Floral Diversity

(d) Phycology

The statement describes a disease caused by an alga (Cephaleuros virescens), and phycology is the branch of biology that deals with the study of algae.

Five characteristics of Chlorophyceae (green algae):

1. Grass-green colour. The thallus is grass-green due to the dominance of chlorophyll a and chlorophyll b, which are present in the same proportion as in higher plants. The green colour is masked only rarely, as in Trentepohlia, where haematochrome (a red pigment) accumulates.

2. Stored food is starch. Photosynthate is stored as starch, deposited inside the chloroplast around the pyrenoids. In some members (e.g. Trebouxia) oil droplets may also occur.

3. Chloroplast with pyrenoids. The chloroplast is well organised and of varied shape — cup-shaped (Chlamydomonas), girdle-shaped (Ulothrix), star-shaped (Zygnema), or reticulate (Oedogonium) — and typically bears one or more pyrenoids.

4. Cell wall of cellulose. The cell wall is made mainly of cellulose, often with pectin; in Chara it is encrusted with calcium carbonate. The flagella, when present, are of the whiplash type and usually two to many in number.

5. Wide range of thallus and modes of reproduction. The plant body ranges from unicellular motile (Chlamydomonas), colonial (Volvox), filamentous (Spirogyra), to multicellular parenchymatous forms (Ulva). Reproduction is by vegetative, asexual (zoospores, aplanospores) and sexual methods — isogamous, anisogamous or oogamous — with isogamy being the most common.

Gymnosperms are more advanced than pteridophytes — five points:

1. Seed formation (most important advance): Gymnosperms are seed-bearing plants (spermatophytes); the ovule after fertilisation becomes a seed. Pteridophytes have no seeds — they reproduce only by spores. Seeds protect the embryo and supply stored food, giving a clear survival advantage on land.

2. Heterospory and embryo protection: In gymnosperms the megaspore is retained inside the ovule on the parent plant, where the female gametophyte and embryo develop. In pteridophytes the spore is shed and the gametophyte (prothallus) leads a free-living, independent existence, so the embryo has no such protection.

3. Independence from water for fertilisation: Gymnosperms are siphonogamous — the pollen tube carries the male gametes to the egg, so water is not needed for fertilisation. Pteridophytes are dependent on a film of water for the motile, flagellated antherozoids to swim to the archegonium (except a few aquatic forms).

4. Sporophyte dominance and vascular tissue: In both groups the sporophyte is dominant and has true vascular tissue (xylem and tracheids, phloem), but in gymnosperms the sporophyte is a large, woody, long-lived tree with well-developed secondary growth. Pteridophytes are mostly small, herbaceous, and lack true secondary growth.

5. Seed habit and dispersal: The seed habit allows the embryo to be dispersed and to remain dormant until conditions are favourable. Pteridophytes lack this; their spores are delicate and must germinate immediately in a moist habitat, restricting them to damp, shady places.

Conclusion: Because of seeds, retention of the embryo in the ovule, pollen-tube fertilisation, and a dominant woody sporophyte, gymnosperms are placed above pteridophytes in the plant kingdom.

Comparison between simple fruit and multiple fruit (2 points)

Role of fruit in continuity of generation

1. Protection of seeds — The fruit wall (pericarp) encloses the seeds and protects them from mechanical injury, unfavourable weather, insects and pathogens, so that the seeds remain viable until favourable conditions arrive.

2. Nourishment of the embryo — The fruit provides food and a suitable internal environment for the developing embryo, helping it mature into a healthy seed capable of germination.

3. Aid in dispersal of seeds — Fruits help scatter seeds to distant places, reducing competition and overcrowding. Succulent fruits are eaten by animals and birds, and the resistant seeds pass out undigested with droppings; dry fruits with wings, hairs or hooks are carried by wind or attach to animal bodies; some fruits burst and throw seeds away. Coconut and other fibrous fruits float and are carried by water.

4. Protection during unfavourable period — The hard seed coat and the fruit covering keep the seed dormant and safe through drought or cold, so germination occurs only when conditions are suitable.

By thus protecting the seeds, nourishing the embryo and ensuring wide dispersal, the fruit guarantees that seeds reach new habitats and germinate into new plants, thereby maintaining the continuity of the species from one generation to the next.

