Samacheer Class 11 Bio Botany - Reproductive Morphology

Placentation refers to the arrangement of placentae (the tissue to which ovules are attached) within the ovary. Understanding different types of placentation is crucial for plant classification and identification. Marginal placentation occurs when the placentae are located along the margin of a unicarpellate ovary, as seen in members of Fabaceae. Axile placentation is found in compound ovaries with septa, where the placentae arise from the central column or axis, characteristic of Hibiscus, tomato, and lemon. Superficial placentation displays ovules arising from the surface of the septa within the ovary, exemplified by Nymphaeaceae. Parietal placentation occurs when the placentae are located on the ovary walls or upon intruding partitions of a unilocular compound ovary, as in Mustard, Argemone, and Cucumber. Free-central placentation is characterized by placentae along the central column in a compound ovary without septa, typical of Caryophyllaceae, Dianthus, and Primrose. Basal placentation shows the placenta located at the base of the ovary, as seen in Sunflower (Asteraceae) and Marigold. Each type of placentation represents a different pattern of ovule distribution within the ovary and is an important diagnostic feature for plant families and genera.

The anther attachment to the filament varies based on the point of connection and the nature of the filament. Basifixed attachment occurs when the base of the anther is attached to the tip of the filament, as seen in Datura. Dorsifixed attachment is when the apex of the filament is attached to the dorsal side of the anther, characteristic of Hibiscus and many other plants. Versatile attachment describes the condition where the filament is attached to the anther at the midpoint, allowing the anther to swing freely, which is typical in grasses and many wind-pollinated flowers. Adnate attachment occurs when the filament is continuous from the base to the apex of the anther, meaning the filament runs along the entire length of the anther, as observed in Ranunculus. These different types of anther attachment have functional significance in pollen dispersal and pollination mechanisms.

The correct answers for the parts of the fruits mentioned are as follows: Apple is a pome fruit, where the edible fleshy part is primarily the thalamus, which becomes fleshy and encloses the true fruit. Coconut is a drupe, and its edible part is the oily endosperm. Jackfruit is a multiple fruit, and its edible parts are the fleshy perianth and the seeds. Mango is also a drupe, and its edible part is the fleshy and juicy mesocarp. Tomato is a berry, and its edible part consists of the epicarp, mesocarp, and endocarp, collectively known as the pericarp. Orange is a hesperidium, a type of berry, and its edible part consists of juicy hairs (placental hairs) within the locules. Pomegranate is a balausta, and its edible part is the juicy testa of the seeds.

Pomology is the study of fruits and their characteristics, including their development, classification, and uses. Ikebana is the Japanese art of flower arrangement that emphasizes aesthetic principles and the harmonious placement of flowers and plant materials. The botanical name of saffron flower is Crocus sativus, a plant valued for its stigmas which are used as a spice. Kurinji, scientifically known as Strobilanthus kunthianus, is a flowering plant that blooms once every twelve years in the Western Ghats of India, creating a spectacular blue carpet on the hillsides. Lodoicea maldivica, also called the double coconut or coco de mer, produces the world's largest fruit, which can weigh up to 20 kilograms. A viable seed from King Herod's palace near the Dead Sea was successfully germinated after remaining dormant for approximately 2,000 years, demonstrating the remarkable longevity of some seeds. Corypha umbraculifera, commonly known as the talipot or cudai palm, produces the longest and largest inflorescence of any flowering plant, with a massive branched flower cluster. Rafflesia arnoldi is recognized as the largest single flower in the world, with flowers that can reach up to one meter in diameter.

