EVOLUTION AND DIVERSITY IN PLANTS

 EVOLUTION AND DIVERSITY IN PLANTS

Requirements for Successful Life on Land

Sturdy tissues to hold plants upright

Structures to absorb water, minerals, oxygen and carbon dioxide  

Tissues to transport water and food to cells that cannot make their own

Coating to conserve water and prevent plants and gametes from drying out

Structures to better protect gametes

New methods to improve chances of fertilization

Structures to protect developing plant

Characteristics Plants Share with their Protist Relatives, Algae

 Multicellular, eukaryotic, photosynthetic autotrophs  Contain chlorophyll a, b, and carotenoid pigments.  Cell walls contain cellulose, Store starch in specialized vacuoles

 Characteristics;bryophytes

they may grow as epiphytes (plants that grow on other plants). Many are pioneer plants, growing on bare rock. Many mosses are quite resistant to desiccation. They can lose water in the dry season, remain alive and then imbibe water when it rains. Similarly, many temperate mosses can survive freezing and thawing without damage. 

A. Sporophyte has no direct connection with the ground, but is "parasitic" on the gametophyte. 

B. Gametophytes are always small - rarely over a few inches, and are photosynthetic. 

C. Although bryophytes are land plants, they are still dependent upon water for fertilization, as the sperm swim in a water film. 

D. Because of their small size, they do not need, or have specialized conduction systems. 

E. The diploid sporophyte usually consists of a basal foot, an elevating seta and a terminal sporangium - the capsule. Spores are produced as a direct result of meiosis. 

F. True roots, stems and leaves lacking. Consists rather of rhizoids, caulalia, & phyllidia. 

G. Gametophytes homothallic or heterothallic.

. General life history Archegonia flask-shaped with venter, neck, ventral canal cell, neck canal cells and cover cells. Egg in venter.At maturity, the last 3 structures disintegrate, opening the neck for the entrance of the sperm. Antheridia consist of rounded structure consisting of a single layered jacket surrounding a central mass of cells - androcytes.Each changes into slender biflagellated sperm. The sperm are released when the antheridium ruptures, thus allowing them to swim freely in a water film. After fertilization, many divisions form a multicellular embryo which is nourished by the gametophyte.The embryo grows & forms a mature sporophyte, within which sporogenous tissue will form spore tetrads, which in turn are released as the spores, forming either the gametophyte, or the protonema, which in turn forms the typical gametophyte.

Bryophytes all require moist conditions for at least part of their life cycle. If really wet, Being prostrate, bryophytes have much of their surface in contact with the substratum and readily absorb moisture this way. Water often is drawn along the surface of these plants by capillary action and this external water movement is important. In certain mosses, specialised transport cells, hydroids and leptoids, analogous to the xylem and phloem of vascular plants, are found at the centre of the stemGases simply diffuse across the plant surface but liverworts also have special pores which are permanently open for gas exchange. Hornworts and certain mosses also have stomata on their capsules (sporophytes)

Plants’ Unique Derived Traits

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Support	Lignin - a strong polymer in cell walls- helps plants to grow tall and transport materials
Structures to absorb  CO2, and O2	Stomata - pores to exchange CO2, O2, and  H2O
Structures to absorb minerals, H2O	True roots
Transportation for nutrients and water	Vascular tubes - phloem (glucose) and xylem (water and minerals)
Dehydration protection for plant	Cuticle - waxy waterproof coating to prevent dessication and protect from microbes…and stomata
Dehydration protection for gamete	Sporopollenin - a protective waxy polymer coating spores
Improved gamete protection	Seed casings from gametangia to cones to seeds
Improved embryo protection	Zygotes develop into embryos  inside archegonia absorbing nutrients from mother plant Embryos packaged inside seeds – an embryo + food pantry within a resistant coat
Improved fertilization	From flagellated swimming sperm to structures for wind and animal dispersal
Internal growth areas for specialized tissues	Apical Meristems - growth plates at the tips of shoots and roots

In 1682, John Ray published his Methodus Plantarum Nova, in which Dicotyledones and Monocotyledones were first given formal taxonomic standing. This system was popularized by the French botanist Antoine Laurent de Jussieu in his Genera Plantarum of 1789, a work which improved upon, and gradually replaced, the system of plant classification devised by linnaeus.