Diagnostic floral characters of family Solanaceae

1. Habit: Mostly herbs and shrubs, a few small trees (e.g. Solanum, Datura, Capsicum).
2. Inflorescence: Solitary or cymose, axillary or extra-axillary.
3. Flower: Bracteate or ebracteate, pedicellate, complete, bisexual, actinomorphic, pentamerous and hypogynous.
4. Calyx: 5 sepals, gamosepalous, persistent (often enlarging in the fruit as in Physalis), valvate or imbricate.
5. Corolla: 5 petals, gamopetalous, rotate, funnel-shaped or campanulate, with valvate or twisted aestivation.
6. Androecium: 5 stamens, epipetalous, alternating with the corolla lobes (alternipetalous); anthers dithecous, dehiscing by longitudinal slits or apical pores.
7. Gynoecium: Bicarpellary, syncarpous, ovary superior, bilocular (a false septum makes it four-locular in Datura); axile placentation with many ovules; style simple, stigma capitate or bifid.
8. Fruit and seed: Berry (tomato, brinjal) or capsule (Datura); seeds endospermic.

Floral formula

$\text{Br}\ \oplus\ \text{⚥}\ K_{(5)}\ C_{(5)}\ A_{5}\ \underline{G}_{(2)}$

Here Br = bracteate, $\oplus$ = actinomorphic, ⚥ = bisexual, $K_{(5)}$ = five fused sepals, $C_{(5)}$ = five fused petals, $A_5$ = five stamens attached to the petals (epipetalous), and $\underline{G}_{(2)}$ = two fused carpels with a superior ovary.

Floral diagram

Draw a circle with the mother axis at the top and the bract at the bottom. From outside to inside show:

• Five sepals, fused at the base (outermost whorl).
• Five fused petals alternating with the sepals.
• Five stamens placed opposite the gaps between petals and joined to the corolla tube.
• At the centre, a two-chambered (bilocular) ovary with the ovules on a central axis (axile placentation), the two carpels placed obliquely.

Plants of the family

(b) Bryophytes

Bryophytes live on land but need water for the swimming male gametes to reach the egg, so they depend on water for fertilisation like amphibians.

(b) Zea mays

Maize belongs to family Poaceae. Oryza sativa is rice, Triticum aestivum is wheat and Solanum tuberosum is potato.

(b) Mycorrhiza

In mycorrhiza the fungal hyphae help the plant absorb water and minerals, especially phosphorus, while the plant supplies sugars to the fungus. Lichen is an association of fungus with alga or cyanobacterium.

(b) Radial and polyarch

In roots xylem and phloem lie on separate radii (radial arrangement). Monocot roots have many (more than six) xylem bundles, so they are polyarch.

(c) Compositae (Asteraceae)

In syngenesious stamens the anthers are united into a tube while the filaments remain free, as in sunflower. Cruciferae has tetradynamous stamens and Leguminosae often diadelphous ones.

(c) Parietal

In parietal placentation the ovules are attached to the ovary wall (or its projecting ridges) in a one-chambered, syncarpous ovary, as in mustard and cucumber.

Five general characteristics of Bryophyta

1. Habitat: They are small, simple land plants that grow in moist, shady places; they are called the "amphibians of the plant kingdom" because they need water for fertilisation.
2. Plant body: It is a thallus or a leafy stem-like structure with no true root, stem or leaf; root-like rhizoids anchor the plant.
3. No vascular tissue: Xylem and phloem are absent, so transport is by diffusion.
4. Dominant gametophyte: The main plant body is the haploid gametophyte, which bears sex organs (antheridia and archegonia). The sporophyte depends on it for nutrition.
5. Reproduction: Asexual reproduction is by fragmentation or gemmae; sexual reproduction is oogamous. The biflagellate male gametes swim in water to the egg, and the zygote develops into a sporophyte (foot, seta, capsule) that produces spores. Examples: Marchantia, Funaria, Anthoceros.

Five distinguishing characters of angiosperms

1. Flowers: The reproductive organs are flowers, which are absent in other plant groups.
2. Ovules enclosed in an ovary: Ovules are protected inside the ovary of the carpel, so the seeds are enclosed in a fruit (hence "covered seeds").
3. Fruit formation: After fertilisation the ovary becomes the fruit and the ovules become seeds.
4. Double fertilisation and triploid endosperm: One male gamete fuses with the egg (forming the zygote) and the other with the two polar nuclei (forming the triploid endosperm, $3n$).
5. Advanced vascular tissue: Xylem has vessels and phloem has companion cells; also they show wide habit variation and are divided into dicots and monocots.

