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The following points highlight the top eighteen characteristic features of Angiosperms.
1. The sporophyte which is the dominant plant in the life-cycle is differentiated into roots, stem and leaves.
2. The highest degree of perfection of the vascular system with true vessels in the xylem and companion cells in the phloem.
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3. The organisation of the microsporophyll’s (stamens) and megasporophylls (carpels) into a structure called the flower, which is typical only of the angiosperms.
4. The presence of four microsporangia (pollen sacs) per microsporophyll (stamen).
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5. The ovules are always enclosed in an ovary which is the basal region of the megasporophyll.
6. Production of two kinds of spores, microspores (pollen grains) and megaspores. Angiosperms thus are heterosporous.
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7. Presence of single functional megaspore which is permanently retained within the nucellus or mega-sporangium.
8. Adaptation of flower to insect pollination.
9. Pollination consists in the transference of pollen grains from anther to stigma.
10. Spore dimorphisim having resulted in the production of gametophytes, male and female.
11. Extreme reduction in size, duration of existence and complexity of the structure of the gametophytes which are entirely parasitic.
12. The male gametophyte has reached the limits of reduction. It consists only of the pollen grain and the pollen tube contains the tube nucleus and two male gametes or nuclei. The male cells (gametes) are non-ciliated.
13. The female gametophyte lacks any extensive development of vegetative tissue. It consists of three egg apparatus cells, three antipodal cells and two polar nuclei in the centre of the embryo sac.
14. The non-motile male cells or nuclei are carried bodily to the neighborhood of egg apparatus by the pollen tube.
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15. The seed or seeds remain enclosed in the ripened ovary called the fruit.
16. The phenomenon of double fertilization or triple fusion is the characteristic of the angiosperms.
17. The endosperm develops after fertilization. It is triploid.
18. The angiosperms are completely adapted to life on land.