Racemose and cymose inflorescences differ in several fundamental characteristics related to their growth pattern and flower arrangement. In racemose inflorescence, the main axis shows unlimited growth, meaning it continues to grow and produce new flowers throughout the flowering season, whereas in cymose inflorescence, the main axis has limited growth and terminates in a flower. The arrangement of flowers differs in that racemose inflorescence exhibits acropetal succession, where flowers open from the base toward the apex, while cymose inflorescence shows basipetal succession, where flowers open from the apex toward the base. The opening pattern of flowers is centripetal in racemose inflorescence, meaning flowers open from the periphery toward the center, whereas in cymose inflorescence it is centrifugal, with flowers opening from the center toward the periphery. The position of the oldest flower also differs: in racemose inflorescence, the oldest flower is located at the base of the main axis, while in cymose inflorescence, the oldest flower is at the top or apex of the main axis.

Monoecious, dioecious, and polygamous plants differ in the distribution and types of flowers they produce. Monoecious plants, meaning one house, have both male and female flowers present on the same individual plant, though the flowers are separate and unisexual. Examples of monoecious plants include coconut, maize, and cucumber, where male flowers produce pollen and female flowers produce seeds on the same plant. Dioecious plants, meaning two houses, have male and female flowers on completely separate plants, so one plant produces only male flowers while another plant produces only female flowers. Examples include papaya, ginkgo, and date palm, where individual plants are either entirely male or entirely female. Polygamous plants have male flowers, female flowers, and bisexual flowers all occurring on the same individual plant, providing a combination of both unisexual and bisexual flowers. Mangifera (mango) is a classic example of a polygamous plant, where staminate flowers, pistillate flowers, and perfect bisexual flowers can all be found on the same tree.

Bracts and bracteoles are both modified leaf-like structures associated with flowers, but they differ in their position and origin. A bract is a reduced, scale-like or leaf-like structure found at the base of the pedicel of a flower, or at the base of an inflorescence. It is typically subtending a flower or a cluster of flowers. The presence of a bract indicates that the flower or inflorescence is 'bracteate,' while its absence means it is 'ebracteate.' On the other hand, a bracteole is a smaller, often paired, scale-like or leaf-like structure that arises on the pedicel itself, usually above the bract but below the flower. Bracteoles are generally found closer to the flower than bracts. The presence of bracteoles makes a flower 'bracteolate,' and their absence makes it 'ebracteolate.' Essentially, bracts are associated with the main axis or peduncle, while bracteoles are found on the secondary axis or pedicel.

Fruits hold significant importance in both the plant's life cycle and for various other organisms, including humans. Firstly, the edible part of many fruits serves as a crucial source of food and energy for a wide range of animals, facilitating their survival and indirectly aiding in seed dispersal. Secondly, fruits are rich in numerous beneficial chemicals, such as sugars, pectin, various organic acids, essential vitamins, and vital minerals, making them highly nutritious. Thirdly, a primary biological function of the fruit is to protect the developing seeds from adverse climatic conditions, such as extreme temperatures or desiccation, and from predation by animals. Fourthly, both fleshy and dry fruits play a pivotal role in the dispersal of seeds, enabling plants to colonize new areas and reduce competition with parent plants. This dispersal can occur through various mechanisms, including consumption by animals (endozoochory) or physical means like wind or water. In certain specific instances, the fruit itself may provide initial nutrition to the germinating seedling, offering a crucial energy reserve for its early growth. Lastly, many fruits and their components have been utilized by humans as sources of traditional and modern medicine due to their diverse biochemical properties.

The posterior and anterior sides of a flower are determined by their orientation relative to the mother axis or main stem of the plant. The posterior side of a flower is the side that faces toward the mother axis or the main stem of the plant, also referred to as the adaxial side or the side toward the plant. This side is typically closer to the central axis from which the flower arises. The anterior side of a flower is the side that faces away from the mother axis, directed outward from the plant, also called the abaxial side or the side away from the plant. This distinction is important in floral morphology and taxonomy because certain floral parts show consistent orientation relative to these sides. For example, in zygomorphic flowers, the plane of symmetry often runs through the posterior and anterior sides, and specific petals or stamens may be positioned characteristically on one side or the other, which helps in plant identification and classification.

