Morphology of Flowering Plants: Root, Stem and Flower
Exam notes on plant morphology: root and stem modifications, leaf venation and phyllotaxy, inflorescence, flower parts, aestivation, placentation, fruits and seeds.
By GK24 Editorial Team· Published · 5 min read
Morphology is the study of the external form of a plant and of the way each part is built and modified. For a flowering plant, an angiosperm, the whole body reduces to two systems: the root system below the ground and the shoot system above it, made of stem, leaves, flowers and fruits. Examiners like this chapter because every statement in it is a fact that can be asked as a pair: which plant has which modification, which family shows which placentation, which organ a potato or a carrot really is.
The root and its modifications
A root is non-green, bears no nodes or buds, and grows towards gravity. A taproot system, with one main root and its branches, is typical of dicotyledons such as mustard and gram. A fibrous root system, a cluster of roots of similar thickness from the base of the stem, is typical of monocotyledons such as wheat and grass. Roots that arise from any part other than the radicle are adventitious, as in grass, the banyan and the money plant. From the tip upwards a root shows the root cap, the region of meristematic activity, the region of elongation and the region of maturation, which bears the root hairs that absorb water.
| Modification | Function | Example |
|---|---|---|
| Conical taproot | Food storage | Carrot |
| Fusiform taproot | Food storage | Radish |
| Napiform taproot | Food storage | Turnip and beetroot |
| Tuberous adventitious root | Food storage | Sweet potato |
| Fasciculated roots | Food storage in a cluster | Dahlia and asparagus |
| Prop or pillar roots | Mechanical support to spreading branches | Banyan |
| Stilt roots | Support to a weak stem | Maize, sugarcane and screw pine |
| Pneumatophores | Breathing in waterlogged saline soil | Rhizophora, a mangrove |
| Climbing roots | Clinging to a support | Money plant and betel |
| Root nodules | Nitrogen fixation by Rhizobium | Pea, gram and other legumes |
The stem and its modifications
A stem bears nodes, internodes and buds, is usually green when young, and grows away from gravity. Its modifications are grouped by where they lie. Underground stems store food and survive the unfavourable season: the rhizome of ginger and turmeric, the tuber of the potato whose eyes are axillary buds, the bulb of onion and garlic, and the corm of Colocasia and Amorphophallus. Sub-aerial stems spread the plant: the runner of grass, the stolon of jasmine and mint, the offset of water hyacinth and Pistia, and the sucker of chrysanthemum and banana. Aerial stems take over other work: the stem tendril of the gourd and the grapevine, which arises from an axillary bud, the thorn of Citrus and Bougainvillea, the flattened green phylloclade of Opuntia and Euphorbia, the cylindrical cladode of Asparagus and Casuarina, and the bulbil of Dioscorea and Agave.
The leaf
A leaf is a lateral, flattened outgrowth of the stem with three parts, the leaf base, the petiole and the lamina; in legumes the leaf base swells into a pulvinus. Venation is reticulate, a network, in dicots and parallel in monocots. A leaf is simple when the lamina is entire or incised but not cut up to the midrib, and compound when it is divided into leaflets: pinnately compound in neem, palmately compound in the silk cotton tree. The arrangement of leaves on the stem, the phyllotaxy, is alternate in China rose and mustard, opposite in Calotropis and guava, and whorled in Alstonia and Nerium. Leaves too are modified: into tendrils in the pea, spines in Opuntia, a flattened green phyllode in the Australian acacia, a pitcher in Nepenthes, a bladder in Utricularia and fleshy storage scales in the onion.
Inflorescence and the flower
The arrangement of flowers on the floral axis is the inflorescence. In a racemose inflorescence the main axis keeps growing and the flowers open in acropetal succession, the oldest at the base, as in radish and mustard. In a cymose inflorescence the main axis ends in a flower and the order is basipetal, the oldest at the top, as in Solanum and jasmine. Special types include the cyathium of Euphorbia, the hypanthodium of the fig and the verticillaster of Ocimum.
A flower is a modified shoot whose four whorls sit on the thalamus: the calyx of sepals, the corolla of petals, the androecium of stamens and the gynoecium of carpels. A flower cut into two equal halves along any plane is actinomorphic, as in mustard, chilli and Datura; one that can be halved along one plane only is zygomorphic, as in the pea, Cassia and gulmohar. By the position of the ovary a flower is hypogynous with a superior ovary, as in mustard and brinjal, perigynous with a half inferior ovary, as in the plum, rose and peach, or epigynous with an inferior ovary, as in guava, cucumber and the ray florets of the sunflower. The mode of arrangement of sepals or petals, the aestivation, is valvate in Calotropis, twisted in cotton and lady's finger, imbricate in Cassia and gulmohar, and vexillary in the pea and bean. Placentation, the arrangement of ovules in the ovary, is marginal in the pea, axile in tomato and lemon, parietal in mustard, free central in Dianthus and basal in the sunflower and marigold.
