Unit 5: Angiosperm Families
This unit covers the key characters of important angiosperm families. Below is a summary for each.
Magnoliaceae (The Magnolia Family)
- Distinguishing Characters: Primitive family. Large, solitary flowers with numerous parts arranged spirally on an elongated thalamus. Stipules are large and enclose the bud, leaving a circular stipular scar.
- Vegetative: Trees or shrubs; leaves simple, alternate.
- Floral: Flower large, actinomorphic, ⚥. Perianth (tepals) of 6 to many, free. Androecium: Stamens numerous, free, spirally arranged. Gynoecium: Carpels numerous, free (apocarpous), spirally arranged on the thalamus. Ovary superior.
- Fruit: An aggregate of follicles or samaras (e.g., Liriodendron).
- Economically Important Plants: Magnolia grandiflora (Ornamental), Michelia champaca (Champa, for perfume/ornamental).
Asteraceae (The Sunflower Family)
- Distinguishing Characters: Inflorescence is a capitulum (head) surrounded by an involucre of bracts. Calyx is modified into a pappus (hairs or scales) for fruit dispersal. Stamens are syngenesious (anthers fused into a tube, filaments free). Ovary inferior, basal placentation.
- Floral: Flowers (florets) are small, sessile, and arranged on a flat receptacle. They can be:
- Ray Florets: Zygomorphic, ligulate (strap-shaped), often sterile or female.
- Disc Florets: Actinomorphic, tubular, bisexual.
- Fruit: A cypsela (an achene from an inferior ovary).
- Economically Important Plants: Helianthus annuus (Sunflower), Tagetes patula (Marigold), Lactuca sativa (Lettuce).
Solanaceae (The Potato/Nightshade Family)
- Distinguishing Characters: Leaves alternate. Flower actinomorphic, ⚥. Calyx K(5), persistent (remains attached to fruit). Corolla C(5), gamopetalous (fused petals). Stamens A5, epipetalous (attached to petals). Gynoecium G(2) (bicarpellary, syncarpous), ovary superior, swollen placenta with axile placentation, ovary obliquely placed.
- Fruit: A berry (e.g., Tomato, Brinjal) or a capsule (e.g., Datura).
- Floral Formula: ⊕ ⚥ K(5) C(5) A5 G(2) (Superior)
- Economically Important Plants: Solanum tuberosum (Potato), Solanum lycopersicum (Tomato), Solanum melongena (Brinjal), Capsicum annuum (Chilli), Nicotiana tabacum (Tobacco), Atropa belladonna (medicinal).
Lamiaceae (The Mint/Tulsi Family)
- Distinguishing Characters: Stem is typically quadrangular (square). Leaves are simple, opposite, and strongly aromatic. Inflorescence is a verticillaster. Flower zygomorphic, ⚥. Corolla C(5), bilabiate (two-lipped). Gynoecium G(2), ovary superior, with a false septum making it four-lobed. A gynobasic style arises from the base of the four ovary lobes.
- Fruit: A schizocarp of 4 nutlets.
- Economically Important Plants: Ocimum sanctum (Tulsi), Mentha (Mint), Salvia (Sage), Lavandula (Lavender).
Euphorbiaceae (The Spurge Family)
- Distinguishing Characters: A highly diverse family, often with milky latex. Flowers are unisexual (plants monoecious or dioecious). Inflorescence is often a cyathium (in Euphorbia). Gynoecium G(3) (tricarpellary, syncarpous), ovary superior, axile placentation, with 1-2 ovules per locule.
- Fruit: A schizocarpic capsule (regma) that splits into three one-seeded parts.
- Economically Important Plants: Hevea brasiliensis (Rubber tree), Manihot esculenta (Cassava/Tapioca), Ricinus communis (Castor oil), Euphorbia pulcherrima (Poinsettia).
