Fossil Angiosperms & Angiosperm Taxonomy BBO3T06

Syllabus topics (official RTMNU)

1. Origin of Angiosperms: (Bennettitalean theory)
2. Phylogeny of Angiosperm: Homology, monophyly, polyphyly, Clads
3. Fossil angiosperms: Flower (Sahnianthus), Fruit (Enigmocarpon)
4. Angiosperm Taxonomy: Floras, Herbarium, Keys (Indented and Bracketed)
5. Botanical Nomenclature: Principles (Rank and ending of taxa, Principle of priority)

Origin of Angiosperms: (Bennettitalean theory)

Angiosperms (flowering plants) are seed plants whose ovules are enclosed in an ovary. They appear suddenly and in great variety in the Lower Cretaceous (about 130 million years ago). Darwin called their sudden appearance an "abominable mystery". Several theories try to explain their ancestors; the Bennettitalean (Anthostrobilus) theory is the most discussed one in the syllabus.

Bennettitalean / Anthostrobilus theory – proposed by Arber and Parkin (1907). According to it, angiosperms arose from the extinct gymnosperm order Bennettitales (Cycadeoidales) of the Mesozoic era, e.g. Cycadeoidea and Williamsonia.

• Bennettitales had a bisexual strobilus (Cycadeoidea) with sterile perianth-like bracts outside, microsporophylls in the middle and ovules on a central receptacle – the same arrangement as an angiosperm flower (perianth → stamens → carpels).
• Arber and Parkin called this hypothetical ancestor the "Pro-anthostrobilus", which changed into the "Eu-anthostrobilus" (the true flower) of primitive angiosperms like Magnolia.
• The open megasporophylls folded along the midrib to enclose ovules and became carpels; microsporophylls were reduced to stamens.
• Ranales (Magnoliales) are therefore considered the most primitive living angiosperms.

Evidence in favour: bisexual strobilus, spiral arrangement of parts, elongated receptacle, dicot-like seeds with two cotyledons, almost exalbuminous seeds.

Objections: (1) In Bennettitales the ovules are borne on stalks between interseminal scales, not on folded sporophylls, so a carpel cannot be derived easily. (2) Microsporophylls were large, pinnate and fused at the base – very different from stamens. (3) Bennettitales had syndetocheilic stomata while many primitive angiosperms show other types. (4) The group appears at almost the same time as angiosperms, so it is better treated as a parallel line, not a direct ancestor.

Phylogeny of Angiosperm: Homology, monophyly, polyphyly, Clads

Phylogeny is the evolutionary history of a group of organisms. Phylogenetic classification tries to place related plants together on the basis of common descent.

• Homology – similarity due to common ancestry. Homologous structures have the same origin but may differ in function, e.g. tendril of pea (leaflet) and spine of Opuntia (leaf) are both modified leaves. Opposite term: analogy (same function, different origin), e.g. tendril of pea (leaf) and tendril of Passiflora (stem). Only homologous characters are useful in phylogeny.
• Monophyly – a group is monophyletic when all its members come from a single common ancestor. Most botanists (Hutchinson, Takhtajan, Cronquist) consider angiosperms monophyletic, because of shared unique features such as double fertilization, triploid endosperm, 8-nucleate embryo sac, sieve tubes with companion cells and carpels.
• Polyphyly – a group derived from two or more different ancestors. Some workers (e.g. Meeuse) suggested angiosperms arose from several gymnosperm lines; Lam (1948) treated them as diphyletic, and dicots and monocots were also once thought to have separate origins.
• Paraphyly – group having a common ancestor but not including all its descendants (e.g. "dicots" in the old sense).
• Clade – a monophyletic group consisting of an ancestor and all its descendants. A branching diagram showing clades is a cladogram. Cladistics (Willi Hennig, 1950) groups organisms on shared derived characters (synapomorphies), not on primitive characters (plesiomorphies). APG classification of angiosperms is based on clades (e.g. eudicots, monocots, rosids, asterids).

Fossil angiosperms: Flower (Sahnianthus), Fruit (Enigmocarpon)

Both are petrified fossils from the Deccan Intertrappean beds (Upper Cretaceous–Lower Eocene) of Mohgaon Kalan, Chhindwara district (M.P.), near Nagpur.

Sahnianthus (fossil flower) – described by Shukla (1944), named after Prof. Birbal Sahni.

