Riccia Morphology and Reproduction

Riccia Morphology and Reproduction

• Riccia is a bryophyte, with a dominant and independent haploid gametophyte phase.
• The gametophyte forms a dorsiventrally flat thallus, shaped as circular patches or rosettes on moist substrates.
• The thallus is dichotomously branched, with a dorsal groove or midrib.
• A growing point is located at the tip, and the thallus attaches to the substrate via rhizoids.
• Rhizoids are unicellular, smooth-walled, or tuberculate, aiding in anchorage and absorption.
• Multicellular, violet, obliquely placed scales retain moisture on the thallus.

Thallus Structure and Function

• The thallus displays a distinct upper photosynthetic region and a lower storage region.
• Photosynthetic filaments composed of chlorenchyma cells are arranged in parallel rows within the photosynthetic region, with air canals in between.
• Terminal cells of these filaments are globular and hyaline/transparent, forming a discontinuous upper epidermis.
• The lower storage region consists of parenchymatous cells that store food material.
• Sex organs (gametangia) are embedded within the storage region.

Sexual Reproduction

• Riccia is homothallic, meaning both male and female gametangia develop within the same thallus.
• Gametangia are embedded in the storage region.
• Male gametangia (antheridia): Located just below the dorsal groove, each antheridium comprises a stalk and a globular body. The body is encased by a sterile jacket that contains motile antherozoids or male gametes.
• Female gametangia (archegonia): Also located just below the dorsal groove, each archegonium is flask-shaped, with a venter enclosing an egg. A neck region with neck canal cells surrounds the venter.

Sporophyte Development

• After fertilization of the egg by an antherozoid, a diploid zygote forms, initiating the sporophytic generation.
• The sporophyte is exceptionally simple, consisting only of a capsule.
• The capsule is enclosed by a protective calyptra, developed from the venter of the archegonium.
• A sterile jacket encloses diploid sporocytes, which undergo meiosis, generating haploid spores.
• The calyptra disintegrates, releasing the spores.
• Each spore is triangular, unicellular, and uninucleate, with an outer spiny exosporium and an inner smooth endosporium.
• Mature spores germinate to produce a new haploid gametophyte.
• Foot and seta are absent in the sporophyte of Riccia.

Explore the fascinating morphology and reproduction of Riccia, a type of bryophyte. This quiz will cover the unique features of Riccia's gametophyte phase, thallus structure, and the roles of rhizoids and scales. Test your knowledge on how these characteristics enable Riccia to thrive in moist environments.