A superior ovary is one in which the sepals, petals, and stamens are attached at the base of the ovary, below it. The ovary occupies the highest position in the flower, and other floral parts are arranged below it. Examples include Hibiscus and Mangifera. In contrast, an inferior ovary is one in which the sepals, petals, and stamens are attached at the apex or top of the ovary, appearing to arise above it. The ovary is positioned below the other floral parts and becomes fused with the receptacle. Examples include Ixora and Musa. The key distinction lies in the relative position of the ovary with respect to the attachment points of other floral whorls. This difference is important in flower classification and is used to distinguish between hypogynous flowers (superior ovary) and epigynous flowers (inferior ovary).

Aestivation: Arrangement of sepals and petals in the flowers bud.
* Types: There are 5 types
* Valvate: Margins of sepals and petals do not overlap but touch each other.
Eg. Calyx — malvaceac inem bers.
* Twisted or convolute or contorted: One margin of each petal or sepal overlapping on
the other petal – Eg. Corolla of Malvaceae (china i-ose)
* Imbricate: Sepals\ Petalsepals petaals – overlap irregularly one member of the whorl-
exterior another interior other three one margin exterior other interior
3 types
* Ascending-imbricate Eg. Cassia,
*. Descendingly-imbricate (vexillary aestivation) Eg. Clihoria,
*. Quincuncial- Eg. Guava

Cyathium and coenanthium are two distinct specialized inflorescence types found in different plant families. A cyathium is a highly specialized inflorescence found in Euphorbia and related genera. It consists of a single female flower surrounded by many male flowers, all enclosed within a common involucre made of bracts. The flowers within the cyathium are naked or aclamydeous, meaning they lack both sepals and petals. An important feature of the cyathium is the presence of extrafloral nectaries in the involucre, which serve to attract pollinators. The entire structure resembles a single flower but is actually a condensed inflorescence. In contrast, a coenanthium is a circular, disc-like, fleshy open receptacle that bears many flowers. The pistillate or female flowers are typically located at the center of the receptacle, while the staminate or male flowers are arranged at the periphery. Unlike the cyathium, the coenanthium lacks an involucre and has an open receptacle. Dorsenia is a characteristic example of a coenanthium. The key differences are that cyathium has an involucre with a single female flower and extrafloral nectaries, while coenanthium is an open fleshy receptacle with multiple female flowers at the center and male flowers at the periphery.

Placentation refers to the arrangement of ovules within the ovary of a flower. This arrangement is a significant taxonomic character used in plant classification. There are several distinct types of placentation: Marginal placentation is characteristic of a unicarpellate (single carpel) ovary, where the placentae bearing the ovules develop along the fused margins of the carpel, forming a single ridge. An excellent example is found in members of the Fabaceae family, such as peas. Axile placentation occurs in a compound ovary that is multilocular (divided into multiple chambers by septa). The placentae arise from the central column where the septa meet, with ovules attached to this central axis in each locule. Examples include Hibiscus, tomato, and lemon. Superficial placentation is observed in multilocular ovaries where the ovules develop over the entire inner surface of the septa, rather than being restricted to a central column or margins. This type is relatively rare, seen in plants like Nymphaeaceae (water lilies). Parietal placentation is found in a unilocular (single-chambered), compound ovary where the placentae develop on the inner walls of the ovary, or on intruding partitions that do not meet in the center. Examples include mustard, Argemone, and cucumber. Free-central placentation occurs in a compound ovary that is unilocular (lacks septa), where the placentae arise from a central column that is not attached to the ovary walls. Examples are found in the Caryophyllaceae family, such as Dianthus, and Primrose. Basal placentation is characterized by a single ovule attached directly to the base of the ovary. This is a common type in unilocular ovaries. Examples include members of the Asteraceae family, such as sunflower and marigold.

