THALLOPHYTA, BRYOPHYTA AND PTERIDOPHYTA
The first level of classification among plants depends on whether the plant body has well-differentiated, distinct parts. The next level of classification is based on whether the differentiated plant body has special tissues for the transport of water and other substances. Further classification looks at the ability to bear seeds and whether the seeds are enclosed within fruits.
Thallophyta
Plants that do not have a well-differentiated body design fall in this group. The plants in this group are commonly called algae. These plants are predominantly aquatic. Examples are Spirogyra, Ulothrix, Cladophora, Ulva, and Chara (see Fig. 7.5).
Figure 7.5: Thallophyta – Algae
Bryophyta
These are called the amphibians of the plant kingdom. The plant body is commonly differentiated to form the stem and leaf-like structures. However, there is no specialised tissue for the conduction of water and other substances from one part of the plant body to another. Examples are moss (Funaria) and Marchantia (see Fig. 7.6).
Figure 7.6: Some common bryophytes
Pteridophyta
In this group, the plant body is differentiated into roots, stems, and leaves and has specialised tissue for the conduction of water and other substances from one part of the plant body to another. Some examples are Marsilea, ferns, and horsetails (see Fig. 7.7). The reproductive organs of plants in all these three groups are very inconspicuous, and they are therefore called ‘cryptogams’, or ‘those with hidden reproductive organs’.
On the other hand, plants with well-differentiated reproductive parts that ultimately make seeds are called phanerogams. Seeds are the result of the sexual reproduction process. They consist of the embryo along with stored food, which assists for the initial growth of the embryo during germination. This group is further classified, based on whether the seeds are naked or enclosed in fruits, giving us two groups: gymnosperms and angiosperms.
Figure 7.7: Pteridophyta
Source: This topic is taken from NCERT TEXTBOOK
GYMNOSPERMS AND ANGIOSPERMS
Gymnosperms
This term is derived from two Greek words: gymno– means naked and sperma– means seed. The plants of this group bear naked seeds and are usually perennial, evergreen and woody. Examples are pines and deodar (see Fig. 7.8 for examples).
Figure 7.8: Gymnosperms
Angiosperms
This word is made from two Greek words: angio means covered and sperma– means seed. These are also called flowering plants. The seeds develop inside an ovary which is modified to become a fruit. Plant embryos in seeds have structures called cotyledons. Cotyledons are called ‘seed leaves’ because in many instances they emerge and become green when the seed germinates. The angiosperms are divided into two groups on the basis of the number of cotyledons present in the seed. Plants with seeds having a single cotyledon are called monocotyledonous or monocots. Plants with seeds having two cotyledons are called dicots (see Figs. 7.9 and 7.10).
Figure 7.9: Monocot
Figure 7.10: Dicot
Activity 7.2:
* Soak seeds of green gram, wheat, maize, peas, and tamarind. Once they become tender, try to split the seed. Do all the seeds break into two nearly equal halves?
* The seeds that do are the dicot seeds and the seeds that don’t are the monocot seeds.
* Now take a look at the roots, leaves, and flowers of these plants.
* Are the roots tap-roots or fibrous?
* Do the leaves have parallel or reticulate venation?
* How many petals are found in the flower of these plants?
* Can you write down further characteristics of monocots and dicots on the basis of these observations?
Questions
1. Which division among plants has the simplest organisms?
2. How are pteridophytes different from the phanerogams?
3. How do gymnosperms and angiosperms differ from each other?
Source: This topic is taken from NCERT TEXTBOOK