Plant Description
The following sequence is commonly employed during plant description.
HABITAT:
- It implies whether cultivated as an ornamental plant, a food crop or occurring in a wild state.
HABIT:
- It deals with classification of plant:
-
According to the length of life:
- Annual: [Latin annus year] Plants which grow for one season
- Biennial: Plants which grow for two growing seasons.
- Perennial: Plants which live for many years and produce seed annually.
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According to growth, size, soft and woody nature of stem:
- Herbs: Soft-stem, small in size
- Shrubs: Woody larger than herbs, bushy in nature, stem branched near the ground.
- Trees: A Perennial plant with a woody self-supporting main stem or trunk and usu unbranched for some distance above the ground Tall woody having the main stem from which branches arise.
- Climber: Plants with weak stem, climbs over support by different means.
- Runner: Plant having a weak stem, retained on the ground.
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ROOT:
- Root may be defined as, “Cylindrical plant organ which is devoid of chlorophyll, bearing no buds or leaves, and tending to grow downloads away from light.” It develops from radical part of the embryo.
- Roots are Positively Geotropic and Negatively Phototropic ie they grow downward into the soil and away from light.
Young Plant Shoots Bending Toward Light (Phototropism)
Since green plants are autotrophic, or able to manufacture their own food from water, carbon dioxide, sunlight, and inorganic molecules, they must grow in areas with available sunlight. In response to this need, green plants are phototropic, or able to grow towards a source of light.
- Roots are Positively Thermotropic and exhibit Positive Hydrotropism ie they bend in the direction of temperature and have a tendency to grow in the direction of moisture.
- When a seed germinates, radical gradually elongates and form primary roots. The primary root may give off branches, the secondary roots which in turn branch off to produce tertiary and quaternary roots.
- In dicotyledonous plants, the primary root becomes the main root and is termed as a taproot. Monocotyledonous plants, generally, lack taproot. In turn, these produce roots from the base of the stem which is strong and vigorous. These roots are known as adventitious roots.
Functions of Root:
- Anchorage
- Absorption of food from the soil
- Store food
- Absorb moisture
- Provide shelter to Nitrogen Fixing bacteria.
- Provide extra support to plant
Modifications of Root:
Fibrous:
A root system in some plants such as grasses that consists of numerous very fine branches of approximately the same length as in grasses like Cynodon dactylon: See fig
Fibrous Root
The main root of many plants divides as it grows downward. The branches, called lateral roots, further divide to form a network that anchors the plant in the ground. New growth takes place at the ends of the smallest roots. Tiny root hairs absorb water and nutrients from the soil, channeling them up to the stem and leaves of the plant through the xylem tissue at the center of the root.
Prop/Pillar and Aerial Roots:
A root that grows from the stem of a plant above the ground and helps to support it.
Roots arising from the stem are known as adventitious roots. Such roots may be seen near the base of a corn stem. Adventitious roots formed high up on a stem are termed aerial roots _see fig, or prop roots. Such roots aid in supporting the stem, as in the banyan, the mangrove, and certain orchids.
Epiphyte
Although similar in structure and function to the roots of plants living in soil, the roots of epiphytes, or air plants, are adapted for growth above the soil surface. Usually growing on the branches or trunks of trees and shrubs, where there is increased access to light, the plants develop aerial roots.
Climbing Roots:
Some plants have roots which twine around the support like tendrils eg in some spp of Ficus and Hedera helix.
Tuberous:
Thick swollen roots.
Parasitic roots:
Absorbing by penetration to host.
Conical:
Root is broad at the base and gradually taper as in Carrot, Reddish, etc
Napiform:
Very much swollen above abruptly taper lower end as in Turnip.
Nodulated:
Root with small globular swellings belonging to Leguminosae eg Pea, Gram, etc.
Stilt root:
Root arising from the lower portion of the stem and run obliquely towards the soil as in Maize, Sugarcane to fix plant into the soil.
STEM:
- A stem is the main stalk of a plant that bears buds and shoots
- A stem can be:
Erect or weak:
If weak, prostate or climbing
Special modification:
Rhizome:
Thick, fleshy, elongated, underground stem.
Corm:
Thick, fleshy, rounded, underground stem.
Bulb:
It is specialized underground shoot ie onion.
Phylloclade:
Leaf-like stem
Texture:
Herbaceous or woody
Duration:
Annual, biennial or perennial
Surface:
Smooth, waxy, spiny, prickly, glacious, or glabrous (without any projection)
Colour:
Green or dirty green.