Fruit and seed
A fruit develops from the ovary and has a pericarp of epicarp, mesocarp and endocarp. Mango and coconut are drupes, with a stony endocarp. A fruit that develops from the thalamus along with the ovary, as in the apple, is a false fruit, and one that forms without fertilisation, as in the banana, is parthenocarpic. A dicot seed such as gram has two cotyledons and little or no endosperm, while a monocot seed such as maize keeps a large endosperm with a scutellum, a coleoptile over the shoot and a coleorhiza over the root.
Exam Point of View
This chapter is tested as one-line pairings, so learn it as lists. The single most asked item is which organ a vegetable really is: potato a stem tuber, sweet potato a root, onion a bulb, ginger a rhizome, carrot a taproot. Next come the root types, with prop roots for banyan, stilt roots for maize and screw pine and pneumatophores for mangroves. Phylloclade against cladode against phyllode is a favourite trap, as is reticulate against parallel venation for dicots and monocots. From the flower, expect acropetal and basipetal succession, the five kinds of aestivation with their examples, the five kinds of placentation, and hypogynous, perigynous and epigynous ovary positions. Mango and coconut as drupes and the apple as a false fruit are near certainties.
Important Facts
| Dicot root system | Taproot, as in mustard and gram |
|---|---|
| Monocot root system | Fibrous, as in wheat and grass |
| Conical, fusiform, napiform roots | Carrot, radish, turnip and beetroot |
| Prop roots | Banyan |
| Stilt roots | Maize, sugarcane and screw pine |
| Pneumatophores | Rhizophora and other mangroves |
| Underground stems | Rhizome in ginger, tuber in potato, bulb in onion, corm in Colocasia |
| Phylloclade and cladode | Opuntia and Euphorbia; Asparagus and Casuarina |
| Venation | Reticulate in dicots, parallel in monocots |
| Phyllotaxy | Alternate in China rose, opposite in guava, whorled in Alstonia |
| Racemose and cymose | Acropetal succession and basipetal succession |
| Aestivation | Valvate in Calotropis, twisted in cotton, imbricate in gulmohar, vexillary in pea |
| Placentation | Marginal in pea, axile in tomato, parietal in mustard, free central in Dianthus, basal in sunflower |
| Drupe and false fruit | Mango and coconut are drupes; apple and pear are false fruits |
Practice MCQs on this topic
Which of the following plants can survive in extremely saline conditions?
- A.Epiphytes
- B.Halophytes
- C.Xerophytes
- D.Hydrophytes
Show answer
Halophytes are plants of saline soils, chiefly the mangroves of tidal creeks and deltas such as Rhizophora and Avicennia, and their morphology is shaped by that habitat: they bear pneumatophores, negatively geotropic breathing roots that rise out of the waterlogged mud, along with stilt and prop roots for support and…
Read the full explanation →The potato is a modification of which plant organ?
- A.Root
- B.Stem
- C.Leaf
- D.Fruit
Show answer
The potato is an underground stem tuber, the swollen tip of an underground branch, and the proof is in its morphology: it bears nodes, the depressions called eyes, and each eye carries an axillary bud that can sprout into a new shoot.
Read the full explanation →The edible part of the carrot is a modified
- A.Conical taproot
- B.Fibrous root
- C.Stem tuber
- D.Adventitious root
Show answer
The carrot stores food in its primary root, which is broad at the top and tapers steadily to a point, and that shape is described as conical.
Read the full explanation →Prop roots, which hang from spreading branches and give them mechanical support, are a familiar feature of which tree?
- A.Maize
- B.Banyan
- C.Screw pine
- D.Rhizophora
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The banyan's horizontal branches grow so long and heavy that they send down thick aerial roots which reach the soil, thicken into pillars and carry the weight of the branch; these are called prop or pillar roots.
Read the full explanation →Pneumatophores, the negatively geotropic breathing roots, are characteristic of
- A.Mangrove plants such as Rhizophora
- B.Desert plants such as Opuntia
- C.Epiphytic orchids such as Vanda
- D.Parasitic plants such as Cuscuta
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The mud of a tidal swamp is waterlogged and almost free of oxygen, so these plants send up roots that grow vertically out of the soil into the air and take in oxygen through pores; such roots grow against gravity and are therefore called negatively geotropic.
