Morphology of Flowering Plants-I

Morphology (Morphe = form + logos = study). It deals with the study of forms and features of different plant organs like roots, stems, leaves, flowers, seeds, fruits etc.

The body of a typical angiospermic plant is differentiated into:

an underground root system
an aerial shoot system.

The shoot system consists of stem (including branches), leaves, flowers and fruits.

The roots, stems and leaves are vegetative parts, while flowers constitute the reproductive part.

CLASSIFICATION OF PLANTS

Depending upon their life span, plants are classified as –

Annuals – Complete their life cycle in one year or single growing season or few weeks to a few months. They pass the unfavorable period in the form of seeds e.g. Mustard, Pea.
Biennials – Complete their life cycle in two years-growing, vegetative and storing food in the first year, flowering and fruiting in the second year. They die off after producing flowers and fruits e.g. Radish, turnip, carrot is biennial in colder areas. They become annual in warmer places.
Perennials – Survives for several years. These plants usually bear flowers and fruits every year and do not die after producing flowers. e.g. Mango, Banana, Guava

ROOT

Radicle comes out/arise from the seed coat in the form of soft structure and move toward the soil. It develops and forms primary root.

General Characters

Roots are non-green, underground, (+) geotropic, (–) phototropic and (+) hydrotropic.
Roots do not bear buds.
Buds present for vegetative propagation in sweet potato (Ipomea) and Indian red wood (Dalbergia)
Roots do not bear nodes and internodes.
Roots have unicellular root hairs.

Types of Roots

Roots are of two types

Tap root: It develops from radicle and made up of one main branch and other sub branches. The primary roots and its branches constitute tap root system. e.g. Dicot roots.
Adventitious roots: In some plants, after sometime of the growth of tap root which arises from radicle, stops and then roots, develop from other part of plant, which are branched or unbranched, fibrous or storage, are known as adventitious roots and constitute fibrous root system. e.g. Monocot roots.

Regions of Roots

Morphologically four distinct regions are present in roots.

Root cap: It is terminal structure. It protects tender apex of root.
Meristematic zone: Cells of this regions are very small and thin walled. They divide repeatedly and increase cell number
Elongation region: The cells proximal to meristematic zone undergo rapid elongation and enlargement and are responsible for rapid growth of roots.
Maturation region: Cells proximal to region of elongation gradually differentiate and mature. Root hairs are present in maturation zone.

Modification of Roots

Modified tap root for storage:

Fusiform roots: These roots are thicker in the middle and tapered on both ends. In this type of roots both hypocotyl and root help in storage of food. e.g. Radish.
Conical roots: These roots are thicker at their upper side and tapering at basal end. e.g. Carrot.
Napiform: These roots become swollen and spherical at upper end and tapered like a thread at their lower end. e.g. Turnip (Brassica rapa), Sugarbeet
Tuberous root: Such roots do not have regular shape and get swollen & fleshy at any portion of roots. e.g. Mirabilis.
Nodulated root: Nodules are formed on branches of roots by nitrogen fixing bacteria, (Rhizobium). e.g. Plants of leguminosae family (Papilionatae) – Pea.
Respiratory roots: Halophyte or mangrove grow in oxygen deficient marshy area. Some branches of tap root in these plants grow vertically & comes out from soil. These roots are called pneumatophores through which air entered inside the plant. e.g. Rhizophora, Heritiera, Sonaratia and other mangrove plant.

Modification of adventitious roots:

Storage adventitious roots

Tuberous root: When food is stored in these roots, they become swollen and form a bunch. e.g. Sweet potato (Ipomea batata)
Fasciculated: Roots arise in bunch (cluster) from lower node of the stem and become fleshy e.g. Dahlia, Asparagus.
Nodulose: In this type, tips of roots swell up. e.g. Melilotus, Curcuma amoda.
Beaded or moniliform: When root swells up like a bead at different places after a regular interval. e.g. Vitis, Momordica (Bitter gourd), Portulaca.
Annulated: Roots having series of ring like swellings e.g. Psychrotia

