Flowers are not merely morphological marvels but the sites of sexual reproduction. The reproductive process begins with Pre-fertilization: Structures and Events, initiated by hormonal and structural changes leading to the differentiation of the floral primordium. The male reproductive organ, the Androecium, consists of stamens. Each stamen has a filament and a terminal bilobed Anther. A typical angiosperm anther is dithecous (two-lobed) and tetrasporangiate, containing four microsporangia located at the corners. The microsporangium is surrounded by four wall layers: the epidermis, endothecium, middle layers, and the innermost tapetum. The outer three layers perform protection and help in dehiscence, while the tapetum nourishes the developing pollen grains; its cells possess dense cytoplasm and are often multinucleate. Through Microsporogenesis, the sporogenous tissue cells (Microspore Mother Cells or PMC) undergo meiosis to form microspore tetrads. As the anther matures and dehydrates, microspores dissociate to form Pollen Grains (male gametophytes). The pollen grain has a two-layered wall: the hard outer Exine made of sporopollenin (one of the most resistant organic materials known, withstands high temp/acids/alkali, no enzyme degrades it) which has apertures called germ pores, and the inner Intine made of cellulose and pectin. A mature pollen grain contains a large Vegetative cell (food reserve) and a small Generative cell (floats in vegetative cytoplasm). In 60% of angiosperms, pollen is shed at the 2-celled stage; in others, the generative cell divides to form two male gametes (3-celled stage).

The female reproductive part, the Gynoecium, may be monocarpellary or multicarpellary (syncarpous or apocarpous). The Pistil consists of the stigma, style, and ovary. inside the ovary is the ovarian cavity (locule) containing the placenta, from which arises the Megasporangium (Ovule). The ovule is attached to the placenta by a funicle; the junction is the hilum. Integuments enclose the nucellus (mass of cells with food reserve), leaving a small opening called the micropyle opposite the chalaza (basal part). Megasporogenesis involves the meiotic division of the Megaspore Mother Cell (MMC) to form four megaspores. In most flowering plants, one megaspore remains functional (chalazal end) while the other three degenerate (Monosporic development). The functional megaspore nucleus divides mitotically to form the Embryo Sac (female gametophyte). A typical mature angiosperm embryo sac is 8-nucleate but 7-celled. It contains an Egg Apparatus at the micropylar end (two synergids + one egg cell), three Antipodals at the chalazal end, and a large Central Cell with two polar nuclei. The synergids have a Filiform Apparatus to guide the pollen tube.

Pollination is the transfer of pollen to the stigma. It can be Autogamy (same flower, e.g., Viola, Oxalis, Commelina produce cleistogamous flowers that never open), Geitonogamy (different flower, same plant), or Xenogamy (different plant, genetically different pollen). Agents include abiotic (Wind/Anemophily – non-sticky pollen, feathery stigma; Water/Hydrophily – Vallisneria, Hydrilla, Zostera) and biotic (Animals/Zoophily). The Yucca moth and Yucca plant show an obligate relationship where the moth deposits eggs in the ovary locule while pollinating. Outbreeding devices (like self-incompatibility or non-synchronized receptivity) encourage cross-pollination. Pollen-pistil interaction determines compatibility.

Double Fertilization is a unique event in angiosperms. The pollen tube enters the synergid and releases two male gametes. One fuses with the egg cell (Syngamy) to form the diploid Zygote. The other fuses with the two polar nuclei (Triple Fusion) to form the triploid Primary Endosperm Nucleus (PEN). The zygote develops into the Embryo, and the PEN develops into the Endosperm (provides nutrition). Endosperm development precedes embryo development. A common type is free-nuclear endosperm (e.g., coconut water). The embryo consists of an embryonal axis and cotyledons (one in monocots called scutellum).

Post-fertilization events convert the ovule into a Seed and the ovary into a Fruit. Seeds can be Albuminous (retain endosperm, e.g., wheat, maize, castor) or Non-albuminous (endosperm consumed, e.g., pea, groundnut). Residual nucellus is called Perisperm (e.g., black pepper, beet). Fruits can be True (ovary only), False (thalamus contributes, e.g., apple, strawberry), or Parthenocarpic (seedless, without fertilization, e.g., banana). Some plants exhibit Apomixis (seeds without fertilization, mimics sexual reproduction, e.g., Asteraceae, grasses) or Polyembryony (multiple embryos, e.g., Citrus, Mango).