Placentation

Placentation is the arrangement of ovules on the placenta inside the ovary. The main types are:

1. Marginal: The placenta lies along the ventral suture of a one-chambered (monocarpellary) ovary. Example: pea, bean.
2. Axile: The ovary is multilocular and the placenta is in the centre where the septa meet. Example: China rose (Hibiscus), tomato, lemon.
3. Parietal: The ovary is one-chambered (or falsely divided) and the ovules are on the inner wall of the ovary. Example: mustard, cucumber, Argemone.
4. Free central: The ovary is unilocular and the ovules are borne on a central axis without septa. Example: Dianthus, primrose.
5. Basal: The placenta is at the base of a unilocular ovary and bears a single ovule. Example: sunflower, marigold.
6. Superficial: The ovules cover the inner surface of the septa in a multilocular ovary. Example: water lily (Nymphaea).

Wind-pollinated and insect-pollinated flowers

Gymnosperms and angiosperms

Economic importance of fungi

Beneficial effects (four)

1. Food: Mushrooms (Agaricus, morels) are eaten; yeast is used in making bread, and in baking.
2. Fermentation: Yeast (Saccharomyces) ferments sugar to alcohol in brewing and wine making.
3. Medicine: Penicillium gives the antibiotic penicillin; other fungi yield ergot alkaloids and cyclosporine.
4. Decomposers and soil fertility: Saprophytic fungi break down dead matter, recycle nutrients and form mycorrhiza that help plant roots absorb minerals. (Cheese ripening by Penicillium and industrial citric acid production by Aspergillus are further uses.)

Harmful effect (one)

• Plant and human diseases: Fungi cause crop diseases like wheat rust (Puccinia), potato late blight, and smut, and human diseases such as ringworm and athlete's foot. Some, such as Aspergillus flavus, produce toxic aflatoxins in stored food.

Why pteridophytes are called vascular cryptogams

• Vascular: The sporophyte (main plant body) has well-developed vascular tissues, xylem and phloem, for conduction of water and food. Bryophytes lack these tissues.
• Cryptogams: "Cryptogam" means hidden reproduction. Pteridophytes do not produce flowers or seeds; they reproduce by spores, and their sex organs (antheridia, archegonia) are small and hidden on the inconspicuous prothallus.

Since they are non-flowering, seedless plants with vascular tissue, they are called vascular cryptogams (e.g. Dryopteris, Selaginella, Equisetum).

General characters of gymnosperms (e.g. Pinus)

1. They are mostly perennial woody trees or shrubs, and the plant body is a sporophyte differentiated into root, stem and leaves.
2. Roots are usually tap roots, often with mycorrhiza; leaves may be needle-like (Pinus) or pinnate (Cycas) with thick cuticle, sunken stomata, adapted to reduce water loss.
3. Vascular tissue has tracheids (no vessels) in xylem and sieve cells (no companion cells) in phloem.
4. They are heterosporous; microspores and megaspores are produced in male and female cones or strobili.
5. Ovules are naked, borne on megasporophylls, with no ovary or fruit.
6. Pollination is by wind; the pollen tube carries the male gametes (siphonogamy), and the seeds are naked.

Economic importance

• Timber and wood: Pinus, Cedrus and Abies give softwood for furniture, construction and plywood.
• Paper and pulp: Conifer wood is used for paper.
• Resin and turpentine: Pinus yields resin, turpentine and rosin.
• Food and medicine: Seeds of chilgoza pine (Pinus gerardiana) are edible; Ephedra gives ephedrine, used in treating asthma. Cycas stem gives sago starch.
• Ornamental and soil protection: Conifers like Cupressus are planted as ornamentals and for afforestation.

Megasporophyll of Cycas

Diagram (to be drawn): a flat, leaf-like, pinnate megasporophyll with a stalk at the base. Label the rachis (stalk), the sterile pinnate apical portion, and the ovules (two to six) on both sides of the lower fertile part, with the micropyle of each ovule.