• Flower small, bisexual, actinomorphic, pentamerous, epigynous to perigynous.
• Calyx tube (hypanthium) gamosepalous with 5 lobes; petals 5, free.
• Stamens about 10, in two whorls; anthers dithecous with pollen grains.
• Ovary bilocular with axile placentation and several ovules.
• Shows affinity with family Lythraceae.

Enigmocarpon parijai (fossil fruit) – described by Sahni (1943); the name means "enigmatic fruit".

• Fruit capsule-like, oval, about 1 cm long with a persistent calyx.
• Ovary multilocular (6–8 locules), axile placentation, seeds many per locule.
• Seeds are anatropous with a thick seed coat; loculi separated by thin septa.
• Its affinity is with Lythraceae (some workers compare it with Sonneratiaceae).

Angiosperm Taxonomy: Floras, Herbarium, Keys (Indented and Bracketed)

Taxonomy = identification, nomenclature and classification of plants. Its main tools are floras, herbaria and keys.

Flora – a book listing and describing the plants of a particular area, with keys, descriptions, distribution and flowering time. Examples: Flora of British India (J.D. Hooker, 7 volumes), Flora of Nagpur District, Flora of Maharashtra (BSI). Types: local flora, regional flora, national flora.

Herbarium – a store-house of pressed, dried plant specimens mounted on sheets (standard size about 42 × 29 cm), labelled and arranged in a system (usually Bentham & Hooker in India).

• Steps: collection → pressing and drying → poisoning (HgCl₂ / naphthalene) → mounting → labelling (name, family, locality, date, collector, field number) → storing in cabinets.
• Uses: identification by comparison, record of flora, type specimens, teaching and research.
• Famous herbaria: Royal Botanic Gardens, Kew (largest); Central National Herbarium, Howrah (Kolkata).

Taxonomic key – a device for identification based on pairs of contrasting characters (couplets); such keys are called dichotomous keys.

Example (indented):
1. Leaves with parallel venation ........ Monocot
1. Leaves with reticulate venation
  2. Petals free ........ Polypetalae
  2. Petals fused ........ Gamopetalae

Example (bracketed):
1a. Leaves with parallel venation ........ Monocot
1b. Leaves with reticulate venation ........ 2
2a. Petals free ........ Polypetalae
2b. Petals fused ........ Gamopetalae

Botanical Nomenclature: Principles (Rank and ending of taxa, Principle of priority)

Plant names are governed by the International Code of Nomenclature for algae, fungi and plants (ICN). Its six principles: (1) botanical names are independent of zoological names, (2) application of names is decided by type, (3) nomenclature is based on priority of publication, (4) each taxon has only one correct name, (5) names are in Latin, (6) rules are retroactive.

Principle of priority – the correct name of a taxon is the earliest validly published name. Starting point for vascular plants: Linnaeus' Species Plantarum, 1 May 1753. Later names for the same taxon become synonyms. Priority applies up to the rank of family. Exceptions: nomina conservanda (conserved names) – eight families have alternative names allowed, e.g. Leguminosae = Fabaceae, Cruciferae = Brassicaceae, Compositae = Asteraceae, Gramineae = Poaceae.

5 likely exam questions

Long answer

1. Describe the Bennettitalean (Anthostrobilus) theory of origin of angiosperms. Give evidences in its favour and objections against it.
2. What is a herbarium? Describe the techniques of herbarium preparation and its importance. Add a note on indented and bracketed keys.

Short answer / short notes

3. Describe the fossil flower Sahnianthus with a labelled diagram.
4. Explain the principle of priority in botanical nomenclature.
5. Distinguish between monophyly and polyphyly, and define a clade.

Syllabus topics (official RTMNU)

1. Modern trends in taxonomy: Cytotaxonomy (Karyotype), Phytochemistry (Proteins, Flavonoids and Betalains), Taximetrics to taxonomy (OTUs).
2. Classification of angiosperms: Natural, Artificial and Phylogenetic system of classification.
3. Systems of classification: Bentham & Hooker and Engler & Prantl (Outline only along with merits and demerits)

Modern trends in taxonomy: Cytotaxonomy (Karyotype), Phytochemistry (Proteins, Flavonoids and Betalains), Taximetrics to taxonomy (OTUs).

Classical taxonomy is based mainly on morphology. Modern taxonomy (experimental or biosystematics) adds evidence from cytology, chemistry, anatomy, embryology, palynology and statistics to solve doubtful relationships.