Homogamous and heterogamous heads are two types of inflorescence found in the Asteraceae family, differing in the types of florets they contain. A homogamous head contains only one kind of floret throughout the inflorescence. There are two subtypes: heads with only tongue florets or ray florets, such as in Launaea, where all florets are ligulate with a flattened, strap-like corolla; and heads with only tube florets or disc florets, such as in Vernonia, where all florets have a tubular corolla. In contrast, a heterogamous head contains two different types of florets. The tongue florets or ray florets are located towards the periphery of the head and have a flattened, strap-like appearance. The tube florets or disc florets are located at the center and have a tubular corolla. This arrangement creates a visually distinctive inflorescence with different colored or shaped florets in different regions. Examples of heterogamous heads include Helianthus (sunflower) and Tridax, where the yellow ray florets at the periphery surround the yellow or orange disc florets at the center. The distinction between homogamous and heterogamous heads is important for plant identification and classification within the Asteraceae family.

The floral diagram and description for Cocos nucifera (coconut) differentiate between its male and female flowers, as it is a monoecious plant. The male flower is unisexual and actinomorphic, meaning it can be divided into two equal halves in any radial plane. It is bracteate and bracteolate, indicating the presence of bracts and bracteoles. It is an incomplete flower, lacking some floral whorls. The perianth consists of six tepals arranged in two whorls of three each, with an outer valvate aestivation and an inner imbricate aestivation, and they are apophyllous (free). The androecium comprises six stamens, also in two whorls of three, which are free, and the anthers are dithecous (having two pollen sacs). The gynoecium is absent, but a rudimentary pistillode may be present. The floral formula for the male flower can be represented as ♂ Br Brl ⊕ P(3+3) A(3+3) G0. The female flower is also unisexual and actinomorphic. It is bracteolate but ebracteolate, meaning it lacks bracts but has bracteoles. It is also an incomplete flower. The perianth consists of six tepals in two whorls of three, with the outer whorl showing valvate aestivation and the inner whorl imbricate aestivation, and they are apophyllous. The androecium is absent, though staminodes (sterile stamens) may be present. The gynoecium is tricarpellary (composed of three carpels), trilocular (three-chambered), and syncarpous (fused carpels), with a superior ovary. The ovules exhibit axile placentation. The floral formula for the female flower can be represented as ♀ Brl ⊕ P(3+3) A0 G(3) superior, with axile placentation indicated by the G(3) and the superior ovary symbol. These diagrams and formulas effectively summarize the structural characteristics of the flowers.

The ovary can be classified into three distinct types based on its position relative to other floral parts. The superior ovary is found in hypogynous flowers where the sepals, petals, and stamens are attached at the base of the ovary. The ovary occupies the highest position in the flower, and all other floral whorls are positioned below it. This arrangement is common in many plant families. The inferior ovary is found in epigynous flowers where the sepals, petals, and stamens are attached at the apex or top of the ovary. The ovary is positioned below the other floral parts and is typically fused with the receptacle, making it appear sunken. This type is found in plants like orchids and members of Asteraceae. The half-inferior ovary, also called semi-inferior ovary, is found in perigynous flowers where the sepals, petals, stamens, or the hypanthium are attached near the middle of the ovary. In this case, the ovary is partially embedded in the receptacle, appearing neither completely superior nor completely inferior. This type is found in plants like roses and members of Rosaceae. These three types represent different degrees of fusion between the ovary and the receptacle, which is an important characteristic in flower morphology and plant classification.

Apocarpous and syncarpous conditions refer to the arrangement and fusion of carpels within the gynoecium. An apocarpous pistil contains two or more distinct carpels that remain separate and unfused from each other. Each carpel functions independently, with its own style and stigma. The carpels may be arranged in a whorl around the receptacle. Examples of apocarpous flowers include Annona, where multiple carpels are distinctly visible and separate. Apocarpous condition is considered more primitive from an evolutionary perspective. In contrast, a syncarpous pistil contains two or more carpels that are fused or united together to form a single compound ovary. The carpels lose their individual identity and function as a single unit. The fused carpels share a common ovary chamber or may have separate locules depending on the degree of fusion. Examples of syncarpous flowers include Citrus and tomato, where the carpels are completely fused into a single ovary. Syncarpous condition is considered more advanced evolutionarily. The key distinction is that apocarpous carpels remain distinct and separate, while syncarpous carpels are fused together into a unified structure. This difference affects the structure of the ovary, the number of locules, and the overall flower morphology.