Explanation

• Cycas is dioecious; the female plant has no compact female cone. Instead the megasporophylls form a loose rosette at the apex of the stem, around the growing point, alternating with scale leaves.
• Each megasporophyll is a modified leaf, about 15-30 cm long, brown and covered with hairs (a primitive feature).
• The upper part is pinnately cut and sterile; the lower part is narrow and bears 2-6 large, naked ovules on its margins.
• Each ovule has a single integument surrounding the nucellus, with a micropyle through which pollen enters. After fertilisation the ovule becomes a seed, often orange-red and fleshy.

Racemose inflorescence

In racemose inflorescence the main axis keeps on growing and bears flowers laterally in acropetal succession, with the youngest flowers at the apex and the oldest at the base. The types are:

1. Raceme: An elongated axis with stalked (pedicellate) flowers. Example: mustard, radish.
2. Spike: The axis is long but the flowers are sessile. Example: Achyranthes.
3. Spikelet: A small spike of grasses with sessile flowers and glumes. Example: wheat, rice.
4. Catkin: A drooping spike with unisexual flowers. Example: mulberry (male), oak.
5. Spadix: A fleshy spike with sessile flowers, usually surrounded by a large bract (spathe). Example: maize (female), banana, Colocasia.
6. Corymb: The lower flower stalks are longer, so all flowers reach nearly the same level. Example: candytuft, Iberis.
7. Umbel: The flowers have stalks of equal length, arising from a common point. Example: coriander, onion.
8. Capitulum (head): The axis is flattened into a receptacle bearing sessile florets (ray and disc). Example: sunflower, marigold.

Diagrams (to be drawn): a simple line sketch of each type showing the main axis and the flower arrangement.

Internal structure of a monocot root (e.g. maize, 5 marks)

A transverse section (T.S.) of a monocot root shows the following tissues from outside to inside.

1. Epiblema (rhizodermis): single outer layer of thin-walled cells without cuticle or stomata. Many cells give rise to unicellular root hairs that absorb water and minerals.
2. Cortex: wide zone of thin-walled parenchyma with intercellular spaces, storing food. Its innermost layer is the endodermis, a single barrel-shaped layer with Casparian strips on radial and inner tangential walls. Opposite the protoxylem, thin-walled passage cells allow water to enter the stele.
3. Pericycle: single layer of parenchyma just inside the endodermis. It gives rise to lateral roots.
4. Vascular bundles: radial, with xylem and phloem on separate radii, alternating with each other. The xylem is polyarch (usually more than six groups) and exarch (protoxylem towards the periphery, metaxylem towards the centre). Phloem lies in patches between the xylem arms.
5. Conjunctive tissue: parenchyma between xylem and phloem. There is no cambium, so no secondary growth.
6. Pith: large, well developed, central parenchymatous region.

 Epiblema (root hair)
   Cortex (parenchyma)
     Endodermis (Casparian strip, passage cells)
       Pericycle
         Xylem (polyarch, exarch) | Phloem
           Conjunctive tissue
             Large pith

Key identifying features: polyarch xylem, large pith, absence of cambium and of secondary growth.

Family Fabaceae (Leguminosae; sub-family Papilionoideae) (8 marks)

Vegetative characters: herbs, shrubs or trees; leaves alternate, usually pinnately compound (sometimes trifoliate), with stipules and a swollen leaf base (pulvinus). Root nodules contain nitrogen-fixing Rhizobium.

Floral characters (diagnostic):

1. Inflorescence: raceme (sometimes solitary).
2. Flower: bracteate, pedicellate, bisexual, zygomorphic, hypogynous (perigynous in some).
3. Calyx: 5 sepals, gamosepalous, odd sepal anterior, valvate or imbricate.
4. Corolla: 5 petals, polypetalous, papilionaceous: one large posterior standard (vexillum), two lateral wings (alae) and two anterior petals fused into the keel (carina). Aestivation is vexillary (descending imbricate).
5. Androecium: 10 stamens, usually diadelphous (9)+1, sometimes monadelphous or free; anthers dithecous, basifixed.
6. Gynoecium: monocarpellary, unilocular, superior ovary with many ovules on marginal placentation; style bent, stigma simple.
7. Fruit: legume (pod), dehiscing along both sutures. Seed: non-endospermic.

Floral formula: $\%\ \ \text{K}_{(5)}\ \text{C}_{5}\ \text{A}_{(9)+1}\ \underline{\text{G}}_{1}$ (Br, % = zygomorphic, ⚥ = bisexual, underlined G = superior ovary.)