1. Cytotaxonomy – use of chromosome characters in classification.

• Karyotype – the complete set of chromosomes of a species described by their number, size, shape, position of centromere, secondary constrictions and satellites. Its diagrammatic representation (chromosomes arranged in decreasing size) is an idiogram.
• Chromosome number: basic number (x) and polyploidy help to separate species, e.g. Triticum series 2n = 14, 28, 42 (x = 7).
• Symmetric karyotype (chromosomes of similar size, median centromeres) is primitive; asymmetric karyotype is advanced (Stebbins).
• Example uses: separation of Yucca and Agave (bimodal karyotype, 5 large + 25 small chromosomes) from Liliaceae/Amaryllidaceae into Agavaceae; placing Paeonia in its own family Paeoniaceae (x = 5).
• Chromosome behaviour at meiosis (pairing in hybrids) shows genome similarity.

2. Phytochemistry (Chemotaxonomy) – use of chemical constituents in classification.

• Proteins – called semantides (information-carrying molecules). Seed proteins are compared by electrophoresis and serology (antigen–antibody reaction). Similar protein bands = close relationship. Amino acid sequence of cytochrome c is also used.
• Flavonoids – phenolic compounds (flavones, flavonols, anthocyanins). Stable, easily detected by paper chromatography; used at genus and species level, e.g. in identifying hybrids of Baptisia.
• Betalains – nitrogen-containing red (betacyanins) and yellow (betaxanthins) pigments found only in the order Centrospermae (Caryophyllales), e.g. beet (Beta vulgaris), Amaranthus, Bougainvillea, cacti. Betalains and anthocyanins never occur together. Families Caryophyllaceae and Molluginaceae have anthocyanins, so they are separated within the order.

3. Taximetrics (Numerical taxonomy) – classification by numerical methods; developed by Sneath and Sokal (1963) based on the ideas of Adanson (Adansonian principle: all characters given equal weight).

• OTU (Operational Taxonomic Unit) – the basic unit being compared (a specimen, species or genus).
• Steps: choose OTUs → select many characters (at least 60) → code characters (+/–, 1/0) → make a data matrix (OTU × character) → calculate coefficient of similarity → cluster analysis → draw a phenogram (dendrogram).
• Similarity coefficient S = (number of characters matching ÷ total characters compared) × 100.
• Merits: objective, repeatable, uses computers, handles large data. Demerits: needs a lot of data; equal weighting ignores evolutionary importance; phenetic rather than phylogenetic.

Classification of angiosperms: Natural, Artificial and Phylogenetic system of classification.

• Artificial system – Linnaeus (Species Plantarum, 1753) grouped plants by number, union and length of stamens, e.g. Monandria (1 stamen), Diandria (2 stamens). Easy for identification but unnatural (e.g. monocots and dicots mixed).
• Natural system – considers all available characters and groups plants by natural affinity. Best example: Bentham & Hooker's Genera Plantarum.
• Phylogenetic system – arranges plants from primitive to advanced to show evolution. Engler & Prantl started with simple, unisexual, apetalous flowers; Bessey and Hutchinson started with Ranales (Magnolia-type flowers).

Systems of classification: Bentham & Hooker and Engler & Prantl (Outline only along with merits and demerits)

Bentham & Hooker's system – natural system published in Genera Plantarum (3 volumes, 1862–1883) by George Bentham and Joseph Dalton Hooker. Includes 202 families of seed plants (97,205 species).

Outline: Phanerogams (seed plants) divided into three classes:

1. Dicotyledons – 3 subclasses:
   • Polypetalae (petals free) – series Thalamiflorae, Disciflorae, Calyciflorae
   • Gamopetalae (petals fused) – series Inferae, Heteromerae, Bicarpellatae
   • Monochlamydeae (one whorl of perianth) – 8 series
2. Gymnospermae – placed between dicots and monocots
3. Monocotyledons – 7 series (e.g. Microspermae, Epigynae, Coronarieae, Glumaceae)

Merits: based on actual study of specimens at Kew; descriptions are accurate; easy to use for identification; begins with Ranales (now regarded primitive); dicots placed before monocots; followed in most Indian herbaria and floras.

Demerits: gymnosperms placed between dicots and monocots; Monochlamydeae is an artificial group (unrelated families such as Euphorbiaceae and Loranthaceae together); related families separated (e.g. Polypetalae and Gamopetalae families); Orchidaceae placed at the beginning of monocots though advanced; not phylogenetic.