Stems
The stem of a plant provides pathways for the distribution of water and nutrients between the roots, leaves, and other parts of the plant. The herbaceous stem of the dandelion (top, center) lacks lignin, the stiffening material in rigid, supportive woody stems. For this reason, herbaceous plants are generally limited in their physical size. Spurges and cacti (bottom, left), their leaves reduced to needles to prevent evaporation in a dry climate, consist entirely of stem material. Tubers, such as potatoes (top, right), are swollen, food-storing, underground stems that nourish growing buds. The stems of some plants are adapted for protection, as in the hawthorn (bottom, right). Others actively compete for sunlight, using touch-sensitive, curling tendrils (top, left) or other structures to climb upwards.
LEAF:
A leaf is a flat green part that grows in various shapes from the stems or branches of a plant or tree and whose main function is photosynthesis.
Simple Leaf
A simple leaf, such as this example from a maple tree, has a single leaf blade. The netlike pattern of veins visible here is characteristic of dicotyledonous plants.
Insertion:
Attachment of leaves.
Radical:
Leaves on the lower part of the stem
Cauline:
Leaves on the upper part of the stem
Ramal:
Leaves on stem
Phyllotaxis:
An arrangement of leaves on branches.
Alternate:
Leaves single at node
Opposite or whorled:
Two leaves at one node
Superposed:
If opposite with two formed
Decussate:
If opposite with four row of leaves on vertical view.
Stalked: (Petiolated)
Petiolate:
It petiole is present
Sessile:
If petiole is absent
Sub-sessile:
If short petiole is present
Stipulate:
Stipule is the leaf-like outgrowth at the base of the leaf.
Stipulate:
If stipule is present
Exstipulate:
If stipule is not present
Leaf Base:
Sheathing:
If broad
Connate:
Covering branch
Lingulate:
Tongue-shaped
Kind:
Simple:
If lamina is in one piece
Acicular:
Needle-like as in pines
Subulate:
Long, narrow stiff gradually taper as in Juniper
Linear:
Flat, long narrow as in grasses
Lanceolate:
Lance-shaped
Oval:
Lanceolate but shorter and broader
Ovate:
Egg-shaped as in Banyan
Cordate:
Heart shaped notched base
Obcordate:
Heart shaped narrow at the base.
Hastate:
Base bilobed, lobes directed outward
Sagittate:
Like arrowhead, base bilobed directed downward
Compound:
If lamina is divided into no of leaflets.
Compound Leaf
Compound leaves, although they appear to be a collection of many leaves, arise from a single bud. The leaflets fall as a group in the autumn. The leaf pictured here is from a Hercules’ club. It is pinnately compound (with paired, equally sized leaflets arising from a central blade), and doubly so, with leaflets attached to matching side stalks. The leaflets of palmately compound leaves, such as those of the horse chestnut family, radiate from a single point.
Palmate:
When leaflets come of at tip of petiole
Pinnate:
When leaflets arise from the side of rachis
Paripinnate:
Leaflets number even
Imparipinnate:
When leaflets are odd
Venation:
The arrangement of veins and veinlets
Unicostate:
If single midrib in the lamina
Multicostate:
If more than one midribs are present
Reticulate:
If veins form a network
Parallel:
If veins run parallel
Monocot Leaf
Leaves of monocotyledonous plants, such as the palm pictured here, usually have parallel leaf veins. Dicots show netlike venation. Palm leaves, native to windy environments with little rainfall, have tough leaves that resist drying out.
The margin of Lamina:
Entire:
Perfectly even
Dentate:
Margin with sharp teeth
Serrate:
Margin with small sharp teeth
Crenate:
Margin with round teeth
Bidentate:
Margin with teeth which are further divided into dentate, crenate, or serrate manner.
Spiny:
Margin with spines
Hairy:
Margin with hair
Incised:
With more or less deep incision.
Apex:
Tip of leaf
Accuminate:
Tip suddenly narrow eg Peepal
Acute:
Tapering to form an acute angle
Obtuse:
Tip round
Cuspidate:
Prolonged into sharp, stiff spine like eg Yucca
Truncate:
Flat apex
Mucronate:
Tip abruptly ends in a small pointed projection eg Cassia fistula
Emarginate:
Deep notched at the tip of midrib
Retuse:
Slightly notched at tip
Pine Needles
The blue pine has needles that grow in bundles of five. Pine needles are actually highly modified leaves that are not shed each year and can remain on the tree for long periods. Each needle has a tough outer layer called the cuticle, which in turn has a waxy coating that helps prevent water loss.
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