Monocots	Dicots (aka Eudicots)
A. one cotyledon (seed leaf for food storage) B.  Parallel veins in leaves C.  Petals arranged in groups of threes D. Vascular bundles scattered E.  Fibrous branching roots F.  Examples - grasses, lilies, orchids, corn,      wheat, rice	A. two cotyledons, more numerous B.  Branched veins C.  Petals arranged in groups of 4 or 5 D.  Vascular bundles form a ring E. Main taproot F. Examples - beans, pears, potatoes, roses, cacti,      oaks

  Number of cotyledons -- The number of cotyledons found in the embryo is the actual basis for distinguishing the two classes of angiosperms, and is the source of the names Monocotyledonae ("one  cotyledon") and Dicotyledonae ("two cotyledons"). The cotyledons are the "seed leaves" produced by the embryo. They serve to absorb nutrients packaged in the seed, until the seedling is able to produce its first true leaves and begin photosynthesis.  Pollen structure -- The first angiosperms had pollen with a single furrow or pore through the outer layer (monosulcate). This feature is retained in the monocots, but most dicots are descended from a plant which developed three furrows or pores in its pollen (triporate). Number of flower parts -- If you count the number of petals, stamens, or other floral parts, you will find that monocot flowers tend to have a number of parts that is divisible by three, usually three or six. Dicot flowers on the other hand, tend to have parts in multiples of four or five (four, five, ten, etc.). This character is not always reliable, however, and is not easy to use in some flowers with reduced or numerous parts.  Leaf veins -- In monocots, there are usually a number of major leaf veins which run parallel the length of the leaf; in dicots, there are usually numerous auxillary veins which reticulate between the major ones. As with the number of floral parts, this character is not always reliable, as there are many monocots with reticulate venation, notably the aroids and Dioscoreales.  Stem vascular arrangement -- Vascular tissue occurs in long strands called vascular bundles. These bundles are arranged within the stem of dicots to form a cylinder, appearing as a ring of spots when you cut across the stem. In monocots, these bundles appear scattered through the stem, with more of the bundles located toward the stem periphery than in the center. This arrangement is unique to monocots and some of their closest relatives among the dicots  Root development -- In most dicots (and in most seed plants) the root develops from the lower end of the embryo, from a region known as the radicle. The radicle gives rise to an apical meristem which continues to produce root tissue for much of the plant's life. By contrast, the radicle aborts in monocots, and new roots arise adventitiously from nodes in the stem. These roots may be called prop roots when they are clustered near the bottom of the stem.  Secondary growth -- Most seed plants increase their diameter through secondary growth, producing wood and bark. Monocots (and some dicots) have lost this ability, and so do not produce wood. Some monocots can produce a substitute however, as in the palms and agaves.

lSpecial Adaptations of Angiosperms

lFlowering plants are the most numerous of the modern plants. Many of their flowers, designed to attract pollinators, are the product of coevolution with insects (and other animals) resulting in an efficient means of uniting sperm and egg. Their fruits are often designed to aid in the dispersal of their seeds.

lPollinationlPollen grains may be transferred from anther to stigma without the help of moisture.

lwind and millions of tiny, buoyant pollen grains lcoevolution between flowers and pollinators such as bees Double FertilizationlA tube emerges from the coat of the pollen grain (male gametophyte) and digests its way through the style.lGenerative and tube nuclei become sperm.

lThe sperm enter egg sac via pollination tube through micropyle lone sperm unites with egg forming the zygotelthe other sperm nucleus unites with a polar cell containing two nuclei- endosperm is formed (triploid tissue). Floral parts - Flower = a determinate shoot of the sporophyte of a higher plant that is modified for reproduction and consists of a shortened axis bearing modified leaves. Even the ancient Greeks recognized that floral parts were modified leaves

References

• Bakker,Robert.(1978).dinosaur feeding behaviour and orgin of flowering plant.Macimillan london
• Stevens.P.F.(2011).Angiosperm phylogeny Website (at missouri botanical Garden)
• Dutta, A.C. 1999. Botany for Degree Students. Oxford     University Press, Calcuta.
• Pandey, SN; Trivedi, PS and Misra, SP. 1996. A text book of botany. Vol I. Vikas Publishing House PVT ltd.
• Pandey, SN; Trivedi, PS and Misra, SP. 1998. A text book of botany. 11th revised Edition Vol II. Vikas Publishing House PVT ltd.
• Jensen, WA & Salisbury, FB. Botany: An ecological Approach. Wadsworth Publishing Company inc., California.
• Gorge B. Johnson 2000. The living world. Second edition
• Murray W. Nabors 2004. Introduction to Botany. Pearson Benjamin Cummings. University of Mississippi
• Berg, LR. 1997. Introductory Botany: Plants, People and the Environment. St Pettersburg Junior college.