Engler & Prantl's system – first major phylogenetic system, published in Die Natürlichen Pflanzenfamilien (23 volumes, 1887–1915) by Adolf Engler and Karl Prantl. Covers the whole plant kingdom.

Outline: Plant kingdom in 13 divisions; Division Embryophyta Siphonogama (seed plants) → subdivisions Gymnospermae and Angiospermae. Angiospermae → class Monocotyledoneae (placed first) and class Dicotyledoneae. Dicotyledoneae → subclass Archichlamydeae (petals absent or free) and Metachlamydeae / Sympetalae (petals fused). Starts with Amentiferae (catkin-bearing, unisexual, apetalous, e.g. Casuarinaceae).

Merits: covers the whole plant kingdom; gymnosperms correctly placed before angiosperms; Sympetalae treated as advanced; keys and illustrations for all genera; widely followed in Europe and America.

Demerits: monocots placed before dicots (now dicots are considered older); Amentiferae (simple, unisexual flowers) treated as primitive, though their simplicity is due to reduction; Ranales placed late; Helobiae placed before Liliiflorae; not truly phylogenetic in many places.

5 likely exam questions

Long answer

1. Give an outline of Bentham and Hooker's system of classification along with its merits and demerits.
2. What are modern trends in taxonomy? Discuss the role of cytotaxonomy and chemotaxonomy (proteins, flavonoids and betalains) in solving taxonomic problems.

Short answer / short notes

3. What is an OTU? Explain the steps of numerical taxonomy.
4. Distinguish between artificial, natural and phylogenetic systems of classification.
5. Write two merits and two demerits of Engler and Prantl's system.

Syllabus topics (official RTMNU)

1. Study of Families (Dicot): Malvaceae, Brassicaceae, Fabaceae (Papilionaceae, Caesalpiniaceae, Mimosaceae) and Solanaceae (Note: Taxonomic description along with economic importance are expected for all the families)

Study of Families (Dicot): Malvaceae, Brassicaceae, Fabaceae (Papilionaceae, Caesalpiniaceae, Mimosaceae) and Solanaceae

For each family learn: systematic position (Bentham & Hooker), vegetative characters, floral characters, floral formula, floral diagram and economic importance. Symbols: ⊕ actinomorphic, % zygomorphic, ⚥ bisexual, K calyx, C corolla, A androecium, G gynoecium, ( ) fused, + separate whorls, ∞ many.

Malvaceae (Mallow family)

Systematic position: Dicotyledons → Polypetalae → Thalamiflorae → Malvales → Malvaceae.

Distribution: about 80 genera, 1500 species; tropical and subtropical; common in India.

• Vegetative: herbs, shrubs or trees; young parts with stellate hairs and mucilage; leaves simple, alternate, stipulate, palmately veined.
• Flower: solitary axillary, large, bisexual, actinomorphic, pentamerous, hypogynous; epicalyx (whorl of bracteoles) usually present.
• Calyx: 5, gamosepalous, valvate. Corolla: 5, polypetalous, twisted, petals fused at base with staminal tube.
• Androecium: stamens many, monadelphous (staminal tube around style), epipetalous; anthers monothecous, reniform; pollen large, spiny.
• Gynoecium: 5 to many carpels, syncarpous, superior, axile placentation; style passes through staminal tube; stigmas as many as carpels.
• Fruit: capsule (cotton, bhindi) or schizocarp (Abutilon).

Floral formula: Epi_3–∞ ⊕ ⚥ K₍₅₎ C₅ A_(∞) G_(5–∞) – superior ovary, petals adnate to staminal tube.

Economic importance: Cotton – Gossypium hirsutum, G. arboreum (fibre, seed oil); Bhindi – Abelmoschus esculentus (vegetable); Ambadi – Hibiscus cannabinus (fibre, leaves eaten in Maharashtra); Gudhal – Hibiscus rosa-sinensis (ornamental); Althaea rosea (hollyhock, ornamental).

Brassicaceae (Cruciferae, Mustard family)

Systematic position: Dicotyledons → Polypetalae → Thalamiflorae → Parietales → Cruciferae.

Distribution: about 350 genera, 3000 species; mostly temperate.