Modifications for other purpose

Stilt roots or brace roots: When root arises from lower nodes and enter in soil obliquely, known as stilt roots e.g. Maize, Sugarcane, Pandanus (screwpine)
Prop root or pillar roots: when root arises from branches of plant and grows downward towards soil. It functions as supporting stem for the plant. e.g. Banyan.
Buttress root: Such roots appear from the basal part of stem and spread in different directions in the soil. e.g. Ficus, Bombax, Terminalia. It is a characteristic feature of tropical rain forest.
Climbing roots: These roots arise from nodes and helps the plant in climbing. e.g. Money plant (Pothos), Betel, Black pepper, Techoma.
Foliar roots or Epiphyllous roots: When roots arise from leaf they are called as foliar roots. e.g. Bryophyllum, Bignonia.
Sucking or haustorial roots or Parasitic roots: In parasitic plant roots enter in the stem of host plant to absorbed nutrition from host. e.g. Dendrophthoe, Cuscuta, Viscum.
Assimilatory roots: The aerial roots of Tinospora and submerged roots of Trapa (Water chestnut) become green and synthesize food. Podostemon also has green assimilatory roots.
Hygroscopic roots: These are found in epiphytes, especially in orchids and help in absorption of moisture from the atmosphere using special tissue called velamen. e.g. Orchids, Banda
Contractile roots: They shrink 60 – 70% of the original length and bring underground organ at proper depth in the soil e.g., corm of Crocus (saffron), Fresia.
Root thorns: These are hard, thick and pointed thorns e.g. Pothos armatus.
Reproductive roots: These are fleshy, adventitious roots used for vegetative reproduction e.g., sweet potato (Ipomea batata), Dahlia.
Leaf roots: In Salvinia, one leaf of each node modifies into root like structure for balancing the plant in water.

Functions of Root

Fixation (Primary function)
Absorption of water and minerals
Storage of food
Conduction of water
Photosynthesis and respiration

STEM

Stem is a part of plant which lies above from surface of soil i.e. it shows negative geotropic growth. It has nodes and internodes. Branches, leaf, flower bud and bracts are developed from nodes. Stem arises from plumule.

Forms of Stem

Caudex: It is unbranched, erect, cylindrical stout stem and marked with scars of fallen leaves. Crown of leaves are present at the top of plant. e.g.: Palm
Culm: Stem is jointed with solid nodes & hollow internodes. e.g. Bamboo (Graminae)
Excurrent: The branches arise from the main stem in acropetal succession and the tree assumes a cone like appearance e.g. Pinus, Eucalyptus, Casuarina, etc.
Decurrent (Deliquescent): The lateral branches grow more vigorously and outcompetes the main trunk, giving a dome-shaped appearance, e.g., mango (Mangifera indica), shishem (Dalbergia sissoo) and banyan (Ficus bengalensis).

Types & Modification of Stem

Aerial stems (Epiterranean stem)

It may be reduced, erect and weak.

Reduced – Stem reduced to a disc. e.g., Radish, Carrot, Turnip.
Erect stem - It is strong and upright e.g., maize, wheat, mango.
Weak stems – These are thin, soft and weak and need support. They can be upright or prostrate.
Creepers – The stem creeps on earth and the roots arise at the nodes, e.g., Grasses, Strawberry, Oxalis.
Trailers – The stem creeps on the ground, but the roots do not arise at the nodes. They may be of two types:
Prostrate or procumbent – The stem creeps on ground totally, e.g., Evolvulus, Tribulus.
Decumbent – When prostrate stem projects its tip, e.g., Portulaca, Linderbergia.
Lianas (Stem climber). Woody perennial climbers found in tropical rain forests are lianas. They twin themselves around tall trees to secure sunlight, e.g., Hiptage, Bauhinia vahlii (Phanera).
Climbers – Plants are with long weak stem and have organs of attachment to climb the object. They may be of following type.
Rootlet climbers – Roots produced at nodes help in climbing e.g., Tecoma, Pothos, Piper betal (pan).
Hook climbers – In Bougainvillea, Duranta and Carrisa, the thorn is modification of axillary vegetative bud which helps in climbing. In Bignonia, terminal leaflet is converted into hook.
Tendril climbers – Tendrils are thread like structure which help the plants in climbing. Tendrils are modifications of:
Entire leaf e.g. Lathyrus sativus.
Leaflet e.g. Pisum sativum
Petiole e.g. Clematis, Nepenthes.
Stipule e.g. Smilex.
Leaf apex e.g. Gloriosa
Inflorescence e.g. Antigonon.
Stem e.g., Vitis (grapevines), gourds, Passiflora (modified axillary bud).
Twiners – The stem body twines around the support without any special organ of attachment. e.g., Cuscuta, Dolichos

Sub-aerial modification:

Runner – When stem grows and spread on the surface of soil. Roots are developed at lower side and leaves from upper side from node e.g. Cynodon dactylon (Doob grass), Oxalis
Stolon – In it branches are small and stem condensed and grow in all direction. After sometime, of growing, their apical region comes out from the soil. e.g. Fragaria (Wild strawberry), Jasmine Peppermint.
Sucker – In it the main stem grow in the soil horizontally and branches develop obliquely from nodes above the soil, e.g. Mint, Pineapple, Chrysanthemum.
Offset – A lateral branch with short internode and each node bearing a rossette of leaves and tuft of roots at base. e.g. Pistia, Eichhornea.

