Morphology of Flowering Plants Class 11 Notes

The root system is the underground part of the plant that anchors it, absorbs water and minerals, and stores food. In most dicots the primary root grows deep and branches — this is the tap root system. In most monocots the primary root is short-lived and replaced by a cluster of thin roots — the fibrous root system. Some plants like grass and banyan develop roots from nodes of the stem or even from leaves — these are adventitious roots.

Modifications of the Root

• Storage roots: swollen with food — carrot (conical), turnip (napiform), sweet potato (tuberous).
• Support roots (prop roots): arise from lower stem branches, grow down into soil — e.g. banyan.
• Respiration roots (pneumatophores): vertical roots growing upward in mangroves (Rhizophora) with pores (lenticels) for gas exchange.
• Assimilatory roots: green, perform photosynthesis — e.g. Tinospora.
• Sucking / haustorial roots: penetrate host tissue to absorb nutrients — e.g. Cuscuta (parasitic plant).

The stem is the aerial part that bears leaves, flowers and fruits. It has nodes (points of leaf attachment) and internodes (regions between nodes). Stems can be herbaceous (soft, green) or woody. Underground stems like potato and ginger store food; aerial stems may bear thorns (cactus) or tendrils (grapevine) for support.

Modifications of the Stem

• Runners (stolons): horizontal stems that creep along the ground and root at nodes — e.g. grass, strawberry.
• Tubers: swollen underground stem tips for food storage — e.g. potato. Each eye is a bud.
• Tendrils: thin coiling structures for climbing — e.g. grapevine, pea.
• Bulb: short stem with fleshy leaves — e.g. onion, garlic.
• Corm: short, swollen underground stem — e.g. Colocasia, saffron.
• Phylloclade: flattened, leaf-like photosynthetic stem — e.g. Opuntia.

A leaf is a flat, green, photosynthetic organ that arises from a node. It has a leaf base (petiole in stalked leaves, sheath in grasses), a lamina (blade) and veins. Leaves may be simple (single lamina) or compound (lamina divided into leaflets — pinnate like neem, palmate like silk cotton).

Venation and Phyllotaxy

• Reticulate venation: veins form a network — typical of dicots (mango, peepal).
• Parallel venation: veins run parallel — typical of monocots (grass, maize).
• Alternate phyllotaxy: one leaf per node — mustard, sunflower.
• Opposite: two leaves per node on opposite sides — guava, Calotropis.
• Whorled: more than two leaves at a node — Alstonia.

Modifications of the Leaf

• Tendrils: leaf or leaflet modified for climbing — e.g. pea.
• Spines: defence — e.g. cactus (Opuntia).
• Pitcher: insectivorous — e.g. Nepenthes (pitcher plant).
• Fleshy leaves for storage — e.g. onion, garlic.

A flower is the reproductive shoot. It has four whorls on the thalamus: calyx (sepals — green, protective), corolla (petals — coloured to attract pollinators), androecium (stamens — male, each with anther and filament) and gynoecium (carpels — female, each with stigma, style and ovary). A flower is complete when all four whorls are present, incomplete when any whorl is missing.

Symmetry and Key Terms

• Actinomorphic (radial symmetry): can be divided into equal halves by any plane passing through the centre — e.g. mustard, rose.
• Zygomorphic (bilateral symmetry): can be divided into equal halves by only one plane — e.g. pea, gulmohar.
• Asymmetric: cannot be divided into two equal halves — e.g. cyclamen.
• Cohesion: fusion of similar parts (e.g. stamens united in tubiflorous condition).
• Adhesion: fusion of dissimilar parts (e.g. stamens fused to petals — epipetalous).
• Epiphyllous: stamens attached to petals.

Position of Ovary

• Hypogynous: ovary superior — other whorls below it — e.g. mustard, china rose.
• Perigynous: ovary half-inferior — thalamus forms a cup around it — e.g. peach, rose.
• Epigynous: ovary inferior — other whorls above it — e.g. guava, cucumber, sunflower.

After fertilisation the ovary develops into the fruit. A true fruit develops solely from the ovary — e.g. mango, pea. A false fruit (pome) develops partly from the thalamus — e.g. apple, strawberry. A parthenocarpic fruit develops without fertilisation — e.g. banana, seedless grape.

