What are cryptograms?

Hint: In the Plant kingdom, all the taxonomic groups below gymnosperms are devoid of advanced characters such as the production of seed. Cryptogams can be divided into algae, lichens, mosses, ferns, fungi, slime molds, and bacteria.

Complete answer:
A cryptogam is a plant that reproduces with the help of spores. The word "Cryptogamae" implies ‘hidden reproduction', referring to the fact that they do not produce any reproductive structure, seed, or flower and therefore, called ‘lower plants', ‘spore plants'.
Cryptogams are classified into 3 groups based on the various structural and functional criteria of the plant:
Thallophyta: Thallophyta is a division of the plant kingdom including primitive forms of plant life showing a simple plant body. They lack roots, stems, or leaves. They possess single called reproductive structures and lack xylem and phloem. It includes algae-like Cladophora, Ulothrix, Spirogyra, Chara, Laminaria, Sargassum, etc.
Bryophyta: Bryophytes comprise a limited variety of non-vascular land plants. They prefer moist habitats but they can survive in dry environments too. Example- hornworts, liverworts, mosses, etc.
Pteridophyta: A pteridophyte is a vascular plant that disperses spores. It is the first plant to have xylem and phloem. The sporophyte of pteridophytes is well-differentiated into stem, root, and leaves. Example- Pteris, Selaginella, Adiantum, Equisetum, etc.

Note:
-Since bryophytes can survive in both water and land, they are considered as the 'amphibians of the plant kingdom'.
-The most unique characteristic of thallophyta is that it can produce glucose after photosynthesis and a part of it is consumed immediately, and the rest is stored as starch.
-The naming and identification of cryptogams are solely done by the International Code of Nomenclature for algae, fungi, and plants.