• Vegetative: annual herbs with pungent watery juice (glucosinolates, mustard oil); leaves simple, alternate, exstipulate, often radical.
• Inflorescence: raceme (corymbose raceme), ebracteate.
• Flower: bisexual, actinomorphic, tetramerous, hypogynous.
• Calyx: 4 sepals in two whorls (2+2). Corolla: 4 free clawed petals arranged in a cross – cruciform.
• Androecium: 6 stamens, 2 short outer + 4 long inner – tetradynamous.
• Gynoecium: bicarpellary, syncarpous, superior, unilocular but becomes bilocular by a false septum (replum), parietal placentation.
• Fruit: siliqua (long) or silicula (short, e.g. Iberis).

Floral formula: ⊕ ⚥ K₂₊₂ C₄ A₂₊₄ G₍₂₎ – superior ovary.

Economic importance: Mustard – Brassica juncea (oil); Cabbage – B. oleracea var. capitata; Cauliflower – B. oleracea var. botrytis; Radish – Raphanus sativus; Turnip – B. rapa; Candytuft – Iberis amara (ornamental).

Fabaceae (Leguminosae, Pea family)

Systematic position: Dicotyledons → Polypetalae → Calyciflorae → Rosales → Leguminosae. Bentham & Hooker divided it into three subfamilies (now often raised to families).

Distribution: about 650 genera and 18,000 species; worldwide, third largest family of angiosperms.

Common characters: leaves compound, alternate, stipulate with pulvinus; roots with nitrogen-fixing nodules (Rhizobium); gynoecium monocarpellary, superior, unilocular, marginal placentation; fruit a legume (pod).

Economic importance: Pulses – gram Cicer arietinum, tur Cajanus cajan, moong Vigna radiata; oil – groundnut Arachis hypogaea, soybean Glycine max; timber – shisham Dalbergia sissoo; tamarind Tamarindus indica (fruit); Cassia fistula (amaltas, laxative); babul Acacia nilotica (gum, tannin); katha from Acacia catechu; Saraca asoca (sacred, medicinal).

Solanaceae (Potato / Nightshade family)

Systematic position: Dicotyledons → Gamopetalae → Bicarpellatae → Polemoniales → Solanaceae.

Distribution: about 90 genera, 2500 species; tropical America mainly.

• Vegetative: herbs or shrubs, sometimes prickly; bicollateral vascular bundles; leaves simple, alternate, exstipulate; often leaf displacement (leaves appear opposite in floral region).
• Inflorescence: extra-axillary cyme or solitary (Datura).
• Flower: bisexual, actinomorphic, pentamerous, hypogynous.
• Calyx: 5, gamosepalous, persistent (accrescent in Physalis). Corolla: 5, gamopetalous, rotate or infundibuliform, valvate or twisted.
• Androecium: 5, epipetalous, alternate with petals; anthers often open by apical pores (Solanum).
• Gynoecium: bicarpellary, syncarpous, superior, bilocular, ovary obliquely placed, swollen axile placenta with many ovules; falsely 4-locular in Datura.
• Fruit: berry (tomato, brinjal) or capsule (Datura, spiny).

Floral formula: ⊕ ⚥ K₍₅₎ C₍₅₎ A₅ G₍₂₎ – stamens epipetalous, superior ovary.

Economic importance: Potato – Solanum tuberosum; Tomato – S. lycopersicum; Brinjal – S. melongena; Chilli – Capsicum annuum; Tobacco – Nicotiana tabacum; Ashwagandha – Withania somnifera (medicine); Atropa belladonna (atropine); Datura (stramonium); Cestrum (raat-ki-rani, ornamental).

5 likely exam questions

Long answer

1. Describe the vegetative and floral characters of family Malvaceae. Give its floral formula, floral diagram and economic importance.
2. Compare the three subfamilies of Leguminosae (Papilionaceae, Caesalpiniaceae and Mimosaceae) and give the economic importance of the family.

Short answer / short notes

3. Give the systematic position and floral formula of Brassicaceae; explain tetradynamous stamens.
4. Write the floral characters of Solanaceae.
5. Name four economically important plants of Solanaceae with their scientific names and uses.