• Fruit parts: pericarp (fruit wall from ovary wall) which may be fleshy or dry, and seeds.
• Dicot seed: two cotyledons store food; embryo has radicle, plumule and hypocotyl. Endosperm may be present (albuminous — castor) or consumed (non-albuminous — pea).
• Monocot seed: one cotyledon (scutellum in grasses); endosperm present; embryo has coleoptile (shoot tip cover) and coleorhiza (root tip cover). Seed coat is fused with fruit wall (pericarp) in grains.

Example: The root system of wheat is fibrous while that of mustard is tap root. Why does this difference arise?

Solution: Wheat is a monocot — its primary root is short-lived and replaced by many adventitious roots arising from the stem base, giving a fibrous root system. Mustard is a dicot — its radicle grows continuously into a prominent primary root that branches laterally, forming a tap root system. The embryonic type (monocot vs dicot) determines the root architecture.

Example: A flower is described as epigynous with axile placentation. Identify the possible fruit and name one real example.

Solution: In an epigynous flower the ovary is inferior; after fertilisation the fruit wall (pericarp) develops below the attachment of the other floral parts, often with the floral remnants visible on top. Axile placentation means the ovary has multiple chambers with ovules on a central axis. A common example is the tomato (Solanaceae) — it is a berry with many seeds arranged around the central axis.

Exercises (NCERT Q1–Q10)

• 1) How is a pinnately compound leaf different from a palmately compound leaf?
• 2) Explain with suitable examples the different types of phyllotaxy.
• 3) Define the following terms: (a) aestivation (b) placentation (c) actinomorphic (d) zygomorphic (e) superior ovary (f) perigynous flower (g) epipetalous stamen
• 4) Differentiate between (a) Racemose and cymose inflorescence (b) Apocarpous and syncarpous ovary
• 5) Draw the labelled diagram of the following: (i) gram seed (ii) V.S. of maize seed
• 6) Take one flower of the family Solanaceae and write its semi-technical description. Also draw their floral diagram.
• 7) Describe the various types of placentations found in flowering plants.
• 8) What is a flower? Describe the parts of a typical angiosperm flower.
• 9) Define the term inflorescence. Explain the basis for the different types inflorescence in flowering plants.
• 10) Describe the arrangement of floral members in relation to their insertion on thalamus.

