Angiosperms are the flowering plants, the most advanced and diverse group of plants. This chapter covers their characteristics, the parts of a flowering plant (root, shoot, leaf and flower), the terms used to describe flowers, and four important plant families.
Characteristics of angiosperms
- They are diploid sporophytes.
- They can grow as trees, shrubs, bushes and herbs.
- The herbaceous plants may be ephemerals, annuals, biennials or perennials.
- They show great variation in their habitat, habit and mode of life.
- Usually they are autotrophs, and a few are heterotrophs.
Types of angiosperms
Monocotyledons (monocots): Angiospermic plants that have only one cotyledon in their embryo, with adventitious roots, simple leaves with parallel venation and trimerous flowers. Examples: banana, cereals, bamboos.
Dicotyledons (dicots): Angiospermic plants that have two cotyledons in their embryo, with a taproot system and reticulate venation in their leaves. Examples: sunflower, tomato, pea, mango.
Habit of plants
- Herbs: small branched or unbranched plants with soft stems.
- Shrubs: medium-sized plants that produce branches from their base to form a bushy shape.
- Trees: tall, strong, perennial plants.
Life span of plants
- Annual: completes its life cycle from seed germination to seed production, followed by death, within a single season or year. Example: maize.
- Biennial: lives for two years to complete its life cycle, growing vegetative parts during the first year and fruiting or dying during the second year. Example: carrot.
Habitat of plants
- Mesophytes: grow in soils with sufficient moisture and air. Example: mustard.
- Xerophytes: grow in dry and sandy soils. Example: Opuntia.
- Hydrophytes: grow in water and in damp, marshy places. Example: Hydrilla.
- Epiphytes: grow on trees for support but do not live parasitically. Example: Vanda.
- Parasites: live on or in another plant and absorb food from it. Example: Cuscuta reflexa.
- Saprophytes: obtain organic matter from dead and decaying parts of plants or animals. Example: Monotropa uniflora.
- Insectivorous plants: nearly autotrophic plants that capture insects with specially modified leaves and digest the soft parts of the prey. Example: pitcher plant.
The root system
The root is the non-green, descending part of a vascular plant that grows downward into the soil. It is negatively phototropic but positively geotropic.
- Taproot: arises from the radicle of the embryo and develops into a primary root that grows vertically downward. It bears secondary and tertiary roots.
- Fibrous (adventitious) root: develops from any part of the plant body except the radicle.
The shoot system
The stem together with its branches, leaves, flowers and other appendages is called the shoot system.
- Erect stem: the common aerial stem that is strong enough to remain upright without external support.
- Weak stem: thin, soft and weak stems that cannot stand erect and need support to grow.
The leaf (phyllopodium)
The leaf is a thin, flattened, green outgrowth of the stem or its branch, borne at a node and having a bud in its axil. It has limited growth. A typical leaf has three main parts:
- Leaf base
- Petiole
- Lamina
The lamina bears the apex, margin, veins and midrib. An axillary bud lies in the axil, and stipules may be present at the base.
Phyllotaxy: the arrangement of leaves on the stem and branches.
Stipules:
- Stipulate: leaves having stipules at the base.
- Exstipulate: leaves without stipules.
Petiole:
- Petiolate: leaves that have a petiole.
- Sessile: a leaf that does not have a petiole.