Division : Angiospermae (Angios = enclosed, vessel; sperma = seed)
The Angiospermae is the most advanced division of the flowering plants. The Angiosperms are flowering plants in which seeds are enclosed within the fruit.
The Angiosperms is a group of highly evolved plants, primarily adapted to terrestrial habitat. They vary in size; e.g. Wolffia is the smallest angiosperms, 1 mm in size and Eucalyptus grows to over 100 meters.
The plant body is differentiated into root, stem and leaves. it has flowers, fruits and seeds. Vascular tissues are well developed. Xylem shows vessels or tracheae while phloem has sieve tubes and companion cells.
Angiosperms show heteromorphic alternation of generations in which the sporophyte is diploid, dominant, autotrophic and independent while the gametophytes (male or female) are recessive, haploid and dependent on the sporophyte. (exist within sporophyte).
Angiosperms are heterosporous. Microscopes (commonly called pollens) are formed in microsporangia. They develop in highly specialized microsporophylls or stamens while megaspores are formed in megasporangia (or ovules) borne on highly specialized megasporophylls called carpels.
Besides the essential whorls of microsporophylls (Androecium) and megasporophylls (Gynoecium), there are accessory whorls of sepals (calyx) and petals (corolla) arranged together to form flowers.
In Angiosperms the pollination is indirect (pollen grains received on stigma) and may be self or cross.
These plants show double fertilization. One male gamete fuses with egg cell and another fuses with secondary nucleus, to form embryo and endosperm respectively. It occurs within the ovule and ovule changes to seed. The ovary simultaneously ripens into a fruit.
Angiosperms are sub-divided into two classes :-
1. Class Dicotyledonae :
These plants have two cotyledons in their embryo. They have a tap root system and the stem is generally profusely branched. The leaves show reticulate venation while the flowers show tetra of pentamerous symmetry.
The vascular bundles of stem are conjoint, collateral and open. In dicots secondary growth is commonly found.
e.g. : Helianthus annuus (sunflower), Hibiscus rosa-sinensis (China rose).
2. Class Monocotyledonae :
These plants have single cotyledon in their embryo. They have adventitious root system and the stem is rarely branched. The leaves generally have sheathing leaf base and parallel venation while the flowers are generally trimerous.
The vascular bundles of stem are conjoint collateral and closed. In monocots, secondary growth is absent due to absense of cambium.
e.g. Zea mays (Maize), sorghum vulgare (Jowar).