Answers at a glance

1. 1
   Q1 → Both are compound leaves, in which the lamina is divided into leaflets separated by gaps, and in both a single axillary bud is present at the base of the whole leaf and never at the base of a leaflet, which is what distinguishes a compound leaf from a lobed simple leaf. They differ in where the leaflets are attached. In a pinnately compound leaf the leaflets are borne on a common elongated axis, the rachis, which is a continuation of the petiole and represents the midrib, and they are arranged along its length in two lateral rows; the rachis may carry a terminal leaflet, in which case the leaf is imparipinnate or odd-pinnate as in neem, or it may not, in which case it is paripinnate as in tamarind, and the examples are neem, Azadirachta indica, tamarind, Tamarindus indica, and rose. In a palmately compound leaf the leaflets are all attached at a single common point at the tip of the petiole, with no rachis between them, and they radiate from that point, so the petiole itself ends in the point of attachment; the examples are the silk cotton tree, Bombax ceiba, and the lupin, Lupinus. Thus the essential difference is the point of leaflet attachment, along a rachis in the pinnate condition and at a single point in the palmate condition.
2. 2
   Q2 → Phyllotaxy is the arrangement of the leaves at the nodes of the stem, and three types are recognised according to the number of leaves arising at each node. In the alternate type a single leaf arises at each node and the leaves are arranged in a spiral around the stem, so each leaf is offset from the one above it, and where they lie in two ranks in a single plane the condition is called distichous; the examples are the China rose, Hibiscus rosa-sinensis, mustard and the sunflower. In the opposite type two leaves arise at each node, at the same level and on opposite sides of the stem, and where successive pairs are set at right angles to one another the arrangement is called decussate, so that pairs at one node stand at right angles to the pairs at the node above and the node below, giving four vertical rows of leaves; the examples are Calotropis, the madar, and the guava. In the whorled type three or more leaves arise at each node and form a whorl around the stem, as in Alstonia scholaris, where there may be six to eight leaves at a node. Thus the classification depends simply on whether one, two, or three or more leaves arise at each node.
3. 3
   Q3 → (a) Aestivation is the arrangement of the sepals and petals in respect to one another in the floral bud, and it may be valvate, twisted, imbricate or vexillary. (b) Placentation is the arrangement of the ovules within the ovary, and it may be basal, marginal, axile, free-central or parietal. (c) Actinomorphic means radially symmetrical, so the flower can be divided into two equal halves by any plane passing through its centre or axis, as in the mustard, the Datura and the chilli. (d) Zygomorphic means bilaterally symmetrical, so the flower can be divided into two similar halves in only one particular vertical plane, as in the pea, the gulmohur, the bean and Cassia. (e) A superior ovary is one in which the gynoecium occupies the highest position while the sepals, petals and stamens are situated below it, as in the mustard, the China rose and the brinjal. (f) A perigynous flower is one in which the gynoecium is situated in the centre and the other parts are located on the rim of the thalamus almost at the same level, so that the ovary is half inferior, as in the plum, the rose and the peach. (g) An epipetalous stamen is one whose filament is attached to the petal, so that it is borne on the corolla, as in the brinjal, the contrasting condition of attachment to the perianth being epiphyllous, as in the flowers of lily.
4. 4
   Q4 → (a) In a racemose inflorescence the apical bud is never used up in producing a flower, so the growth of the main axis is unlimited or indeterminate and continues, the main axis is called the mother of the flowers, the flowers are borne laterally, and they open in an acropetal succession, that is from the base upwards towards the apex, so the youngest are at the apex. In a cymose inflorescence the apical bud is used up in producing a flower, so the growth of the main axis is limited or determinate and further growth occurs only from the lateral buds, giving a monochasial, dichasial or polychasial arrangement, and the flowers are borne in a basipetal order, that is from the apex downwards towards the base, so the oldest are at the apex. The examples of the racemose type are the raceme, spike, catkin, spadix, corymb, umbel and panicle, and of the cymose type the cyme, dichasium, polychasium and the scorpioid and helicoid cymes. (b) In an apocarpous gynoecium the carpels are free and are not fused, so there may be many carpels or only one, and each carpel forms a closed ovary with its own ovules, placenta, style and stigma, as in the lotus and the rose, with Michelia as the single-carpel example. In a syncarpous gynoecium two or more carpels are fused into a single structure with a common ovary, style and stigma, as in the mustard and the tomato, and such an ovary may be unilocular with a false septum, as in the mustard, or multilocular with true septa, or free-central as in Dianthus and Primrose, in which the carpels are fused at the centre but the septa are absent.
5. 5
   Q5 → (i) Gram seed, of Cicer arietinum: draw a small rough angular seed and then its enlarged longitudinal section, and label the seed coat with its two layers, the outer testa and the inner tegmen, the hilum, the scar on the seed coat through which the developing seed was attached to the fruit, the micropyle, the small pore just above the hilum, and the chalaza at the opposite end, the two large cotyledons which fill the entire seed cavity and serve as the storage organ, and the plumule or embryonic shoot and the radicle or embryonic root with the short embryonal axis between them. State in the caption that the gram seed is a non-endospermic dicotyledonous seed, so that the food is stored in the cotyledons. (ii) Vertical section of the maize grain, of Zea mays: label the seed coat and fruit wall, which in this one-seeded fruit are fused and form the outer covering, the bulky endosperm which fills the grain and is the main food-storing tissue, the aleurone layer, the proteinous outer covering of the endosperm which separates the embryo, the scutellum, the single large shield-shaped cotyledon lying in a groove at one end of the endosperm between the endosperm and the embryo and absorbing the endosperm nutrients, the coleoptile enclosing the plumule or developing shoot, and the coleorhiza enclosing the radicle or developing root. State in the caption that the maize grain is a caryopsis and therefore endospermic and monocotyledonous, and that the food is stored in the endosperm rather than in the cotyledon.
6. 6
   Q6 → Solanaceae, the potato family, the illustrated plant being Solanum nigrum, the makoi. Habit: the plants are mostly herbs and shrubs, and rarely small trees, and the family is widely distributed in the tropics, the subtropics and even the temperate zones. Stem: herbaceous and rarely woody, aerial, erect, cylindrical, branched, solid or hollow, hairy or glabrous, with an underground stem in potato, Solanum tuberosum. Leaves: alternate, simple and rarely pinnately compound, exstipulate, with reticulate venation. Inflorescence: solitary, axillary or cymose, as in Solanum. Flower: bisexual and actinomorphic. Calyx: the sepals are five and united, persistent, with valvate aestivation. Corolla: the petals are five and united, with valvate aestivation. Androecium: the stamens are five and epipetalous, that is attached to the corolla. Gynoecium: bicarpellary and obligately placed, syncarpous, the ovary superior and bilocular, with a swollen placenta bearing many ovules and axile placentation. Fruits: a berry or a capsule. Seeds: many and endospermic. The floral formula is Br, with the actinomorphic sign, the bisexual sign, K(5), C(5), A5 and G(2) with a line beneath the G for the superior ovary, brackets marking fusion and a line above the symbols marking adhesion. The floral diagram, drawn from outside inwards, shows a circle for the mother axis, then five united valvate sepals forming the calyx, then five united valvate petals forming the corolla, then five anthers borne on the corolla to show the epipetalous condition, and at the centre the two fused carpels in cross section as a bilocular superior ovary with many ovules on the swollen central placenta in each locule, showing the axile placentation, the style and stigma above.