Moraceae (The Fig/Mulberry Family)
- Distinguishing Characters: Trees or shrubs, usually with milky latex. Leaves alternate, with prominent stipules that leave a circular scar. Flowers small, unisexual, densely clustered. Inflorescence is specialized, often a hypanthodium (fig) or catkin (mulberry).
- Fruit: A multiple fruit (syconus in fig, sorosis in mulberry).
- Economically Important Plants: Ficus carica (Fig), Ficus religiosa (Peepal), Morus alba (Mulberry, for silkworms), Artocarpus heterophyllus (Jackfruit).
Orchidaceae (The Orchid Family)
- Distinguishing Characters: Terrestrial or epiphytic herbs (with velamen roots to absorb moisture). Flowers are highly specialized, zygomorphic. Perianth of 6 tepals, the inner median one is modified into a large, prominent labellum (lip). Stamens (1 or 2) and pistil are fused into a central structure called the column (gynostemium). Pollen grains are aggregated into masses called pollinia. Ovary inferior.
- Fruit: A capsule, containing innumerable, minute, non-endospermic seeds.
- Economically Important Plants: Vanilla planifolia (Vanilla), Phalaenopsis, Cattleya (Ornamentals).
Liliaceae (The Lily Family)
- Distinguishing Characters: Monocot herbs, often with underground bulbs or rhizomes. Flower actinomorphic, ⚥. Perianth P(3+3) (6 tepals in two whorls, often large and colorful, free or fused). Stamens A(3+3), free or epiphyllous (attached to tepals). Gynoecium G(3) (tricarpellary, syncarpous), ovary superior, axile placentation.
- Fruit: A capsule or berry.
- Economically Important Plants: Allium cepa (Onion), Allium sativum (Garlic), Aloe vera, Lilium (Lily, ornamental).
Musaceae (The Banana Family)
- Distinguishing Characters: Large monocot herbs with a pseudostem (formed by tightly overlapping leaf sheaths). Leaves are very large, spirally arranged, with a thick midrib and parallel venation. Inflorescence is a large terminal spadix, with colorful, boat-shaped bracts (spathes). Flowers unisexual. Ovary inferior.
- Fruit: A fleshy berry (e.g., Banana).
- Economically Important Plants: Musa paradisiaca (Banana/Plantain).
Poaceae / Gramineae (The Grass Family)
- Distinguishing Characters: Monocot, stem is a post>culm (round, hollow internodes, solid nodes). Leaves have a sheathing leaf base and a small appendage called a ligule. Inflorescence is a compound spike, raceme, or panicle, made of basic units called spikelets. Each spikelet is subtended by two bracts called glumes. Each flower (floret) is enclosed by two bracts: lemma (outer) and palea (inner).
- Floral: Perianth reduced to 2-3 minute scales (lodicules). Stamens 3, with versatile anthers. Gynoecium G(1), ovary superior, with feathery stigmas.
- Fruit: A caryopsis (grain), where the seed coat is fused to the fruit wall.
- Economically Important Plants: Oryza sativa (Rice), Triticum aestivum (Wheat), Zea mays (Maize), Saccharum officinarum (Sugarcane), Bambusa (Bamboo).
Flower Morphology of Orchids
Orchids have one of the most highly evolved and specialized flowers in the plant kingdom, adapted for specific pollinators.
- Zygomorphy: The flower is strongly bilateral (zygomorphic).
- Labellum (Lip): One of the three petals (the median, inner one) is highly modified in size, shape, and color to act as a landing platform for pollinators.
- Column (Gynostemium): The stamens and the pistil (style and stigma) are completely fused together to form a single, complex structure in the center of the flower. This ensures precise pollen transfer.
- Pollinia: The pollen grains are not loose and powdery. They are aggregated into 1, 2, 4, or 8 waxy masses called pollinia. The entire pollinium (with its stalk) is typically removed by the pollinator as a single unit.
- Ovary: The ovary is inferior and contains thousands to millions of tiny ovules.