Syllabus topics (official RTMNU)

1. Study of Families (Dicot): Apocynaceae, Asteraceae, Asclepiadaceae, Euphorbiaceae
2. Study of Family (Monocot): Poaceae (Note: Taxonomic description along with economic importance are expected for all the families)

Study of Families (Dicot): Apocynaceae, Asteraceae, Asclepiadaceae, Euphorbiaceae

Apocynaceae (Periwinkle / Dogbane family)

Systematic position: Dicotyledons → Gamopetalae → Bicarpellatae → Gentianales → Apocynaceae. Distribution: about 200 genera, 2000 species; mainly tropical.

• Vegetative: herbs, shrubs, trees or twiners with milky latex; bicollateral bundles; leaves simple, opposite or whorled (Nerium – whorls of 3), exstipulate.
• Flower: cymose, bisexual, actinomorphic, pentamerous, hypogynous.
• Calyx: 5, gamosepalous. Corolla: 5, gamopetalous, salver- or funnel-shaped, twisted; corona present in Nerium.
• Androecium: 5, epipetalous; anthers sagittate, connivent around stigma but free from it (no pollinia).
• Gynoecium: bicarpellary, ovaries free (apocarpous) but styles united above; stigma large, dumb-bell shaped; marginal placentation.
• Fruit: pair of follicles (Catharanthus) or drupe (Thevetia, Carissa berry); seeds often hairy (comose).

Floral formula: ⊕ ⚥ K₍₅₎ C₍₅₎ A₅ G₂ – stamens epipetalous, superior ovary, carpels united only by style.

Economic importance: Sadabahar – Catharanthus roseus (vinblastine, vincristine – anticancer); Sarpagandha – Rauvolfia serpentina (reserpine for high blood pressure); Kaner – Nerium oleander and yellow oleander Thevetia peruviana (ornamental, poisonous); Karonda – Carissa carandas (fruit, hedge); Chafa/Frangipani – Plumeria rubra (ornamental).

Asteraceae (Compositae, Sunflower family)

Systematic position: Dicotyledons → Gamopetalae → Inferae → Asterales → Compositae. Distribution: largest dicot family, about 1000 genera, 23,000 species; cosmopolitan.

• Vegetative: mostly herbs; some with latex (Lactuca); leaves simple, alternate or opposite, exstipulate.
• Inflorescence: capitulum (head) surrounded by an involucre of bracts; florets on a flat receptacle, often with scales (paleae).
• Two kinds of florets: (a) ray florets – marginal, zygomorphic, ligulate (strap-shaped), pistillate or neuter; (b) disc florets – central, actinomorphic, tubular, bisexual. Heads may be heterogamous (both, e.g. sunflower) or homogamous (only disc – Vernonia, Ageratum; only ray – Sonchus, Lactuca).
• Calyx: modified into pappus (hairs/scales) or absent. Corolla: 5, gamopetalous.
• Androecium: 5, epipetalous, syngenesious (anthers fused, filaments free).
• Gynoecium: bicarpellary, syncarpous, inferior, unilocular, one basal ovule; style bifid.
• Fruit: cypsela with pappus for wind dispersal.

Floral formulae: Ray floret: % ♀ K_pappus C₍₅₎ A₀ G₍₂₎; Disc floret: ⊕ ⚥ K_pappus C₍₅₎ A₍₅₎ G₍₂₎ – inferior ovary, anthers syngenesious and epipetalous.

Economic importance: Sunflower – Helianthus annuus (oil); Safflower/Kardai – Carthamus tinctorius (oil, grown in Maharashtra); Lettuce – Lactuca sativa; Artemisia annua (artemisinin, antimalarial); Marigold – Tagetes erecta, Chrysanthemum, Dahlia, Zinnia (ornamental); Parthenium hysterophorus – harmful weed (allergy).

Asclepiadaceae (Milkweed family)

Systematic position: Dicotyledons → Gamopetalae → Bicarpellatae → Gentianales → Asclepiadaceae (now merged in Apocynaceae by APG). Distribution: about 250 genera, 2000 species; tropics.

• Vegetative: herbs, shrubs or twiners with milky latex; leaves simple, opposite, exstipulate.
• Flower: umbellate cymes, bisexual, actinomorphic, pentamerous, hypogynous.
• Calyx: 5, free or slightly united. Corolla: 5, gamopetalous, rotate, with a corona (outgrowths from stamens/corolla).
• Androecium: 5, filaments fused into a tube; anthers fused with the stigma to form a gynostegium. Pollen of each anther lobe forms a waxy mass – pollinium; two pollinia of adjacent anthers are joined by a translator (corpusculum + two retinacula).
• Gynoecium: bicarpellary, ovaries free, styles free but stigmas united into a large 5-angled stigmatic disc.
• Fruit: a pair of follicles; seeds comose (silky hairs).