7. 7
   Q7 → Placentation is the arrangement of the ovules within the ovary, and five types are recognised, the order being from the simplest to the most complex. In basal placentation the placenta develops at the base of the ovary and a single ovule is attached to it, as in the sunflower and the marigold. In marginal placentation the placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge in two rows, the gynoecium being apocarpous and the ovary unilocular, as in the pea. In axile placentation the placenta is axial and the ovules are attached to it in a multilocular ovary, so that the number of locules equals the number of carpels, as in the China rose, the tomato and the lemon. In free-central placentation the ovules are borne on a central axis and the septa are absent, so the ovary is unilocular and the central axis is free in the cavity, as in the Dianthus and the Primrose; this arises by the loss of the septa during development, as is clear in members such as the Nicandra in which the septa persist and the placentation is axile. In parietal placentation the ovules develop on the inner wall or on the peripheral part of the ovary, which is one-chambered but becomes two-chambered due to the formation of a false septum, as in the mustard and in Argemone.
8. 8
   Q8 → A flower is the reproductive unit in the angiosperms, meant for sexual reproduction, and it is a modified shoot in which the leaves are modified, so that the sepals, petals, stamens and carpels are all leaf-like organs. It consists of four whorls borne on the thalamus or receptacle, the swollen end of the stalk or pedicel: the calyx, the corolla, the androecium and the gynoecium. The calyx is the outermost whorl and consists of the sepals, which are generally green and leaf-like and protect the flower in the bud stage; the sepals may be free, polysepalous, or united, gamosepalous, in which case they form a calyx tube. The corolla is the second whorl and consists of the petals, which are usually brightly coloured to attract insects for pollination; the petals may be free, polypetalous, or united, gamopetalous, in which case they form a corolla tube, and the corolla may be tubular, bell-shaped, funnel-shaped or wheel-shaped. The androecium is the third whorl and consists of the stamens, each with a filament and a usually bilobed anther, each lobe having two chambers, the pollen-sacs, in which the pollen grains are produced; a sterile stamen is called a staminode, the stamens may be free, polyandrous, or united into one, two or more bundles, monoadelphous, diadelphous and polyadelphous, and where they are attached to the petals the condition is epipetalous, as in the brinjal, and where to the perianth, epiphyllous, as in lily. The gynoecium is the innermost whorl and the only essential one, since it alone bears the ovules; it consists of one or more carpels, which may be free, apocarpous, as in the lotus and the rose, or fused, syncarpous, as in the mustard and the tomato, and each carpel consists of a stigma to receive the pollen, a style connecting the stigma to the ovary, and an ovary which is the enlarged basal part and bears one or more ovules on a flattened, cushion-like placenta. The calyx and the corolla are accessory organs, while the androecium and the gynoecium are the reproductive organs, and in some flowers such as the lily the calyx and the corolla are not distinct and are together termed the perianth. After fertilisation the ovules develop into seeds and the ovary matures into a fruit.
9. 9
   Q9 → An inflorescence is the arrangement of flowers on the floral axis, and the axis bearing the flowers is the peduncle, while the stalk of an individual flower is the pedicel, and a flower without a pedicel is sessile. When a shoot tip transforms into a flower, that flower is always solitary, since the whole shoot has been converted. Inflorescences are classified first on the behaviour of the main axis. In a racemose type of inflorescence the main axis continues to grow, the flowers are borne laterally, and they open in an acropetal succession from the base upwards towards the apex, so the youngest flowers are at the apex. In a cymose type of inflorescence the main axis terminates in a flower and hence is limited in growth, the flowers are borne in a basipetal order from the apex downwards towards the base, so the oldest flowers are at the apex, and the lateral axes also terminate in a flower; the subtypes are the monochasium, the dichasium and the polychasium, according to the number of lateral axes, and the scorpioid and the helicoid cyme, according to the arrangement of the branches. Within the racemose group the second basis is whether the flowers are pedicellate or sessile, together with the length and shape of the axis: an elongated axis with pedicellate flowers gives a raceme, as in mustard, and with sessile flowers a spike, as in the gladiolus; a very short axis with pedicellate flowers gives an umbel, as in the onion, and a short axis with sessile flowers a head or capitulum, as in the sunflower; a branched raceme gives a panicle; a flat axis with pedicels of unequal length, so that the flowers lie at one level, gives a corymb, as in the candytuft; a spike with a fleshy axis gives a spadix with a spathe, as in the Arum; and a spike with a slender axis and pendulous sessile flowers gives a catkin, as in the mulberry and the oak.
10. 10
    Q10 → The floral members are inserted on the thalamus, or receptacle, which is the swollen end of the floral axis, in a definite arrangement, and the description is decided by the position of the calyx, the corolla and the androecium in respect of the ovary. In the hypogynous flower the gynoecium occupies the highest position while the other parts are situated below it, so the ovary is superior, as in the mustard, the China rose and the brinjal. In the perigynous flower the gynoecium is situated in the centre and the other parts of the flower are located on the rim of the thalamus almost at the same level, so the ovary is half inferior, as in the plum, the rose and the peach. In the epigynous flower the margin of the thalamus grows upward, enclosing the ovary completely and getting fused with it, while the other parts of the flower arise above the ovary, so the ovary is inferior, as in the guava and the cucumber and in the ray florets of the sunflower. The second, related arrangement is the aestivation, the mode of arrangement of the sepals or petals in the floral bud with respect to the other members of the same whorl, and it has four types: valvate, where the members just touch at the margin without overlapping, as in Calotropis; twisted or contorted, where one margin of each member regularly overlaps that of the next, as in the china rose, the lady’s finger and the cotton; imbricate, where the margins overlap without any particular direction, as in Cassia and the gulmohur; and vexillary or papilionaceous, where the largest standard petal overlaps the two lateral wings, which in turn overlap the two smallest anterior keel petals, giving the butterfly-like corolla of the pea and the bean.