These modifications are also involved in vegetative reproduction

Underground modification

This type of modification occurs generally for food storage and vegetative propagation.

Tuber – The tips of underground branches become swollen in the soil. Eyes are found on then which are axillary buds and covered with scaly leaves. e.g. Potato, Helianthus tuberosus
Rhizome – It is fleshy and horizontally stem found below in soil. Small nodes and internodes are found which are covered by scaly leaves. e.g. Ginger, Canna, Water lily, Banana.

Special stem modification:

Phylloclade – It is green photosynthetic flattened or rounded succulent stem with leaves either feebly developed or modified into spines e.g., Opuntia, Casuarina, Euphorbia, Cactus.
Thorn – It is modification of axillary bud, e.g., Bougainvillea, Duranta, Carissa. Thorns of Alhagi possess flowers, while thorns of Duranta bears leaves.
Cladode – Phylloclade usually having one or two internode long & succulent is called cladode, e.g., Asparagus, Ruscus.
Stem tendril – it is a leafless, spirally coiled structure found in climbers. It may be a modification of Axillary bud, e.g. Passiflora or terminal bud e.g., Vitis.
Bulbils – A condensed, axillary fleshy bud is called bulbils. It helps in vegetative reproduction. e.g. Dioscorea, Globba, Agave, Oxalis.

Functions of Stem

The main function of the stem is spreading out branches bearing leaves, flowers and fruits. It conducts water, minerals and photosynthates. Some stems perform the function of storage of food, support,
Protection and of vegetative propagation.
The leaf is a lateral generally flattened structure borne on the stem. The leaves develop from the nodes.
Their main function is photosynthesis and food making, axillary buds are found in its axil. All the leaves of a plant are known as phyllome. Axillary bud later develops into a branch. Leaves originated from shoot apical meristem and are arranged in acropetal order.

LEAF

Leaf is divided into 3 main parts:

Leaf Base (Hypopodium)

Leaves are attached to stem by leaf base.
In some plants, leaf base becomes swollen and is called pulvinus which is responsible for sleep movement e.g., Cassia, Mimosa, bean.
In some plants, leaf base expands into sheath (Sheathing leaf base), e.g., grasses and banana (monocots).
When the leaf base partially encloses the stem, it is called semi amplexicaul e.g., Prickly poppy, Calotropis procera (Madar).
It completely encloses the stem, it is called amplexicaul e.g., Sonchus, Polygonum.

Petiole (Mesopodium)

The part of leaf connecting the lamina with the branch of stem. Petiole help to hold the blade to light.
In Eichhornia petiole swell and in citrus it is winged.
Petiole is modified in tendrils in Nepenthes.
In Australian acacia petiole is modified in phyllode.
Long thin flexible petiole allows leaf blade to flutter in air, thereby cooling the leaf and bringing fresh air to leaf.

Lamina (Epipodium)

It is a broad and flattened part of leaf. Its main functions are photosynthesis and transpiration.

Shape of lamina are:

Acicular – Lamina is long and pointed, like a needle. e.g. Pinus
Lanceolate – In this type lamina is pointed or narrower at the ends while broader in the middle. e.g. Bamboo, Nerium
Linear – The lamina is long and narrow having parallel margins. e.g. Grass
Ovate – In this type lamina is egg-shaped having broad base with slight narrow top. e.g. Ocimum, Banyan, China rose.

Cordate – Its shape is like a heart. e.g. Betel.
Oblong – Long and broad lamina. e.g. Banana
Sagittate – The lamina is triangular. e.g. Sagittaria
Spathulate – The lamina is broad spoon shaped. e.g. Calendula

Orbicular or Rotund – In this types the lamina is spherical. e.g. Lotus.
Elliptical or Oval – In this type the middle part of lamina is broad while the ends are narrow and oval. e.g. Guava.
Oblique – In this types midrib divides, lamina into two unequal halves. e.g. Bignonia, Neem.