Floral diagram: shows, in a circle viewed from above, the mother axis at the top, bract below, 5 sepals joined at the base, 5 petals (standard outermost at the back, two wings, two keel petals in front), 10 stamens (9 fused in a tube plus one free) and a single central carpel with marginal ovules.

Economically important plants:

1. Pisum sativum (pea) – edible seeds and pods (pulse/vegetable).
2. Glycine max (soybean) – protein-rich seeds and edible oil. (Others: Arachis hypogaea – groundnut; Cicer arietinum – gram; Lens culinaris – lentil.)

Family Cruciferae (Brassicaceae) – semi-technical description (8 marks)

Habit and vegetative characters: mostly annual or biennial herbs, often with pungent watery sap (mustard oil glycosides). Root is a tap root (swollen in radish and turnip). Leaves are alternate, simple, often lobed or lyrate, exstipulate.

Floral characters (diagnostic):

1. Inflorescence: raceme (corymbose), ebracteate.
2. Flower: pedicellate, bisexual, actinomorphic, tetramerous, hypogynous.
3. Calyx: 4 sepals in two whorls of 2 (decussate), polysepalous, often with the inner pair slightly pouched.
4. Corolla: 4 petals arranged in the form of a cross (hence "Cruciferae"), polypetalous, clawed, with imbricate aestivation.
5. Androecium: 6 stamens, tetradynamous (2 short outer, 4 long inner), polyandrous; nectar glands at the base.
6. Gynoecium: bicarpellary, syncarpous, unilocular but divided into two chambers by a false septum (replum); superior ovary, parietal placentation, many ovules.
7. Fruit: siliqua (long) or silicula (short). Seeds are non-endospermic.

Floral formula: $\oplus\ \ \text{K}_{2+2}\ \text{C}_{4}\ \text{A}_{2+4}\ \underline{\text{G}}_{(2)}$ (Br, ⚥, actinomorphic).

Floral diagram: mother axis on top, bract absent; four sepals in two pairs, four petals diagonally alternating with them to form a cross, six stamens (two outer short, four inner long) and a central bicarpellary ovary with parietal placentation and a false septum.

Economically important plants:

1. Brassica campestris (mustard/rapeseed) – oil seed.
2. Brassica oleracea var. capitata (cabbage) – vegetable.
3. Raphanus sativus (radish) – root vegetable. (Others: Brassica rapa – turnip; Capsella bursa-pastoris – a common weed.)

Family Solanaceae – technical description (8 marks)

Habit: herbs, shrubs, a few small trees; stem herbaceous or woody, sometimes with prickles. Leaves: alternate, simple, exstipulate, reticulate venation. Root: tap root.

Inflorescence: solitary axillary, cymose or racemose (often extra-axillary).

Flower: bracteate or ebracteate, pedicellate, complete, bisexual, actinomorphic (zygomorphic in a few), pentamerous, hypogynous.

Calyx: 5 sepals, gamosepalous, persistent (often enlarging in fruit, as in Physalis), valvate or imbricate.

Corolla: 5 petals, gamopetalous, rotate (potato, tomato) or funnel/bell-shaped (Datura), valvate or plicate aestivation.

Androecium: 5 stamens, epipetalous, polyandrous, alternate with the petals (epipetalous and alternipetalous); anthers dithecous, often dehiscing by apical pores (tomato).

Gynoecium: bicarpellary, syncarpous, obliquely placed (carpels not in the median plane); superior ovary, bilocular (becomes falsely 4-locular in Datura), many ovules on swollen axile placentae; style simple, stigma bilobed.

Fruit: berry (tomato, brinjal) or capsule (Datura). Seeds: endospermic.

Floral formula: $\oplus\ \ \text{K}_{(5)}\ \text{C}_{(5)}\ \text{A}_{5}\ \underline{\text{G}}_{(2)}$ (Br, ⚥, actinomorphic, epipetalous stamens).

Floral diagram: bract and mother axis shown; five joined sepals; five joined petals; five stamens attached to the corolla tube and alternating with its lobes; at the centre, a two-chambered ovary placed obliquely with axile placentation.

Economic importance: food (Solanum tuberosum – potato, Solanum lycopersicum – tomato, Solanum melongena – brinjal, Capsicum annuum – chilli); drugs (Atropa belladonna, Datura); Nicotiana tabacum – tobacco.