petioles and leaves, respectively. Tomato, sweet potato and bell pepper are tender perennials usually grown as annuals.

Ornamental annualer perennials commonly grown as annuals are impatiens, wax begonia, snapdragon, Pelargonium, coleus and petunia. Some biennials that can be grown as annuals are pansy and hollyhock.

One seed-to-seed life cycle for an annual can occur in as little as a month in some species, though most last several months. Oilseed rapa can go from seed-to-seed in about five weeks under a bank of fluorescent lamps in a school classroom. Many desert annuals are termed ephemerals because their seed-to-seed life cycle is only many weeks. They spend most of the year as seeds to survive dry conditions.

Biennials: A biennial plant is a flowering plant that takes two years to complete its biological lifecycle. In the first year the plant grows leaves, stems, and roots (vegetative structures), then it enters a period of dormancy over the colder months. Usually the stem remains very short and the leaves are low to the ground, forming a rosette. Many biennials require a cold treatment, or vernalization, before they will flower. During the next spring or summer, the stem of the biennial plant elongates greatly, or “bolting bolts”. The plant then flowers, producing fruits and seeds before it finally dies. There are far fewer biennials than either perennial plants or annual plants.

Under extreme climatic conditions, a biennial plant may complete its life cycle in a very short period of time (e.g. three or four months instead of two years). This is quite common in vegetable or flower seedlings that were exposed to cold conditions, or vernalized, before they were planted in the ground. This behavior leads to many normally biennial plants being treated as annuals in some areas. Flowering can be induced in some biennials without vernalization by application of the plant hormone gibberellin, but this is rarely done commercially. 

Perennials: A perennial plant or perennial (Latin per, “through”, annus, “year”) is a plant that lives for more than two years. When used by gardeners or horticulturalists, this term applies specifically to perennial herbaceous plants. Scientifically, woody plants like shrubs and trees are also perennial in their habit.

Perennials, especially small flowering plants, grow and bloom over the spring and summer and then die back every autumn and winter, then return in the spring from their root-stock rather than seeding themselves as an annual plant does. These are known as herbaceous perennials. However, depending on the rigors of local climate, a plant that is a perennial in its native habitat, or in a milder garden, may be treated by a gardener as an annual and planted out every year, from seed, from cuttings or from divisions.

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