Stipules

Leaves of some plants have lateral appendages on either side of leaf base, known as stipules. If stipules are present in leaf it is called stipulated leaf, if it is absent then leaf is called exstipulated.

Stipules are of various types –

Free lateral – They are independently present on both sides of leaf base. e.g. Hibiscus rosasinensis (China rose)
Interpetiolar – When two leaves are meet oppositely at the node then nearest stipules of each leaf join with each other. In this way, only two stipules of two leaves are found in place of four. e.g. Ixora, Anthocephalus.
Intrapetioler – In this type both stipules of a single leaf join with each other to form a single stipule. e.g. Gardenia
Foliaceous – These types of stipules form a leaf like structure. e.g. Pea
Scaly – Stipules are dry, small and paper like. e.g. Desmodium
Spiny – Stipules modified into spine. e.g. Zizyphus (Beri), Acacia.
Ochreate – When both stipules of leaf combine and form a tube-like structure, it is called ochreate. e.g. Polygonum
Adnate – Both stipules are attached with petiole. e.g. Rose
Tendrillar – Stipules are modified into tendrils like structure. e.g. Smilax
Bud scale – Protect the young Bud. e.g. Ficus

Types of Leaves

Foliage leaf – They are usually green coloured and their main function is photosynthesis.
Cotyledonary leaf – This leaf comes out during germination and helps in nutrition until the first leaf is not formed.
Scaly leaf (Cataphylls) – Such leaves are usually dry membrane like and they cannot perform Photosynthesis
Bract (Hypsophyll) – Bract are the leaves which is present in flower axis.
Bracteole – These are leaf like structure found on pedical.
Floral leaf – Sepals, petals, stamen and carpel are found in flower which are included in this type of leaf.
Perianth – In some flowers, Calyx and Corolla are not distinct and are termed as Perianth and unit of perianth is called tepal. e.g. Lily

Duration of Leaf

Persistent / Evergreen – Leaves of such plants are found in all season and do not (fall) shed combinedly. e.g. Pinus, Saraca indica, Datepalm.
Deciduous – All leaves of such plants shed at the same time e.g. Azadirachta.
Caducous – Leaves fall soon just after appearance or after opening of bud. e.g. Rose

Leaf Insertion

Cauline leaves – When the leaves are found on node of stem, then these are called cauline leaves. e.g. Maize, Hollyhock.
Ramal leaves – When leaves are found on branches, then these are called ramal leaves. e.g. Delbergia, Zizypus.
Radical leaves – During favourable season, leaves develop from the nodes of underground stem and seem that they are developing from roots. This type of leaves is known as radical leaves. e.g. Radish, Turnip.

Venation of Lamina

The arrangement of veins and veinlets in leaves (Lamina) is known as venation. It is of 2 types

Reticulate: It is found in dicots. Exception – Calophyllum, Eryngium. It has parallel venation.
Parallel: It is found in monocots. Exception – Smilax, Dioscorea, Alocasia, Colocasia. It has reticulate venation.

Reticulate venation:

In its main vein divided into various branches (veinlets) and form a net like structure. Reticulate venation is of 2-types.

Unicostate or pinnate – In this type of venation leaf have only one principal vein or midrib that give off many lateral veins which proceed toward margin and apex of lamina of the leaf and form a network.eg. Mango, guava, Peepal,
Multicostate or palmate – In this type of venation many principal veins arising from the tip of petiole and proceed towards tip of lamina. This is again two types

Multicostate divergent – Many principal veins arising from the tip of petiole, diverge from the another toward the margin of leaf blade e.g. Cotton, Caster, Cucurbita, grape.
Multicostate convergent – Many principal veins arising from the tip of petiole. At the base of leaf, they are closely arranged but diverge from one another in middle part and converge towards the apex of leaf. e.g. Camphor, Zizyphus, Tejpat, Chinarose, plum.

Parallel venation:

In this type of venation, all veins run parallel to each other and they do not from network. They are of 2 types.

Unicostate or pinnate – This type of pattern having only one principal vein, that gives off many lateral veins, which proceed toward the margin of leaf blade in a parallel manner but they do not have veinlets. e.g. Banana, Ginger, Canna.
Multicostate or palmate – Having many principal veins arising from the tip of the petiole and proceeding upwards.
Multicostate divergent – Many principal veins arising from the tip of petiole and diverge toward the margin of leaf. They do not divide into veinlets and do not form network. e.g. Coconut, Date palm
Multicostate convergent – Many principal veins arising from the tip of petiole run in a curved manner in lamina and converge towards the apex of leaf blades. e.g. – Wheat, Sugar-cane, Bamboo.
Furcate venation – The veins branch dichotomously but the reticulum is not formed by the finer branches. e.g. Adiantum (fern).