Floral formula: ⊕ ⚥ K₅ C₍₅₎ A₍₅₎ G₂ – anthers united with stigma (gynostegium), superior ovary.

Economic importance: Rui/Aak – Calotropis procera and C. gigantea (latex medicinal, floss fibre); Anantmool – Hemidesmus indicus (medicinal root, blood purifier); Gudmar – Gymnema sylvestre (used in diabetes); Hoya (wax plant) and Cryptostegia grandiflora (ornamental, rubber); Leptadenia reticulata (jivanti, medicinal).

Euphorbiaceae (Spurge family)

Systematic position: Dicotyledons → Monochlamydeae → Unisexuales → Euphorbiaceae. Distribution: about 300 genera, 7500 species; tropics.

• Vegetative: herbs, shrubs, trees, often with latex; some xerophytic and cactus-like (Euphorbia); leaves simple or palmately compound (Ricinus lobed, Hevea trifoliate), stipulate.
• Inflorescence: raceme or panicle (Ricinus); special cyathium in Euphorbia – a cup-like involucre with nectar glands, containing one central female flower (stalked) and many male flowers each reduced to a single stamen, arranged in scorpioid cymes.
• Flowers: unisexual, monoecious or dioecious, actinomorphic; perianth 0–5 (monochlamydeous).
• Male: stamens one to many, free or branched (Ricinus). Female: tricarpellary, syncarpous, superior, trilocular, axile placentation, 1–2 ovules per locule with caruncle on seed.
• Fruit: schizocarpic capsule (regma) splitting into three cocci.

Floral formulae: Male: ⊕ ♂ P_0–5 A_1–∞ G₀; Female: ⊕ ♀ P_0–5 A₀ G₍₃₎ – superior ovary.

Economic importance: Rubber – Hevea brasiliensis; Tapioca – Manihot esculenta; Castor – Ricinus communis (oil, lubricant, purgative); Amla – Phyllanthus emblica (vitamin C); Jatropha – Jatropha curcas (biodiesel); Poinsettia – Euphorbia pulcherrima, Croton (Codiaeum) (ornamental).

Study of Family (Monocot): Poaceae

Poaceae (Gramineae, Grass family) – Systematic position: Monocotyledons → Glumaceae → Gramineae. Distribution: about 700 genera, 10,000 species; cosmopolitan, ecologically dominant.

• Vegetative: herbs (bamboo woody); fibrous roots, stilt roots in maize; stem a culm with solid nodes and hollow internodes; leaves alternate, distichous, with sheath, ligule and long linear blade, parallel venation.
• Inflorescence: unit is a spikelet; spikelets arranged in spikes or panicles. Each spikelet has two sterile glumes at the base and one or more florets.
• Floret: enclosed by lemma (lower, often awned) and palea (upper); bisexual, zygomorphic.
• Perianth: represented by 2 (rarely 3) small scales called lodicules, which swell to open the floret.
• Androecium: usually 3 stamens (6 in rice, bamboo); anthers versatile, filaments long – adaptations for wind pollination.
• Gynoecium: monocarpellary (tricarpellary reduced), superior, unilocular, one ovule; 2 feathery stigmas.
• Fruit: caryopsis (pericarp fused with seed coat); endospermic seed.

Floral formula: % ⚥ P₂ (lodicules) A₃ G₁ – superior ovary.

Economic importance: Cereals – wheat Triticum aestivum, rice Oryza sativa, maize Zea mays, jowar Sorghum bicolor, bajra Pennisetum glaucum; sugarcane – Saccharum officinarum; bamboo – Bambusa, Dendrocalamus strictus (paper, construction); lemongrass – Cymbopogon citratus (oil); doob grass – Cynodon dactylon (fodder, lawns).

5 likely exam questions

Long answer

1. Describe the characteristic features of family Asteraceae with special reference to its inflorescence and florets. Add a note on its economic importance.
2. Give the systematic position, floral characters and economic importance of Euphorbiaceae. Describe the cyathium inflorescence with a labelled diagram.

Short answer / short notes

3. What are pollinia and translator? Name the family in which they are found.
4. Give the floral formula of Poaceae and explain the structure of a spikelet.
5. Write any four economically important plants of Apocynaceae with their uses.