Anthophore, androphore, gynophore, and gynandrophore are specialized elongations of the floral axis that occur between different floral whorls. An anthophore is an internodal elongation that occurs between the calyx and the corolla. It extends the distance between these two whorls, elevating the corolla above the calyx. Silene conoidea is a characteristic example where this structure is prominent. An androphore is an internodal elongation that occurs between the corolla and the androecium. It elevates the stamens above the corolla, creating a distinct separation between these whorls. Grewia is an example where the androphore is present. A gynophore is an internodal elongation that occurs between the androecium and the gynoecium. It elevates the pistil or carpels above the stamens, creating a stalk-like structure supporting the ovary. Capparis is a characteristic example of a plant with a prominent gynophore. A gynandrophore is a unified internodal elongation that occurs between the corolla and the androecium as well as between the androecium and the gynoecium. It represents a combined elongation affecting multiple floral whorls, elevating both the stamens and pistil together above the corolla. Gynandropsis is a classic example where this structure is well-developed. These elongations are important adaptations that affect pollinator access and flower morphology.

A carpel is a modified leaf-like structure that forms the basic unit of the gynoecium or female reproductive organ of a flower. Carpels are the components of the gynoecium and may be distinct and separate from each other or fused together. The number of carpels in a flower is often constant within a species and is used as a diagnostic character in plant classification. Each carpel typically consists of an ovary at the base, a style in the middle, and a stigma at the apex. A locule is a cavity or chamber within the ovary formed by the walls of the ovary and the cross-walls or septa that divide the ovary internally. The locule is the space where ovules develop and are attached to the placenta. In most cases, the number of locules equals the number of carpels, as each carpel typically forms one locule. However, there are exceptions to this general rule. For example, in the Asteraceae family, there is a bicarpellary unilocular condition where two carpels are present but only one locule is formed due to the suppression or abortion of the septa. Understanding the relationship between carpels and locules is essential for flower morphology and plant identification, as these features are used to classify and distinguish between different plant families and genera.

Dry indehiscent fruits are fruits that do not open or split to release their seeds at maturity. They have a hard, protective pericarp that remains intact. Achene is a monocarpellary superior ovary fruit from an apocarpous flower where the pericarp is free from the seed coat, found in Clematis and strawberry. Cypsela is a bicarpellary inferior ovary syncarpous fruit with reduced scales and hairy or feathery calyx lobes forming a pappus, found in Tridax and Helianthus. Caryopsis is a monocarpellary superior ovary fruit where the fruit wall is inseparably fused with the seed coat, found in Oryza and Triticum. Nut is a multicarpellary syncarpous superior ovary fruit with a hard, woody, or bony pericarp, found in Anacardium. Samara is a monocarpellary superior ovary fruit where the pericarp develops into a thin, wing-like structure that aids in wind dispersal, found in Pterocarpus. Utricle is a bicarpellary unilocular syncarpous superior ovary fruit where the pericarp loosely encloses the seed without being fused to it, found in Chenopodium. Each fruit type has specific characteristics related to the nature of the ovary and the development of the pericarp, which are important for plant identification and understanding seed dispersal mechanisms.

This fruit type of intermediate between dehiscent and indehiscent fruit. The fruit instead of dehiscing rather splits into a number of segments, each containing one or more seeds. They are of the following types:
* Cremocarp: Fruit develops from bicarpellary, syncarpous, inferior ovary and splitting into two one-seeded segments known as mericarps. e.g., Coriander and Carrot.
* Carcerulus: Fruit develops from bicarpellary, syncarpous, superior ovary and splitting into four one-seeded segments known as nutlets, e.g., Leucas, Ocimum and Abutilon.
* Lomentum: The fruit is derived from monocarpellary, unilocular ovary. A leguminous fruit, constricted between the seeds to form a number of one seeded compartments that separate at maturity, e.g., Desmodium, Arachis and Mimosa.
* Regma: They develop from tricarpellary, syncarpous, superior, trilocular ovary and splits into one-seeded cocci which remain attached to carpophore, e.g., Ricinus and Geranium.