MCQ Questions

1 Mark Questions

1. 1
   What is phyllotaxy? (Ans: the arrangement of leaves on the stem)
2. 2
   Give one example of a modified root for storage. (Ans: carrot, radish, sweet potato)
3. 3
   Which type of venation is found in monocot leaves? (Ans: parallel)
4. 4
   Sepals and petals of a flower are collectively called what? (Ans: calyx and corolla — the perianth when similar)

2 Mark Questions

1. 1
   Differentiate between racemose and cymose inflorescence with one example each.
2. 2
   Give two functions of roots and two functions of stems.
3. 3
   What are haustoria? Give an example. (Ans: parasitic roots that absorb nutrients, e.g. in the dodder (Cuscuta))

3 Mark Questions

1. 1
   Describe the structure of a typical flower mentioning its four whorls and the fusion of stamens and carpels.
2. 2
   Explain the modification of stems with suitable examples. (Ans: storage (rhizome, tuber, bulb, corm), support (tendril), protection (thorns), photosynthesis (phylloclade))
3. 3
   Describe the types of aestivation found in the corolla with one example each. (Ans: valvate, twisted, imbricate, vexillary — Calotropis, cotton/China rose, peal of Cassia, pea)

5 Mark Questions

1. 1
   Give the regions of the root in sequence and describe the function of each region with a labelled description. (Ans: root cap, meristematic zone, zone of elongation, zone of maturation/hairs)
2. 2
   Describe the types of inflorescence, giving the difference between determinate and indeterminate axes and one example of each type. (Ans: racemose (radish, chinarose), cymose (Dianthus), special — cyathium, hypanthodium, verticillaster)