The Basics of Flowering

The process of flowering in plants is complex and involves several stages, which can be broadly classified into developmental and physiological phases. Here's an overview of how plants flower:

Flowering Process Overview

Initiation

• Plants often rely on environmental cues such as light duration (photoperiod), temperature, and water availability to trigger flowering. These signals help plants determine the appropriate time to flower for optimal reproduction.

• Flowering is controlled by a series of genes and regulatory networks. In response to environmental signals, plants activate these genes to initiate the flowering process.

Development

• The flowering process begins with the development of an inflorescence, which is a cluster of flowers arranged on a single stem. The structure of the inflorescence varies widely among plant species.

• Within the inflorescence, individual flower buds begin to form. Each bud develops the necessary structures to become a complete flower.

Flower structure formation

• These are the outermost parts of the flower, which protect the developing bud.

• Petals are often brightly coloured and serve to attract pollinators.

• These are the male reproductive parts of the flower, consisting of anthers (which produce pollen) and filaments.

• The female reproductive parts, including the stigma (where pollen lands), style (a tube connecting the stigma to the ovary), and ovary (which contains ovules).

Pollination

• Pollination occurs when pollen from the anthers of a flower is transferred to the stigma of the same flower or another flower of the same species. This can be facilitated by wind, water, insects, birds, or other animals.

• Once pollen lands on a compatible stigma, it germinates and forms a pollen tube that grows down the style to the ovary, allowing sperm cells to reach the ovules. Fertilisation occurs when a sperm cell fuses with an ovule.

Fruit and Seed Development

• After fertilisation, the ovary develops into a fruit, which houses the seeds. The fruit protects the seeds and aids in their dispersal.

• Seeds develop from fertilised ovules. Each seed contains an embryo, which can grow into a new plant, along with stored nutrients to support initial growth.

Key Factors Influencing Flowering

Photoperiod

Plants can be classified based on their response to day length. Short-day plants flower when the day length is shorter than a critical period, long-day plants flower when the day length is longer, and day-neutral plants flower regardless of day length.

Temperature

Some plants require a period of cold (vernalisation) to flower, while others may require warm temperatures or specific seasonal changes.

Hormones

Plant hormones like auxins, gibberellins, and cytokinins play crucial roles in flower development. For example, gibberellins can promote flowering in some plants.

Genetic factors

Flowering time and flower structure are also influenced by the plant's genetic makeup. Flowering can be regulated by a network of genes and gene interactions.

Environmental Conditions

Factors such as water availability, soil nutrients, and light intensity can affect the timing and success of flowering.

Types of flowering plants

1. Annuals: Complete their life cycle in one growing season and flower once.

2. Biennials: Require two growing seasons to complete their life cycle, with flowering occurring in the second season.

3. Perennials: Flower over multiple years, often producing flowers in each growing season after reaching maturity.

Floral formulas

A floral formula is a way to represent the structure of a flower using specific letters, numbers, and symbols. Typically, a general formula will be used to represent the flower structure of a plant family rather than a particular species. The following representations are used:

Ca = calyx (sepal whorl; e. g. Ca5 = 5 sepals)

Co = corolla (petal whorl; e. g., Co3(x) = petals some multiple of three )

Z = add if Zygomorphic (e. g., CoZ6 = Zygomorphic with 6 petals)

A = androecium (whorl of stamens; e. g., A∞ = many stamens)

G = gynoecium (carpel or carpels; e. g., G1 = monocarpous)

x: to represent a 'variable number'

∞: to represent 'many'

A floral formula would appear something like this:

Ca5Co5A10 - ∞G1

The four main parts of a flower are generally defined by their positions on the receptacle and not by their function. Many flowers lack some parts or parts may be modified into other functions and/or look like what is typically another part. In some families like Ranunculaceae, the petals are greatly reduced and in many species the sepals are colorful and petal-like. Other flowers have modified stamens that are petal-like, the double flowers of Peonies and Roses are mostly petaloid stamens. Flowers show great variation and plant scientists describe this variation in a systematic way to identify and distinguish species.

Specific terminology is used to descried flowers and their parts. Many flower parts are fused together; fused parts originating from the same whorl are connate, while fused parts originating from different whorls are adnate, parts that are not fused are free. When petals are fused into a tube or ring that falls away as a single unit, they are sympetalous (also called gamopetalous). Petals that are connate may have distinctive regions: the cylindrical base is the tube, the expanding region is the throat and the flaring outer region is the limb. A sympetalous flower, with bilateral symmetry with an upper and lower lip, is bilabiate. Flowers with connate petals or sepals may have various shaped corolla or calyx including: campanulate, funnel form, tubular, urceolate, salverform or rotate.