Read the full explanation →The flattened, green, leaf-like stem of Opuntia that carries out photosynthesis is called a
- A.Phyllode
- B.Phylloclade
- C.Cladode
- D.Pulvinus
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In Opuntia and in many Euphorbia species the leaves are reduced to spines to cut down transpiration, and the stem takes over photosynthesis by becoming flattened, green and fleshy; such a stem is a phylloclade.
Read the full explanation →Parallel venation in leaves is a characteristic feature of
- A.Dicotyledons
- B.Monocotyledons
- C.Gymnosperms
- D.Pteridophytes
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In a monocot leaf, such as that of wheat, maize, grass, banana or canna, the veins run side by side along the length of the lamina without forming a network, and this parallel venation goes with the other monocot features: one cotyledon in the seed, a fibrous root system, scattered…
Read the full explanation →In a racemose inflorescence, the flowers are borne in
- A.Basipetal succession
- B.Acropetal succession
- C.A single terminal cluster
- D.No definite order
Show answer
In a racemose inflorescence the main axis does not end in a flower but keeps growing, so the lowest flower is the oldest and the youngest buds are at the tip; this upward order is called acropetal, as in radish, mustard and Larkspur.
Read the full explanation →Vexillary aestivation of the corolla is found in the flower of
- A.Pea
- B.Cotton
- C.Calotropis
- D.Gulmohar
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In vexillary or papilionaceous aestivation the corolla has five petals of unequal size: one large posterior petal, the standard, which covers two lateral wing petals, which in turn cover the two smallest anterior petals that are fused into a keel.
Read the full explanation →The apple is regarded as a false fruit because
- A.It has no seeds
- B.It develops from the thalamus along with the ovary
- C.It develops without fertilisation
- D.Its pericarp is stony
Show answer
A true fruit forms from the ovary alone, but in the apple and the pear the thalamus grows, becomes fleshy and forms the greater part of the edible tissue, while the ovary makes only the core; such a fruit is called a false or spurious fruit, and the specific type…
Read the full explanation →Mango and coconut are examples of which type of fruit?
- A.Berry
- B.Drupe
- C.Pome
- D.Legume
Show answer
A drupe is a fleshy fruit with a thin epicarp, a mesocarp that may be pulpy as in the mango or fibrous as in the coconut, and a hard, stony endocarp enclosing a single seed; the coconut's shell is that endocarp and the white kernel is the seed.
Read the full explanation →Marginal placentation, in which the ovules are borne along the fused margin of a single carpel, is found in
- A.Tomato
- B.Pea
- C.Mustard
- D.Sunflower
Show answer
The pea's ovary is made of one carpel whose two margins fuse to form a ridge, and the ovules are arranged in two rows along that ridge; this is marginal placentation, and it is why the pod opens to show a single row of seeds on each side.
Read the full explanation →Frequently Asked Questions
Is the potato a root or a stem?
It is a stem, specifically an underground stem tuber. The proof is morphological: the potato bears nodes, seen as the depressions called eyes, and every eye carries an axillary bud that can sprout. A root has neither nodes nor buds. The sweet potato, by contrast, really is a root, a tuberous adventitious root, and the two are often confused in examinations.
What is the difference between a phylloclade and a phyllode?
A phylloclade is a modified stem: flattened, green and fleshy, taking over photosynthesis when the leaves are reduced to spines, as in Opuntia and Euphorbia. A phyllode is a modified leaf, specifically a flattened green petiole that does the work of a lamina after the lamina has fallen, as in the Australian acacia. A cladode is a phylloclade of one or two internodes only, usually cylindrical, as in Asparagus and Casuarina.
What is the difference between racemose and cymose inflorescence?
In a racemose inflorescence the main axis keeps growing and never ends in a flower, so the oldest flower is the lowest and the order of opening is acropetal, as in radish and mustard. In a cymose inflorescence the main axis ends in a flower, so the oldest flower is at the top and the order is basipetal, as in Solanum and jasmine.
Why is the apple called a false fruit?
Because its fleshy edible part does not come from the ovary. In the apple and the pear the thalamus grows and becomes fleshy around the ovary, while the ovary itself forms only the core that holds the seeds. A fruit formed from the ovary alone is a true fruit; one in which the thalamus or another floral part contributes is a false or spurious fruit, and this particular type is called a pome.
What are pneumatophores and why do mangroves need them?
They are breathing roots that grow vertically upward out of the soil, against gravity, and take in air through pores on their surface. Mangrove plants such as Rhizophora grow in tidal mud that is waterlogged and nearly free of oxygen, so the ordinary underground roots cannot respire. The pneumatophore solves that problem, and it is one of the clearest cases in botany of form following habitat.