Forms of Leaves

Simple and Compound Leaf:

Simple Leaf – A leaf which may be incised to any depth, but not down to the midrib or petiole, then this type of leaf called simple leaf. e.g. Mango, China rose, Ficus, etc.
Compound leaf – A leaf in which the leaf blade is incised up to the midrib or petiole, thus dividing it into several small parts, known as leaflets. This type of leaf is known as compound leaf.

Compound Leaf

It is of two types –

Pinnately compound leaf

In this type of leaf mid rib is known as rachis. Leaflets are arranged on both sides of rachis. e.g. Neem.

It is of following types -

Unipinnate – In this type of leaf, division occurs only once and leaflets are directly attached on both sides of rachis.
- If the number of leaflet is even, then leaf is known as paripinnate. e.g. Cassia fistula, Sesbania
- If the number of leaflet is odd, it is known as imparipinnate. e.g. Rose, Neem.
Bipinnate – A twice pinnate compound leaf e.g. Acacia, Gulmohar, Mimosa.
Tripinnate – A thrice pinnate compound leaf e.g. Moringa.
Decompound – A compound leaf, which is more than thrice pinnate. e.g. Carrot, Coriander.

Palmate compound leaf

In this type incision of leaf are directed from leaf margin to apex of petiole and all leaflets are attached on the upper end of petiole.

It is of following types -

Unifoliate – When single leaflet is found. e.g. Lemon
Bifoliate – When two leaflets are present. e.g. Bauhinia, Regnelidium, Bignonia.
Trifoliate – When three leaflets are attached. e.g. Oxalis, Aegle, Trifolium
Tetrafoliate – When four leaflets are attached to the petiole. e.g. Marsilea.
Multifoliate – when more than four leaflet are found, then leaf is called Multifoliate palmate compound leaf. e.g. Silk, cotton.

Phyllotaxy

It is of following type –

Alternate or spiral – Single leaf arising at each node. e.g. Cyprus rotandus, Chinarose, mustard & Sunflower,
Opposite – Leaves occurring in pairs at the node, they may be –
Decussate: Leaves that stands at right angle to next upper or lower pair e.g. Calotropis, Mussaenda.
Superposed: Successive pairs of leaves stand directly over a pair in the same plane e.g. Psidium (guava), Ixora.
Whorled – More than two leaves at each node e.g. Nerium, Alstonia.
Heterophylly – It is the occurrence of more than one type of leaves on the same plant. It is of three types –
- Developmental Heterophylly: Leaves of different forms and shape occur at different period or places on the same plant e.g. Mustard, Sonchus, Eucalyptus.
- Environmental Heterophylly: It is aquatic adaptation which is commonly found in rooted emergent hydrophytes. In this, submerged leaves differ from the floating and aerial leaves. e.g. Limnophila,
- Heterophylla, Ranunculus aquatiles, Sagittaria.
- Habitual Heterophylly: Due to habit, mature leaves differ in their shape and incisions e.g. Artocarpus (Jack fruit).

Modification of Leaves

Leaf tendril – In it, whole leaf is modified into thin thread like structure which is called leaf tendril e.g. Lathyrus aphaca (wild pea).
Leaflet tendril – When leaflet is modified into tendril like structure than it is called leaflet tendril. e.g. Pisum sativum (Garden pea), Lathyrus odoratus (sweet pea)
Leaf spine – Leaves or any part of leaflet are modified into pointed spine. e.g. Asparagus, Opuntia, Aloe, Argemone.
Leaf scale – In it, leaves become thin, dry and form a membrane or paper like structure and serve to protect axillary buds as in Ficus and Tamarix, Ruscus, Casurina.
Leaf pitcher – Leaves of some plants are modified to pitcher shape. e.g. Nepenthes, Dischidia.
Leaf bladder – In some plant, leaves are modified into bladder like structure e.g. Utricularia.
Leaf Hooks – In some plants terminal leaflets are modified into curved hooks for helping the plant in climbing. e.g. Argemone, Opuntia, Aloe, Cat's nail (Bignonia unguis – cati)
Phyllode – In its, petiole becomes flat structure and function as normal leaf. e.g. Australian acacia.
Flashy leaves – In onion and garlic food storing flashy leaves are present.

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