Achene and caryopsis are both indehiscent, one-seeded fruits that develop from a monocarpellary ovary, meaning they do not open naturally at maturity and contain a single seed. However, they differ significantly in the relationship between the pericarp and seed coat. In an achene, the pericarp remains hard and leathery and stays free from the seed coat, remaining as a distinct layer around the seed. Examples of achenes include fruits from Clematis and buttercups. In contrast, a caryopsis has a pericarp that is completely fused with the seed coat, so these two layers cannot be separated. This fusion is a defining characteristic of caryopsis fruits. The caryopsis is the typical fruit type found in grasses and cereals, with paddy or rice being a common example. Despite their similarities in being single-seeded indehiscent fruits from monocarpellary ovaries, the fusion or separation of the pericarp and seed coat is the key distinguishing feature between these two fruit types.

Anthers are classified into various types based on how their filament attaches to the anther lobes. This mode of attachment is an important morphological feature. The main types include: Firstly, Basifixed, also known as Innate, where the base of the anther is rigidly attached to the very tip of the filament. This creates a stable connection, and examples of plants exhibiting this type are Brassica (mustard) and Datura. Secondly, Dorsifixed, in which the apex of the filament is attached to the dorsal (back) side of the anther, usually somewhere along its length but not at the base. This allows for some movement of the anther. Citrus and Hibiscus are common examples of plants with dorsifixed anthers. Thirdly, Versatile, a specialized type of dorsifixed attachment where the filament is attached to the anther at its midpoint, allowing the anther to swing freely, often facilitating pollen dispersal by wind. This type is characteristic of grasses (Poaceae). Lastly, Adnate, where the filament extends along the entire length of the anther, from its base to its apex, creating a broad and often fused attachment. Examples of plants with adnate anthers include Verbena, Ranunculus, and Nelumbo (lotus). These different attachment types influence the presentation of pollen and can be adaptations for various pollination mechanisms.

Dicotyledonous and monocotyledonous seeds differ in several fundamental structural and functional characteristics. Dicotyledonous seeds contain two cotyledons, which are seed leaves that typically store large amounts of food material, becoming thick and fleshy. These cotyledons nourish the seedling during its early development, and the endosperm is usually absent or consumed during seed maturation. Common examples of dicots include pea and bean seeds. Monocotyledonous seeds, in contrast, possess only a single cotyledon. In monocots, the endosperm persists as a distinct tissue within the mature seed and serves as the primary source of nutrition for the developing seedling during germination and early growth. The cotyledon in monocots is typically thin and functions mainly to absorb nutrients from the endosperm rather than storing them. Paddy or rice is a characteristic example of a monocot seed. The presence or absence of persistent endosperm and the number of cotyledons are therefore the major distinguishing features between these two seed types, reflecting their different strategies for nourishing the developing plant.

Albuminous and non-albuminous seeds are classified based on the presence or absence of endosperm in the mature seed. Albuminous seeds contain a persistent endosperm at maturity, which means the endosperm tissue remains intact and functional in the mature seed. In these seeds, the cotyledons are typically thin and membranous rather than thick and fleshy, as they do not serve as the primary storage organs. The persistent endosperm provides nutrition to the seedling during its early development and germination. Common examples of albuminous seeds include castor and sunflower. Non-albuminous seeds, conversely, lack endosperm at maturity because the food stored in the endosperm has been completely absorbed and transferred to the cotyledons during seed development. In these seeds, the cotyledons become thick, fleshy, and nutrient-rich, serving as the sole source of food for the developing seedling. The mature seed appears solid without any visible endosperm tissue. Pea and groundnut are typical examples of non-albuminous seeds. The key distinction lies in whether the mature seed retains endosperm for nutrition or relies entirely on food stored within the cotyledons.