Classification of Bryophytes (Riccia) PDF

# CLASSIFICATION OF BRYOPHYTES ## OUTLINE OF CLASSIFICATION BY ROTHMALER AND OTHERS ### Division: Bryophyta #### Class 1: Hepaticopsida - The members of the class are commonly termed liverworts. - Plants are not differentiated into root, stem and leaves, or foliose (differentiated into stem and leav...

# CLASSIFICATION OF BRYOPHYTES ## OUTLINE OF CLASSIFICATION BY ROTHMALER AND OTHERS ### Division: Bryophyta #### Class 1: Hepaticopsida - The members of the class are commonly termed liverworts. - Plants are not differentiated into root, stem and leaves, or foliose (differentiated into stem and leaves). - Sex organs either develop at the lips of erect branches or on the dorsal surface of the thallus. - The sporophyte is differentiated into foot and capsule. - In some species seta is also present. - The sporogenous cells develop from endothecium. - The capsule wall is several layered. - Includes three orders: - Sphaerocarpales - Marchantiales (Marchantia, Riccia, Pellia, Porella) - Jungermanniales - The class includes 9 families, 225 genera, and 8,500 species. #### Class 2: Anthocerotopsida - The class includes bryophytes commonly called hornworts. - The gametophyte is thalloid mostly and dorsiventrally differentiated. - Sex organs are embedded on the dorsal surface of the thallus. - The sporogonium is elongated and consists of foot, a meristematic region, and capsule. - The sporogenous cells develop from amphithecium. - The capsule wall is many layered. The outer layers contain stomata and chloroplasts. - There is a central sterile column of tissue in the center of the capsule called columella. - The class includes one order, Anthocerotales, 3 families, 6 genera, and 301 species. #### Class 3: Bryopsida - The members of the class are commonly called mosses. - The gametophyte consists of prostrate filament from which erect branches arise. - The erect branches bear spirally arranged leaves. - The sex organs develop at the tips of special erect branches, the gametophores. - The sporophyte is differentiated into foot, seta, and capsule. - The capsule is well-developed. The outermost capsule wall layer contains stomata. - The sporogenous cells develop from the outer layer of endothecium. - A central sterile column, the columella, is present in the center of the capsule. - The class includes 3 sub-classes: - Sphagnidae (Sphagnum) - Andreaeidae (Andreaea) - Bryidae (Funaria, Polytrichum) - The class includes 28 families and 14,504 species. ## RICCIA ### Systematic Position - Division: Bryophyta - Class: Hepaticopsida - Order: Marchantiales - Family: Ricciaceae - Genus: Riccia - Riccia belongs to the family Ricciaceae of the order Marchantiales. - Majority of the species of this genus are terrestrial but some species are aquatic. - Riccia species have been commonly reported from the North Western Himalayas and the Punjab plains. - The most common species are: - *Riccia robusta* - *R. melanospora* - *R. cruciata* - *R. sanguinea* - *R. himalayansis* - *R. fluitans* - *R. pathankotensis* - *Riccia robusta*, *R. sanguinea*, and *R. pathankotensis* are very common in the Punjab plains (found growing on the moist soil in places like river beds, banks of rivers and canals, and along the streams.) ### Vegetative Structure - Riccia is a thallose liverwort in which the vegetative plant, which is a gametophyte, generally forms rosettes due to the crowded growth of the thallus lobes. - The crowded growth of the various lobes is due to the repeated dichotomies of the thallus. - The thallus lobes are flat growing horizontally on the soil and each lobe has a small notch at the apex where the growing point is situated. - The lobes are thicker in the middle and gradually become thinner towards the margins. - A deep cleft or furrow is commonly present in the middle of each lobe on the dorsal side. The sex organs are found embedded in this furrow. - The lobes in *Riccia fluitans*, which is an aquatic species, are narrow and ribbon-like having repeated dichotomous branches which do not form any rosettes. - Numerous unicellular rhizoids are found attached to the ventral side of the thallus, these rhizoids are generally crowded in the middle part of the thallus and are of two types: smooth and tuberculate as in Marchantia. - The ventral side also bears scales which are formed of a single layer of cells and are arranged in two rows in the older parts of the thallus while in the younger parts these scales are in one row and in the apical region are crowded below the notch for the protection of the growing point. ### Internal Structure of the Thallus - The thallus of Riccia has a simple structure and is formed of parenchymatous cells which are bounded on both sides by the upper and lower epidermis. - Internally the thallus is differentiated into two regions: upper assimilatory region and the lower storage region. - The storage region is formed of compactly arranged parenchymatous cells which are either colourless or contain only few chloroplasts, but these cells are rich in starch grains. Some of the cells of the lower epidermis grow out and elongate forming the rhizoids, while certain cells divide and produce the single layered scales. - In the majority of species the assimilatory region is formed of vertical rows of cells which are about six to eight cells in height and are separated by large air spaces. - The cells of these filaments are rich in chloroplasts as these form the main photosynthetic tissue. - The cells of the upper epidermis are also loosely placed having spaces in between them which function as pores through which the underlying air spaces communicate out for the exchange of gases. - In some species the assimilatory region is spongy being formed of irregularly placed air spaces which are separated from each other by single layered partitions whose cells are rich in chloroplasts. ### Reproduction - Riccia plants, like other liverworts, multiply vegetatively by the decay or death of the older parts which results in the separation of younger branches, each of which grows into an independent plant. - In certain species (*R. fluitans*) small adventitious lateral branches may be produced from the ventral side of the thallus, these adventitious branches on detachment give rise to new plants. - Formation of vegetative reproductive gemma-like multicellular bodies at the apices of rhizoids have also been reported in certain species.